How Many Planets Are In The Universe?

"Stuff your eyes with wonder, live as if you'd drop dead in ten seconds. See the world. It's more fantastic than any dream made or paid for in factories." -Ray Bradbury

It wasn't all that long ago -- back when I was a boy -- that the only planets we knew of were the ones in our own Solar System. The rocky planets, our four gas giants, and the moons, asteroids, comets, and kuiper belt objects (which was only Pluto and Charon at the time) were all that we knew of.

Image credit: NASA's Solar System Exploration,

But these were just the worlds around our Sun, which houses (according to current definition) eight planets. Our Sun is just one of an estimated two-to-four hundred billion stars in our Milky Way galaxy, and looking up towards the night sky, one can't help but wonder how many of those stars have planets of their own, and what those worlds are like.

Image credit: Free Roaming Photography, by Mike Cavaroc.

There are a vast variety of stars out there in our galaxy. Our Sun is just one example -- a G-class star -- of seven different main types.

Image credit: Wikipedia user Kieff; annotations by me.

We may think of our Sun as being typical and on the relatively dim side, since a disproportionate number of stars visible to our eyes in the night sky are O, B, and A-class stars. But in reality, the Sun is more massive and intrinsically brighter than 95% of stars in our galaxy. The red dwarf stars -- M-class stars -- which are no more than 40% the mass of our Sun, make up 3 out of every 4 stars that are out there.

What's more than that, our Sun exists in isolation; it is not gravitationally bound to any other stars. But that is not necessarily how stars exist in the galaxy, either.

Image credit: VISTA infrared survey, ESO / J. Borissova.

Stars can be clustered together in twos (binary stars), threes (trinaries), or groups/clusters containing anywhere from hundreds to many hundreds of thousands of stars.

My point is this: if you want to accurately estimate how many planets there are in our galaxy, you can't just take the number of planets we find around our star and multiply it by the number of stars in our galaxy. That's a naïve estimate that we'd make in the absence of evidence. But just for fun, that'd give us somewhere around two-to-three trillion planets in our galaxy. And as we know from our own Solar System, there's a great variety of what the surfaces of those planets could look like.

Image composite: credit Mike Malaska. For individual image credits, see lower left.

But over the past two decades, we've been looking. We've been looking with a few different methods, in fact, and the two most prolific are the "stellar wobble" method, where you can infer the mass-and-radius of a planet (or set of planets) around a star by observing how it "wobbles" gravitationally over long periods of time:

Image credit: European Southern Observatory.

And the transit method, where the light coming from a distant star is partially blocked by the disk of a planet in its solar system passing in front of it.

Image credit: ESA / NASA's Solar And Heliospheric Observatory (SOHO), 2006.

It's important to recognize, when we do this, that we will not see the vast majority of planets that are out there. Take NASA's Kepler Mission, for instance, which has discovered hundreds (if not thousands) of planets by looking at a field-of-view containing around 100,000 stars. But that does not mean that there are only a few planets-per-hundred-stars. Consider the following: if Kepler were looking at our Solar System, and our Solar System was oriented randomly with respect to our perspective, these are the odds that the alignment would be good enough to observe a transit of our star by one of our planets.

Planet Degree Range (out of 180) % chance of good alignment
Mercury 1.37 degrees 0.76% chance
Venus 0.738 degrees 0.41% chance
Earth 0.533 degrees 0.30% chance
Mars 0.320 degrees 0.18% chance
Jupiter 0.101 degrees 0.056% chance
Saturn 0.0556 degrees 0.031% chance
Uranus 0.0277 degrees 0.015% chance
Neptune 0.0177 degrees 0.0098% chance

Now you may think those are not-so-good odds, but you don't even know the half of it. Mercury and Mars are too small, meaning they don't block enough of the Sun's light, to be detectable with Kepler, and the four outer planets, despite their large sizes, take too long to orbit for Kepler to observe more than one transit, a necessity for a planetary candidate.

So this means that if Kepler were looking at 100,000 stars identical to our own, it would have found 410 stars with a total of 700 planets around them.

Illustration credit: NASA / Jason Rowe, Kepler Mission.

But as of today, Kepler has found over 11,000 stars with at least one planetary candidate, and over 18,000 potential planets around those stars, with periods ranging from 12 hours up to 525 days. In other words, there are:

  1. a huge variety of planetary systems out there, most of which are very different from our own,
  2. orbiting a wide variety of stars, including binary and trinary systems,
  3. and we are only seeing the ones that are large enough, orbiting their stars close enough, that also have unlikely, fortuitous alignments with respect to our line-of-sight.

You may have read this week that there are at least 100-to-200 billion planets in our Milky Way, and that's true, but that's not an estimate; that's a lower limit. If you instead were to make an estimate, you'd get a number that's at least one (and more like two, if you're willing to make inferences about outer planets) orders of magnitude higher: closer to ten trillion planets in our galaxy, alone!

Image credit: ESO / M. Kornmesser.

In other words, based on what we've seen so far, most stars are likely to have planets, and based on what we've seen in the inner solar systems of the ones that do, a large fraction of them are likely to have more rocky planets in their inner solar systems than even our own has, to say nothing of the outer solar system!

Image credit: J. Pinfield / RoPACS network / University of Hertfordshire.

This doesn't even include orphan planets (without a parent star), which we know exist, even if we don't know their numbers yet. Over time, we'll continue to learn more and refine our estimates, but right now, there are at least about as many planets as there are stars in our galaxy, and quite possibly many, many more than even eight times that number.

Our solar system may turn out to be average, slightly above average, or somewhat below average; we're still not sure. But regardless of which way it goes, we're talking about trillions of planets in our galaxy alone. And remember, our galaxy isn't alone in the Universe.

Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team.

With at least 200 billion galaxies out there (and possibly even more), we're very likely talking about a Universe filled with around 1024 planets, or, for those of you who like it written out, around 1,000,000,000,000,000,000,000,000 planets in our observable Universe.

That number's only going to get more accurate, but I'm tired of people giving the lowball-estimate when it's eminently likely that there are so many more. Let's keep looking, for not just planets, but for water, oxygen, and signs of life. With all of those chances, we're bound to get lucky if we persevere and look hard enough!

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ouch! hurts my head but it's so good! Thanks Ethan again

Fermi's Paradox doesn't seem like much of a paradox to me.

However, I sometimes wonder if the irony might be that we live in a universe (potentially filled with life) that can't ever be visited by any member of that universe just due to the laws of physics of that universe.

If travel at some fraction of the speed of light is an absolute limit and if the closest star/planet is too far away for us to ever reach it then whether the universe has abundant life or not is almost a moot point if we can never observe it.

Thanks for the post!
More people should read it to understand we are a very small part of the universe.

What a exciting time are we living!!

Looking at it statistically there has to be life on more than just the Earth. Think about it, the elements we're made from are common throughout the galaxy! We are after all star dust.

And it can't be just our little G2V star that has life circling around it.

Very nice summary.
I did not know a lot of the things you explained and put in perspective.

Fascinating "mind opener". Thank you dear Ethan.

By Skywalker (not verified) on 06 Jan 2013 #permalink

Wonderful post. Thank you.

By theTentman (not verified) on 06 Jan 2013 #permalink

For a while, I have been wanting to get some sort of visualization tool for the #'s of "things" in the universe. I was thinking of the # of grains of sand on a beach compared to the # stars, galaxies, etc. Your post today was a prod to do it.
Assume - beach 30 meters wide, 1 meter deep. Sand - 8 grains/cubic MM (

So, with a little rithmetic, we can get the length of a beach corresponding to these things:
1) number of galaxies - 0.83 meters. - OK, I can visualize that, and it is a lot
2) Number of stars in our galaxy - 1.66 meters.
3) number of stars in the observable universe - the beach would be 333,333,333 Km long. (207,100,000 miles for those of us mired in the English system) Now things are getting out of hand
4)(gulp) # of planets in the universe. - the beach would be 4,166,666,667 Km (2,588,750,000) miles long. This is pretty close to the distance to neptune.
Well, that was interesting, at least to me.

By Phil Shaffer (not verified) on 06 Jan 2013 #permalink

Until recently I had imagined that the stellar wobble method for finding exoplanets would involve measuring the visible change in a star's position as viewed from the earth, for example right-to-left and back again. I learned just last week in the book store that this isn't the case, though, and that you can get much more accurate measurements from the redshift and blueshift of the star's light as it moves in the plane towards us and away from us.

This made me think that just as the transit method requires a system be edge-on to us, the Doppler method would require that a system not be oriented so that we view it directly, or almost directly, from above or below--since this would mean the star didn't move, or hardly moved, in a Doppler-detectable direction.

So: how big would this blind zone of star system orientations be, what percentage of systems would we expect to fall into it, and is it a factor in counting/estimating the number of planets?

I don't think anything has ever fired up my imagination the way the search for exoplanets does! I would quite happily die tomorrow if I could spend the time until then poring over a photo album of gorgeous, strange scenes from other planets in our galaxy.

By uncleMonty (not verified) on 06 Jan 2013 #permalink

There's a transverse effect to the dopler shift.

Smaller. But there.

Huh, so I wonder how you tell the difference between a small Doppler effect that's due to a large planet in a "bird's eye" system, versus the same small effect that's due to a (relatively) small planet in an edge-on system... can we tell which plane a sun-sized star is spinning in?

By uncleMonty (not verified) on 06 Jan 2013 #permalink

So , using doppler shift, if we are looking directly in the plane of the solar system, we will see a particular red shift. If we are at 90 degrees, we should see no redshift (I see above the transverse red shift, but I don' understand this, so I am ignoring it - Call it poetic license.
Now in the intermediate case, say 45 degrees, the redshift will be present, but half of what you would expect in the edge on case.
Now - here is my question - since the degree of redshift depends on the angle at which we view it, how is it possible to correct for this when trying to calculate the mass of the planet?
Also, in the pure situation of one large planet, the redshift method is clear, but let's say there are 4 large planets. The redshift will be a very complex curve. How does one compute the number and mass of each planet.

(i'm waiting for the answers here to start work on the data I gathered last night ;)

By Phil Shaffer (not verified) on 06 Jan 2013 #permalink

Phil as I understand it when there are more planets you have to decompose the complex curve into its constituent parts, much as you decompose a soundwave into its constituent (pure sinusoidal) partials, by e.g. Fourier transform.

You had the same question as me above about decoupling the mass effect from the angle effect, but it's not a problem if we can detect how the star is rotating--then we know how much to correct by. And it seems, after a little more searching online, that there are methods for finding a star's rotational velocity and direction. At least, I've seen it's possible for some stars though I haven't yet seen explicit confirmation that it's possible for sun-like stars.

By uncleMonty (not verified) on 06 Jan 2013 #permalink

Oh and it's not hard to imagine the small Doppler shift in a system seen from above: a pure sideways motion, as seen from earth, will mean the star is very slightly further away at the endpoints of its lateral motion. Imagine a very long equilateral triangle with the earth at the skinny part and the other two corners the extreme points of the star's apparent excursion. When the star is at the center of its motion, forming a right-angled triangle with the earth and either extreme, a little trigonometry will give the difference in length between the two long sides.

By uncleMonty (not verified) on 06 Jan 2013 #permalink

sorry, I meant isoceles triangle, not equilateral, of course.

By uncleMonty (not verified) on 06 Jan 2013 #permalink

Even if only 0.000001% of 150 billion have life on them, that's still 15000 planets with life in our milky way! And if only 1% of those have intelligent life, that's 1500 planets with different races.. amazing :) Starfleet here we come ;)

By Sinisa Lazarek (not verified) on 06 Jan 2013 #permalink

sorry... last number should be 150 not 1500

By Sinisa Lazarek (not verified) on 06 Jan 2013 #permalink

even at 1500 planets, that makes an average distance between them of around 6000 light years between each system.

To be honest, that's why sci fi ALWAYS has FTL travel. The reality, without FTL travel, is that you leave one planet to colonise another and never heard from again.

Even if you were a creature living 10 million years, you wouldn't bother with a conversation that took 12,000 years for each message/response.

I've concluded, as GB seems to say, that in spite of all the intelligent life there likely is, we'll never meet. The distances are too great. Contrary to GB saying "filled with life", the galaxy is an immensely huge void with tiny specks of life scattered very far apart.

Dr Rod, the galaxy might be mind-bogglingly huge, but it's also mind-bogglingly old - so old that there could be (and I'd bet there are) civilizations* out there that watched their home star burn out before ours even formed. They've had more than enough time to fully explore the galaxy.

They'll also be technologically immortal, so it doesn't have to be restricted to von Neumann self-replicating space probes either (which could do the job, travelling no quicker than 0.1c, in just half a million years: )

*unless it's just the one... First civ to get out there basically claims the lot. Civs 2+ will be so far behind (odds of similar tech levels meeting are tiny), that the oldest will be galaxy-spanning before the second one gets off its planet.

By Mark McAndrew (not verified) on 06 Jan 2013 #permalink

@uncleMonty: The "radial velocity method" (those are the right Google keywords) uses the main Doppler shift, not the transverse. The magnitude of the shift (often translated into velocity) is fit to a Keplerican (orbital) oscillation with the planet's mass and the orbital inclination both unknown.

The result gives you the planet's mass in the form "M sin i", where sin(i) is the sine of the inclination angle: 0 degrees is edge on, and 90 degrees is face on.

The fit is more complicated with a multiple-planet system, but you can do it where the "sin i" is common to all terms. That may not be strictly true (it isn't exact for our Solar System), but it's close enough to get decent fits, as well as to rule out spurious signals (like stellar oscillations).

As Ethan wrote, the transit system is limited to essentially edge-on systems (sin i ~ 1). When you can apply both methods to the same star, you can derive "exact" masses for the planets.

By Michael Kelsey (not verified) on 06 Jan 2013 #permalink

Ethan, based on these numbers, what would be the latest value (estimate) of the Drake equation?

In response to Phil S. about visualization...

I once had a book called "One Million". It consisted of one million dots printed several thousand to a page. Every once in a while, a dot was singled out with an annotation: "Number of Hindus in Brazil", "Telephones in China", "Days since the founding of Rome", and at the end of the book "Number of dots in this book".

Using grains of sand (or anything on the mm^3 scale) to visualize "billions" is pretty nice. If you took that stretch of beach that corresponds to the number of stars in the Milky Way galaxy and scattered the sand into a scale model of the galaxy, with the average grain (0.5 mm diameter) corresponding to the Sun's diameter (1.4e9 m), the model of the galaxy (1.1e5 ly, or 1.04e21 m) would extend about 7.4e11 sand grains, or 370,000 km -- roughly the distance from the Earth to the Moon.

By Joe Barsugli (not verified) on 06 Jan 2013 #permalink

One point we all seem to be missing is the huge uncertainty in one element of the drake equation (an equation that lays out the factors that multiplied together determine the probable number of detectable extraterrestrial civilisations out there). The really big unkown is fl - the fraction of potentially habitable planets that go on to develop life. We simply have no idea what this number should be. It could be close to unity, or on the other hand it could sit at the ten to the power minus 100 and above level. We don't know because we are still pretty much in the dark about how the first life evolved on our planet. Until we have a good understanding of that we will simply be guessing wildly at this key number. And it makes a huge difference - put in 10 to the minus 100 and even with Ethan's 10 to the 24 planets the probablitiy of life out there is essentially zero. We must simply admit that based on planet numbers etc at this moment we have no idea if there is likely to be life out there.

By Waterbergs (not verified) on 06 Jan 2013 #permalink

Heck the surface of the earth can be described as that wrt people.

Just imagine if there were no telegraph and no transport beyond legs or swimming.


Don't despair! Actually, the laws of physics does allow to reach many of the surrounding worlds, even to the point, that there's the theoretical possibility to coast around a good bit of the observable universe. It's all in the laws of relativity.

First of all, the only theoretical speed limit we're aware of is that of the speed of light. While there's a lot of reason why we can't reach even fraction of that speed today in respect to the rest of the universe, none of us can really predict what we will be capable of doing within let say 200 years. We certainly have come a long way since 1813 the steam locomotive was only spanking new invention just about the change our idea of mass transport. We already have theoretical design for interstellar spacecraft, and the most likely design that would eventually enable to travel interstellar distances in human life time is going to be something similar to the Bussard ramjet (

In short the idea is to provide constant acceleration by the help of the interstellar medium. While the interstellar medium is scarce, as the spacecraft gains relativistic speed, the collection rate would increase.

With relativistic speed (in respect to the rest of the material universe) one will encounter with time dilation which in turn would resolve the problem of reaching vast distances within reasonable time. When you reach around the 88% of the speed of light, you'll start experience serious time dilation (that's where it reaches around the factor 2). As you get closer and closer to the speed of light of course, the time dilation will cut you off from the human race on earth or even in the solar system because the time dilation gets so high that perhaps no one will be alive by the time you decelerate and come to rest in respect to you destination star system.

By progician (not verified) on 07 Jan 2013 #permalink

@Michael: you wrote "@uncleMonty: The “radial velocity method” (those are the right Google keywords) uses the main Doppler shift, not the transverse."
Thanks, that's what I believed in the usual cases but I wondered how it worked for a system whose star we view from one of its poles. In that case there is a tiny Doppler effect, since as the star appears to wiggle from side to side it must also change its distance from us (I think this is what Wow meant), but my back-of-the-envelope makes the effect much too small to do the job. Is that right?

It's too bad that the same systems that are best suited for Doppler methods are also the ones most likely to involve transits.

By uncleMonty (not verified) on 07 Jan 2013 #permalink

Have you ever come across someone's knowledgeable power spectrum estimate of masses in our galaxy, from blue giant to brown dwarf to super-Jupiter to dwarf planet?

And, thanks again for yet another informative piece,

@ Mark McAndrew:

It does no good for a meet-and-greet with alien lifeforms if they already passed through our neck of the galactic woods hundreds of millions of years ago. The age of the universe cuts both ways -- yes it's more than old enough for a hypothetical alien civilization to have explored all of the galaxy, but that doesn't make it any more likely that they'll be right here during the incredibly brief moment we've been around and able to notice and record the fact.

Cool piece. How about a write up on hot jupiters!


"Don’t despair! Actually, the laws of physics does allow to reach many of the surrounding worlds, even to the point, that there’s the theoretical possibility to coast around a good bit of the observable universe."

while you are correct that laws of physics allow, the rest is just bollocks. Just because something is allowed by current laws doesn't mean it's either practical or doable. There is nothing in the laws that prevents i.e. humans evolving wings and flying. There is nothing in the laws that prevents us from building a spaceship powered by a black hole or bad news for that matter. That still doesn't make it real or feasible. And the paper linked is just someone's daydream... Besides, interstellar space is a much greater vacuum than what we have on earth. To "extract" hydrogen from such a vacuum is a joke, even the author realizes it doesn't work so he put's in some nebula in there.... And he somehow fails to address where does the energy for fusion come from.. what powers the ship before it starts "vacuuming" the interstellar hydrogen? All in all.. bullocks.

By Sinisa Lazarek (not verified) on 07 Jan 2013 #permalink

p.s. while thinking more on the subject of hydrogen powered fusion reactor.
It would be much more logical for it to be powered by astronaut piss than interstellar hydrogen. Much more hydrogen atoms in one cup of piss than any that can be scooped up by a ship from the vacuum of space. Wonder why the author didn't think of that.... rofl.

By Sinisa Lazarek (not verified) on 07 Jan 2013 #permalink

A read mind bender. Funny how we enjoy the universe from our stationary planet named earth.

Plug this into the Drake equation, and all you can get so far is that the answer might still possibly be non-zero. With so many planets out there, the odds pretty good that at least some of them are hospitable at least for extremophile bacteria or things like those. The three really big unknowns, though are still:1) getting life (of any type) started on a planet in the first place; 2) getting something like a Cambrian explosion; and 3) making the leap to self-aware intelligence. The combination of these three contingencies might be so rare as to still assure that we are alone.

By Stefan Stackhouse (not verified) on 08 Jan 2013 #permalink


There are as many planets, galaxies, stars, as the power of a telescope can see. I believe that if our telescopes could see infinitely far, we'd see infinitely more celestial bodies out there. Its absurd to try to estimate the that number when we have no idea how big the universe is. We could be seeing only a small portion of it, or it could infinitely big.


I have a longstanding policy (for about four years) of not plucking a bad science article from obscurity to tear into it and talk about the problems with it.

So it's unlikely I'll be sharing my ideas about Lebed's theory; better to leave it alone and let it languish in obscurity where it belongs.

Thank you! That is actually very helpful! :)

By knightEknight (not verified) on 08 Jan 2013 #permalink

Amazing post! Where do you get all the amazing pictures for your post? You always have the best pictures, and I always end up changing my desktop background when I read this blog.

I haven't read all the comments, but a common opinion I see is that even if there is life out there, the distances are too great, and we will "never" be able to reach them. I'm currently reading a book (The Stardust Revolution, which I highly recommend) and in the first few chapters, one person, I forget exactly who, in the 17th or 18th century was certain, absolutely certain, that we would "never" be able to know the composition and chemical make-up of the stars. They're simply too far away. It was less then a century later that spectrography was invented. So, while I won't tell anyone that faster than light travel is certainly possible, I will absolutely keep an open mind, and not underestimate the scientists of the future! Especially looking at how incredibly fast our technology is advancing, and the new doors to the universe it is opening up.

By luminiferousethan (not verified) on 09 Jan 2013 #permalink

" that we would “never” be able to know the composition and chemical make-up of the stars."

And they were right.

We had to get spectroscopy before that could happen, since it's far too far to walk, and we'd die from heat stroke if we tried.

"I will absolutely keep an open mind"

You seem to be preening yourself on this.

However, Captain Obvious, nobody is closing their mind to it. Hell, I'll quote you one that you probably never really read, just read the words you thought would be there:

"The reality, without FTL travel, is that you leave one planet to colonise another and never heard from again."

So even if you want to insist FTL WILL happen, without it, you leave one planet to colonise another and never hear from again.

gotta be '100-to-200 billion stars not planets in the Milky Way'

Presumably, the stellar wobble technique suffers from higher false negative rates, the more planets there are orbiting a given star. It seems intuitive that the more planets there are, randomly positioned (ie not all pulling in the same direction), the closer the system's centre of mass will be to the centre of the star. Has this been analyzed?

By tom campbell-r… (not verified) on 18 Jan 2013 #permalink

Thank You.

By Susan Dos Santos (not verified) on 02 Feb 2013 #permalink

My journey in spirit brings me to the matter that makes up the Universe and the lessons in written word and physical solutions and equations that join me in the matter bring me to this place and space in journey.
So.....that being stated....without knowing Math or Science as well as the books teach.....I would like to just hear thoughts on the hypothesis that as we continue to evolve in this time and space , we can know the past and see the future. Eventually , we will be not only genetically altered and modified but our advancements with travel will advance to use a method that can travel the past universes in which our present selves occupy....and at this time in space.....our life may be altered so much so, as will our universe and planet....we will need to travel back to acquire the only minerals that we would now use for energy and food....(this future may not have agriculture from what we have done to it and the bodies could be technically and so genetically altered .....our food could consist on the same minerals that furl our energy. So ....if we can indeed see the future.....out there....but we can not yet travel to it......Don't you think the future life(whatever it may be) would maybe even want to warn us of the godless hell we are allowing to take shape??! Symbols, messages, equations, letters, creation and the lessons are is our CHOICE to see and use for selfless , Love , positive energy to create and live.....for positive spirits to rise...... we KNOW THE FUTURE.....and it is almost here.....FAITH has continued to prove itself......without my asking.

By skydiamond (not verified) on 10 Feb 2013 #permalink

“Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus.”

― Thomas Jefferson

wow grabe its so wonderful i kant explane mt happiness when i see those pictures that was really awesome god is really braive because hi did that

Awesome!!! That's all I can say. God is great for all He works...

Would it be acceptable to come along to your church and in the sermon start pointing out all the fallacies in the bible?

Really, what you godbotherers are doing is EXTREMELY rude.

Some random thoughts..

As far as bacterial/simple life goes, I would expect it to be widespread. The logic runs this way:

- Life appears in the geological record on Earth basically instantly - the moment it's possible to detect life in rocks, we see it. If life appeared as an extreme-low-probability event there would be no reason to expect this.
- The idea of life emerging as a result of random chemical interactions is essentially impossible. Additionally, there is no conceivable stable state which is a 'half-way house' between simple inorganics and life. You cannot, for example, postulate complex-but-not-self-replicating RNA hanging around for millions of years. Not in liquid water.
- Hence I would postulate that life emerges quickly - probably in a pretty energetic environment such as a black smoker - when conditions are correct. If so, that would imply that simple life would emerge virtually everywhere.

However, I'd also observe that for at least 60% of the history of our planet, it was microbes-only. There are good reasons for this - the lack of free oxygen being a major one. And this will probably hold more generally - the complexity of life will be limited by the complexity of the environment and the available energy flow. Earth, for example, has an extremely varied and complex environment, and the availability of oxygen and sunlight mean that there is a high energy flow. Whereas life under an icecap will have little diversity of environment and low energy flows; it may stay stuck at bacteria forever.

As far as intelligent life goes.. it could be argued that it's been possible ever since the mammal-like reptiles emerged >200 million years ago. So these could really be the rate-limiting steps to the Drake equation - changing the redox state of the planet to allow oxygen, followed by the dumb-intelligent transition.

An interesting observation is that around a red dwarf star, the first of those steps could quite possibly take 10s of billions of years. On the other hand, around a star hotter than the sun, it may be faster, but not fast enough before the star went bang. So we could be amongst the first.. and the 'golden age' of civilizations emerging from red dwarfs in their thousands lies many billions of years in the future..

By Andrew Dodds (not verified) on 14 Mar 2013 #permalink

- Life appears in the geological record on Earth basically instantly

Well, within a few million years, which is about as close to instant as the resolution of dating methods to that age get.

- The idea of life emerging as a result of random chemical interactions is essentially impossible.

That means you think life itself is essentially impossible. Something has to live to create something, but something can't live unless it's had a creator, is what you're saying. But that creator is essentially impossible since it had to emerge as a result of random acts itself.

Additionally, there is no conceivable stable state which is a ‘half-way house’ between simple inorganics and life.


And, since our definition of "organic" is "carbon based", any carbon-active catalyst is a half-way house between the two.

E.g. clays.

You cannot, for example, postulate complex-but-not-self-replicating RNA hanging around for millions of years. Not in liquid water.

RNA do replicate, though.

Your assertions seem based entirely on your incapability at biology. This is possible to rectify if you wish to. However, most "Creation MUST happen!" acolytes don't wish to.

Wow - I'm not a creationist ( or panspermia advocate). Would you like to reconsider your reply?

By Andrew dodds (not verified) on 15 Mar 2013 #permalink

Yeah, and Stalin wasn't a despot. He said so.

Would you like to reconsider your assertion I replied to?

How many planets are there

Ok, late reply. Although if any statement I make is automatically a lie if it tries to make you think it could be tricky.

The concept of an ocean full of complex organics giving rise to higher complexity is something I am arguing against, on extremely firm grounds - even the highest reasonable estimates of concentrations give a situation where hydrolysis rates would exceed any replication rate by many orders of magnitude.

Indeed, such arguments also rule out any notion of the 'long middle ground' of life formation. Which is good news for both astrobiology and any hope of replicating abiogenesis in the lab; there is simply no chance that a 'complex but nonliving soup' could persist for a noticeable amount of time, geologically speaking, so not only must abiogenesis be fast (again, geologically speaking) but it must follow a fairly set pathway.

The best hypotheses I've seen thus far revolve around the conditions at hydrothermal vents, which contain things like redox gradients, Fe-S complexes and clay minerals to promote mono-isomerism. Yet these environments persist for perhaps 10,000 years or less. Interestingly, any planet with substantial oceans on a silicate crust, even under an ice layer, will have 'black smokers' at some point.

So - unless the mechanism for abiogenesis relies on a very Earth-specific process (which I haven't even seen suggested) - then the chances are that it is both fast and near-ubiquitous.

By Andrew Dodds (not verified) on 19 Mar 2013 #permalink

"Yet these environments persist for perhaps 10,000 years or less."

why is it so hard to do some research before posting data?

from wiki: Strontium, carbon, and oxygen isotope data and radiocarbon ages document at least 30,000 years of hydrothermal activity driven by serpentinization reactions at Lost City, making the Lost City older than known black smoker vents by at least two orders of magnitude

By Sinisa Lazarek (not verified) on 19 Mar 2013 #permalink

"even the highest reasonable estimates of concentrations give a situation where hydrolysis rates would exceed any replication rate by many orders of magnitude."

Which is why the complexity was probably on the shores, not the deep ocean.

Please, stop arguing against strawmen, it's tiresome.

So what is your alternative theory? That some god-like-but-not-god-honest being waved their magic^Wscience wand and created^Wdesigned life on earth?

Sinisa -

I was going from memory. Say < 100k years. On geological timescales, near-instant..

Wow -

Calm down. As I said, I lean towards the black-smoker hypothesis (The idea of tidal pools is interesting, but you have to ask where the chemical gradients are in such a scenario).

My actual argument is this:
- The early appearance of life on earth points to rapid abiogenesis.
- It's also reasonable to argue from a chemical perspective that the process is rapid. Slow processes are actually harder to envisage.
- Therefore one should expect microbial life to be extremely abundant, assuming that the process operating on Earth was not a freak one.

I don't think that this is controversial. I would use it to predict life on Europa, IF Europa has a genuinely liquid water ocean in contact with a silicate mantle. Mars as well.. at least at some point in the past.

By Andrew Dodds (not verified) on 20 Mar 2013 #permalink

My actual argument is this:....$LIST

Then your opening statement was a complete waste of EVERYONE'S time.

- The idea of life emerging as a result of random chemical interactions is essentially impossible.

Is what you had as your bullet point in your opener.

Seems your argument as you are willing to say now never included that statement. If your actual argument was NEVER "the idea of life emerging as a result of random chemical interactions is essentially impossible.", then why the hell did you say it?

Just trolling?

actually.. the sentence "- The idea of life emerging as a result of random chemical interactions is essentially impossible." and " The early appearance of life on earth points to rapid abiogenesis" are totally opposite.

By Sinisa Lazarek (not verified) on 20 Mar 2013 #permalink

Which is why it might have been entirely troll.

Or it could be some IDer who found they weren't going to get any traction and have backed down and changed everything so they can then complain they've been done so bad by those mean religious scientistics.

So there are mega billions of planets that "could" support life (ie in a habitable zone). Do we have any way of telling which ones actually do have life. No. Or even what likely % of planets within habitable zones have life. No. So considering how far planets are from each other what are the odds that we will ever make contact with another living world ?? If we have to actually visit a planet to confirm there is life on it (and that may be necessary coz not all aliens will answer the phone if ye know what i mean) then this would be a project like no other, hopping from planet to planet, breeding & training generations of explorers on the way. Makes ye kind of wonder did some planet do this millions of years ago and they wound up here. heeheehee

There are possibilities.

For example, our atmosphere is VASTLY over specced on Oxygen. This amount of O2 in an atmosphere shows that there are processes like life on here keeping the atmosphere this out of balance.

Make as many comments about Universe and Planets as you could but, please, never inset the idea of "Lord" or "God" in this theme, it's very absurd and idiot. I hate very much someone - the Christians the most parts - use to impose their belief on the existence of their Lord or God in this discussion .

life is possible on other planet?and how many planets are currently discoverd? Tell me soon..

By janak sarwata (not verified) on 19 May 2013 #permalink

The religious get cheesed off (as a group, not necessarily as individuals) when atheists bring up "There is no god" in a discussion of the existence of god or where they are talking about it for any reason, so quite why they think it's fine to talk about there BEING a god when nobody is talking about it really eludes me, unless it's that A Crowley idea of "Do as thou wilt is the whole of the law".

But then they're sharing several other traits with Satanists then.

Very studious

I love these articles that summarize just how inconceivably huge the universe is.

You guys going off about which chemicals mixed to create life, how, and how long it took are all trolls. This article is estimating how many planets there are. Bugger off to your evolution forums. :)

By Lazy Alligator (not verified) on 11 Jun 2013 #permalink

I never knew that pluto has gone to rest because is to small. Well u are doing a great job.

That's totally mind boggling. I wonder why God would want to make so many planets.

One million trillion planets is not a lot to Him, since He is infinite in power, presence, wisdom, wealth, and knowledge.

hey friends i want to be a astronomer i will build a building to discover all the ten trillion planets in the universe see that is impossible but with god all is impossible

By airon charles … (not verified) on 23 Jul 2013 #permalink

A wonderful demonstration of the effect of psychedelics on the human brain there...

how many days does it take to get to planet & can u find emty land there?

By bright nnakwe (not verified) on 12 Aug 2013 #permalink

Planets or no planets God owns our lifes.keep searching

i like the way you present

By faiz anjum (not verified) on 18 Aug 2013 #permalink

Please u Christian guys respect the man's proffesion n work his doing,it's not the place to argue with people who do not believe in the Lord Jesus Christ.Please don't impose your God or Biblical knowledge Ethan i believe altough not really understanding what he say, gives scienctific and mathemetical explation of how vast the universe is.Please stay with the subject and give the man his for people who does not believe or see as we Christians i humbly apologise 4 my fellow Christian brothers or sisters if there is any.But in as far as life out there is concern i firmly believe they are there, they are however not as us, under free moral agency.YES U HEARD ME RIGHT THERE IS LIFE OUT THERE BUT NOT UNDER FREE MORAL AGENCY.IT MAY SOUND UNBELIVABLE BUT THE SOURCE IS NOT SCIENCTIST,IT SOUND CONTROVESIAL BUT I WISH TO AVOID ANY DEBATES PLEASE

I never see like that . very wonderful for me .

By than tun yin (not verified) on 27 Aug 2013 #permalink

if we can discover more than the speed of ligth there is a posibility that we can reach/go to the neareast star. this is a challenge to us to change einstien said that nothing can exceed the speed of light. discover more fastest rockets.

The numbers in the article are pure speculation. Physics indicates that massive stars could have several thousand planets.
Anyways, if life is rare as in only being found on quintillions of planets....intelligent life ever rarer and only on quadrillions...way too dispersed for much hope of us ever having any evidence of intelligent life 'out there'.

By Ray white (not verified) on 05 Sep 2013 #permalink

Re a comment on the Universe being 'old'. Actually it is still in its infancy. Regardless of what the fate of the Universe is, the scenarios play out over trillions of years. We're still in the first 1% of the Universe's existence.

By Ray white (not verified) on 05 Sep 2013 #permalink

i comment that it is possible to live in the new planet like mars or the new one discover above our planets 400000 light years away

By graeme limeric… (not verified) on 16 Sep 2013 #permalink

Wow! I impress with this

By DJ the rockstar (not verified) on 25 Sep 2013 #permalink

The creation of the universe is explained by astrophysicists as a widely accepted phenomenon,
Popularly known as "The Big Bang", According to the "The Big Bang" the whole universe was initially one big mass (Primary Nebula) then there was a "Big Bang" (Secondary Separation) which resulted in the formation of Galaxies, then divided to form stars, planets, the sun, the moon etc.

By Bassem Hussein (not verified) on 09 Oct 2013 #permalink

I would like to volunteer for the type of job Jodie Foster had in "Contact"... I don't mean the high-tech stuff; but the sitting on the top of a hill, with headphones on, listening to outer space. My kind of job!

Einstein's theory of relativity insinuates that nothing can move faster than the speed of light. This has recently been proved wrong and has been holding scientists back for years. Neutrinos have been proven to travel faster than light speed, therefore one of the most fundamental hypothesis of early science have been proven wrong.

@Cruiser: I'm so sorry that you're as far out of the loop as you seem to be. What was proven, more than a year ago, was that the precision timing circuit used by OPERA had a systematic bias due to an improperly plugged in fiber-optic cable, leading to an approximately 70-ns offset in their time-of-flight measurement for neutrinos from CERN to Gran Sasso.

If you're going to make wild claims about the overthrow of physics, you really ought to try to know the details of the work that led to that overthrow (or not). Otherwise, you end up appearing to be just another crackpot.

By Michael Kelsey (not verified) on 16 Oct 2013 #permalink

Well, the cable was loose and it was fixed under "any other business" but never actually proven to be the cause, it's just that the change COULD have produced that error in timing and that they've not been able to recreate it since then. The uncertainty is that they couldn't tell if it was done as the cable got fitted better or some other reason.

It's feasible and FTL is a bit of an amazing claim.

IMO they were right to push the note out there because a lot of people tried several ways of thinking

a) How could it be wrong (nobody figured a loose cable)
b) What would it men if it were valid

and it probably got a few more people interested in thinking about it that weren't really "into" physics any more. That some are kooks is merely a reflection of humanity.

@Wow #93: Almost. As I recall, what happened was that CERN did a short-pulse run (where OPERA could get spill-by-spill timing, rather than averages), and they saw the same offset. After discovering and fixing the cable, they had more short-pulse data where the offset went away. This was described in the updated version of their September 2012 preprint. I think that the before-vs-after effect is fairly conclusive.

By Michael Kelsey (not verified) on 16 Oct 2013 #permalink

Well, I never got to see a preprint of anything. The misalignment would have to be very small to create a capacitance of that size and the fittings are pretty much designed that it's pretty damn secure (this one was considered to be a knock that unsettled it). What I had heard was that they found a possibly loose connector and fixed that, then found it no longer gave the discrepancy. But maybe they'd done some testing to find that loose connector to know out of the probably ten million cables which were not acting to spec.

PS the "unclarity" was more along the lines of "we can't PROVE it, but it is both suitable and sufficient" allied with "and we can't get it to do that any more".

Which is good enough proof to get people sent to prison for capital crimes.

Ta very much.

Now if only my document viewer didn't decide to open it up with a default 32 point font...

OK, looks like the delay is dispersive medium rather than capacitive. That makes it a big easier to get a 70ns delay with a wonky connector.

Also appears thermal wobble changing the trigger level had a place to increase error bars.

I read quick. :-)

@Wow: Just saw all these replies :-) Thanks to Sinisa for the link back to arXiv! Yes, that's the paper, and I'll tell you that I shared your initial confusion about how a "loose connector" could cause a delay. I had to talk to some optoelectronics experts at my work to really understand it.

By Michael Kelsey (not verified) on 17 Oct 2013 #permalink

On a side note, Wow, congratulations.

Your comment #99 on this thread makes an even 4,000 comments for you. Although there are more than 30k approved comments, you are by far the most prolific commenter on my blog, and I wanted to congratulate you on your milestone.

I knew as soon as I heard the results that every crackpot on earth would glom onto the OPERA neutrino result and never let go. They'd assume that the preliminary result was the bonified truth, and never bother checking on it again (whereas I *wanted* it to be true, yet also wanted to know if it *really* was, so I payed attention to the ensuing investigation).

Hell, I still hear people using the Pioneer Anomaly as "proof" that all of modern physics is wrong.

Why would you check on the latest news when you already have your proof? The only difference it could make is that you find out you're wrong.

You spelt that right, yes, Ethan?

It wasn't "Millstone"? :-)

hehe... Happy Post Day Wow :)

By Sinisa Lazarek (not verified) on 17 Oct 2013 #permalink

It wonders me how the universe works because it's seintificly proven that we are not alone people don't realize how many different species there are in the the galaxy + there are over 50000 different planets

Never underestimate the universe with its powers

this shows that we humans are in a small part of the universe and also the superior of all creations by GOD. We have made researches on the planets outside ours why cant they(other planets) make some research about us?

By muhammed yaro (not verified) on 31 Oct 2013 #permalink

That's a lot to take in


By BRIAN LOVE (not verified) on 17 Nov 2013 #permalink

No, by definition, if it's infinite, we will never find out how many planets there are.

God doesn't fit anywhere in it.

And religion is not part of it any more than political affiliation is. It's something some humans decide to engage in, others self-identify with but otherwise do not engage in, and others ignore.


Brian, you use of capitals makes it uncertain as to whether you meant God or god, but your choice of the singular suggests the former. You may not be aware but there are thousands of postulated gods. Depending on how different sects may be before the become a different religion, there are even more religions. Whatever all or any of them may have done in the past, they are now largely constrained to a bit of minor tinkering in areas where Science can't yet look.


God fits nowhere into the scheme of things because the Christian concept of god is inherently non-scientific. To fit god into the scheme of scientific observation, you must find a way to put god's existence to the test. That is, you must find some observable part of the universe that would be expected to look different depending on whether god exists or not. If you actually make the observation, and the results indicate that god actually does not exist, you must be then willing to admit that god doesn't really exist. I suspect that you, and most Christians are either unwilling or incapable of doing this.

PS. I am assuming that you are coming from a Christian perspective here. I apologize if that's not the case, but my points pretty much hold up for any concept of god, not just the Christian one.

I strongly believe that earth is the only planet in the universe where such a wide range of life forms exists.

By dr john e w kingsley (not verified) on 22 Nov 2013 #permalink

good info

Beyond, beyond and beyond is what amazes me. There is no walls to the universe or outer space. If there were walls, what would be on the other side of those walls? Therefore, there is eternal time, unlimited space and numbers. This is a mystery.

By harold B. Peterson (not verified) on 07 Dec 2013 #permalink

hmn, wat a wonderful world

OMG. I Honestly Thought it would be written out like this, considering our universe never ends...
And Also You Think That Earth Is The ONLY Planet in the universe that has life!? Give me a break.

By Cheezaleezers (not verified) on 14 Jan 2014 #permalink

Also It is inpossible to know how many. If you took everybody's brain in the world (smartwise) and put it together it would not be able to get even the exact amount of inches of land in the world.

By Cheezaleezers (not verified) on 14 Jan 2014 #permalink

the universe is never ending
it cant explode
it cant just disappear
it will stay here forever

By Cheezaleezers (not verified) on 14 Jan 2014 #permalink

i want more information about this topic

By Collins Boateng (not verified) on 15 Jan 2014 #permalink

There's an entire internet out there with indexing of its contents available for you to use.

If you wish someone else to do the work of collating and explaining it, then there is a vibrant adult education system you can apply to use.

What are the two things that are faster than the speed of light?

The creation of the heavens and earth is greater than the creation of mankind, but most of the people do not know.

Of course we have no idea how many planets we have in our solar system. I was just wondering if anyone would be dumb enough to put 13 (Our main eight plants and our 5 dwarfs)

i'm an amateur astronomer and i know the 10 to the 24th power is in fact 1 septillion and since i do understand large #'s our known universe is approximately 15 billion light years which translates to around 90 septillion miles.

i also know that it won't be in my lifetime which i hope is another 25-30 more years that man will be able to fly the speed of light. it's called einsteins theory of relativity in which the close you go towards the speed of light the slower time gets,

this theory has actually been proven experimentally, it's called time dilation. i believe star trek calls it warp drive.

" La scienza non deve aprire una porta al sapere ma chiuderne una all' ignoranza."

" Science doesn't have to open knowledge's door, but close ignorance's one. "
-Galileo Galilei

The answer is 42.

By Mick Dundee (not verified) on 31 Mar 2014 #permalink

Yes, Mick, but what's the question? :)

i need to know more about planet and how have bee discovered, with there picture

By CHICHI AKEN JOHN (not verified) on 09 Apr 2014 #permalink

Fantastic topic and amazing to see a truley global debate taking place. I only hope that future exploration of what is potentially "out there" and how to get to it will only further unify what we have "on here " and how we make the most of it.

It is funny that the estimated number of planets in the observable universe is close to one mole (Avogadros constant)

Less than imagine

good evening, so can one live on the other planets and how does it benefit man and in what way does people find their way to the planet , if i may ask what sort of things can be find there and is it true that the planet is only nine and why do they say that .

By okuoba nana akomeah (not verified) on 13 Jul 2014 #permalink

Wow great photo's....... the univers of all human and substance particle depend in gravitational force.

By AAMER RAZA KHAN (not verified) on 22 Aug 2014 #permalink

You know the largest crater on the moon is the South Pole - Aitken Basin . it is 2,240 km in diameter and 13 km in depth . my Aim is Scientists of Paleontologists .

By Jayesh Shivhare (not verified) on 29 Aug 2014 #permalink

in the other planet in other solar system . . there's a posibility that there are other people or living things or anyone who are breathing Living in other planet on the other solar system ?

how many planets in the universe

By shubham singh (not verified) on 22 Oct 2014 #permalink

I have a question: Isn,t it possible that smaller than the smallest stars form a without light mass by gases as the stars formed ,if so there shoud be milliards of without light huge masses that may give an answer to the weight and noise of the whole universe .

The number of planets that exist is infinity.. If infinity is defined we can say it is equal to number of planets in the universe.

By bkmahatma (not verified) on 09 Jan 2015 #permalink

awesome article

The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

Original estimates
There is considerable disagreement on the values of these parameters, but the 'educated guesses' used by Drake and his colleagues in 1961 were:

-R* = 1/year (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative)

-fp = 0.2-0.5 (one fifth to one half of all stars formed will have planets)

-ne = 1-5 (stars with planets will have between 1 and 5 planets capable of developing life)

-fl = 1 (100% of these planets will develop life)

-fi = 1 (100% of which will develop intelligent life)

-fc = 0.1-0.2 (10-20% of which will be able to communicate)

-L = 1000-100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)

Inserting the above minimum numbers into the equation gives a minimum N of 20. Inserting the maximum numbers gives a maximum of 50,000,000. Drake states that given the uncertainties, the original meeting concluded that N ≈ L, and there were probably between 1000 and 100,000,000 civilizations in the Milky Way galaxy.

WOAH! So I decides to google... "How many stars are there in the universe?
"To answer “how many stars are there,” we must limit the discussion to what we can observe. Astronomers estimate that the observable universe has more than 100 billion galaxies. Our own Milky Way is home to around 300 billion stars, but it's not representative of galaxies in general."

So I said screw you google. Ill make my own rules! By generalizing the Milky Way Galaxy civilizations and multiply that by 100 billion galaxies, so I could get a rough guess on how much intelligent life, could possibly be out there. (Correct me if I did this wrong)

So 50,000,000 civilizations X 100,000,000,000 Galaxies in the universe X 300,000,000,000 Stars in the milky way (as a general guideline) = Rough Estimation of intelligent life in the universe.

The conclusion,


Usjebxudiwowndhuxd7hej3so blaaaaaaah!

Thats 1.5 Nonillion (30 Zeros) of intelligent civilizations. The real number could be double, or less than half.

Either way, weather you believe it or not, life exists outside of our mother earth. And very abundantly.

Now after reading this article (ive copied and pasted my formula) that NOW, that number could be quadrupled) I even heard there could be as much as 500 billion galaxies

"Either way, weather you believe it or not, life exists outside of our mother earth. And very abundantly."

I disagree. We can estimate how many planets are in the universe, but we have really no idea of really knowing the probability that complex life - let alone intelligent life - evolves on any of them.

Drake equation is nothing but guesstimates.

10 with 24 zeroes isn't all that many, actually. Think about It that way: you keep on dividing it by 100, you only need to do this 12 times to get down to 1. In other words, if a planet has to meet only 12 criteria to allow life, and there's a 1% chance of meeting each of this criteria, then it's quite likely Earth could be the only winning ticket in the universe.

And there's plenty of factors. If we had no Moon (that helped to stir the primordial soup with its tidal influences), or if there was no Jupiter and other gas giants (they shield us from collisions with objects entering the Solar System by intercepting them), or if Earth's axial tilt wasn't mere 23 angles but more (meaning we wouldn't have mild seasonal climate transitions), or if the orbit wasn't stable, or...

And even on Earth, evolution had to be "rebooted" several times (five mass extinctions, dinosaurs weren't even the biggest one) before intelligent organisms happened to evolve.

And even on Earth, evolution had to be “rebooted” several times

Which was done by primitive organisms, WHICH ARE STILL LIFE.

Again, the difference between life as biology and life as we parochially percieve as "complex organisms".

DO NOT place an unstated assertion on someone else's statement without having investigated what they may have *correctly* meant.

You are one ugly bastard...


Actually, the more modern origin-of-life theories put the origin around hydrothermal vents (and there are some compelling chemical and energetic arguments to back this up). If this is true, then we should microbial life emerge very quickly indeed on any body that has a hot rock/liquid water interface.

Moon forming impacts would appear to be fairly common in the formation process of Earth like planets.

This does not mean that Earths are common - but it's not freakishly uncommon. The longest and possibly hardest step on Earth as far as intelligent life is concerned was the changes in geochemistry to allow an oxygen atmosphere - which took several billion years. Once that atmosphere was present, we went from primtive Chordates to humans in just 500 million years - barely 10% of the planet's history.

Which is interesting. The bits that people emphasize - origin of life, and emergence of intelligence from worms - both happened quite quickly, geologically speaking. But inbetween we have ~3 billion years of microbial life. Which means that in all probability, there are a LOT of earth-analogs out there that have plenty of microbes; especially those around smaller stars that may have slower photosynthesis.

(Those around larger stars may get toasted before they get oxygen)

By Andrew Dodds (not verified) on 13 Feb 2015 #permalink

Hi,I think that human being on earth never will be able to travel to other solar systems of our galaxy but manmade robots will be able to make future wave form robots that not only make huge changes in our galaxy but also in whole universe in next 20 milliard years.

Hi,I think that human being never will be able to travel to other solar systems of our galaxy but manmade robots will be able to make future wave form robots that not only make
huge changes in our galaxy but also in whole universe in next 20 milliard years.

AHuman being on earth with highest technology in universe from big bang theory till now.I am almost sure that, human being on planet earth is the only inteligent one that reached to electrical technology in universe even with more than1000000000000000000000000 planets;because of the following reasons:1- we know that life period in our planet is more than 3 milliard years. 2-we know that our technological improvement includes two periods: a- before electrical technology b- After electrical technology.3- we know that our milky way galaxy is more than 13 milliard years old and it's diameter is only 100000 light years.4-suppose that just a few planets in our galaxy or in our nearest galaxies had the same conditions as like as our planet earth just one to five milliard years before our planet earth and reached to electrical technology 1 to 5 milliard years before us;then,didn,t they send their electrical technology robots around most stars of our galaxy ;so,we should receive intelligent made signals from some of those phosil robots(the programmed robots that had used stars' energy to rebuild or reprint the same as they were made ) to rotate around all stars of our galaxy .4- If we accept that we can send missels faster than comets in space in our solar system ,so if we add the time that a comet with life came toward us plus more than 3 milliard years (life period on earth)ago,and the higher possibilities for more comets with life of the same solar system encounter to it,s nearest planets that had almost the same conditions for life as like as our planet earth so we should have recieved their electrical technology signals when we learned how to get signals from space around our planet,I am also almost sure that the primitive life began on our earth and life didn,t come by comets to earth.

;because of the following reasons

No we don't. those reasons do not support your claims as a form of proof, they are merely assertions without validity.

please how many planets are there in our iniverse.can someone give me the answer???

i think tha there are 10 to 24 planets in the universe

There are actually 50 sextillion, or 5×10(to the power)22, or 50,000,000,000,000,000,000,000 planets in the universe ( not our solar system). This is just theory and approximation, astronomers have never observed all of them.

By Adam Fattal (not verified) on 29 Mar 2015 #permalink

Shape of universe. I think that accelerating exspansion of universe is constantly equal to pi (3/14*radius)and the shape of universe is constantly spherical and increases(accelerates)in it's spherical form,and the reason is not because of dark energy but because of rules of gravity in matter. We see that in our planet earth the heaviest elements are in core and the lightest elements are in atmospher in gas form and gravity causes the shape of our planet remain almost spherical,hence in universe gravity should cause that the biggest blackhole locate almost in the center of universe as a core and smaller galaxies to incline toward the outer sections of universe in an almost spherical shape as our planet is almost spherical shape.

I think that accelerating exspansion of universe is constantly equal to pi (3/14*radius)

What are the units?

Pi *radius in power 3 (3/14*radius in power 3) and radius is apparentlry between 7 to 14 mllliard light year at least.

wow its so amazing
God is able
do you think about our universe....i have world to define this.
its undercover and unclear for us.
but its matter in God power.
because God create our universe

By ephrem elias (not verified) on 15 Apr 2015 #permalink

god is a fiction.

If anyone thought it existed,they wouldn't bother with jails, courts, and so on, they'd just let god sort it out.

But you don't, do you.

Because even you don't think it exists, and you have to do its work here and now.

Just blather on about it on a religious site, retread.

No end, there are more..... and more....... and more.

By Sarath Prematilake (not verified) on 22 Apr 2015 #permalink

Thats interesting

Yea God is just so amazing creating all this wonder and beauty! WOW

By floatingwhiteshadow (not verified) on 22 May 2015 #permalink

What god?

*Which* god?

Thank Vishnu? Or is it thank Marduc? Thank Chronos? Thank goodness they're all equally likely to be right, therefore all wrong.

Thank god? Nah, I'll chalk it down to reality rather than the presupposition of a myth.

I think that our universe is spherical and it is rotating and it is moving because of the following reasons: 1- we know that logically we have unlimitedtime and space. 2-we know that we have a universe with gravity and matter now. 3- we know that when something changes to somthing else once ( here our universe) in a limited place and time ,it could be repeated and it will be repeated many many times in unlimited space and time ,so there should be many many universes around our universe. 4-we know that in our universe everything is moving and our universe is moving too. 5- It is moving from one place to another place because of interactions between it, s gravity and the gravities of other universes . It is rotating because it contains different gallaxies with different gravities and densities in different parts of it, so when our universe was moving in space, the gravities of nearest universes interacted with the more density parts of our universe and caused our universe to begin to rotate .THE second thing that causes our universe to rotate is by the bigger gallaxies that flew away from the surfase of most gathered gallaxies witch remained and made the main mass of our universe and these bigger gallaxies turned around main mass gallaxies freely and usually faster than the inner mass gallaxies in an elleptical form.7- It is increasing it,s expansion because of a- eccentric power while rotating b- the gravities of other universes around it.8 - the almost unique accelerating expansion of our universe is for it,s rotation too.

"1- we know that logically we have unlimitedtime and space."

This is absolutely not the case.

Logically, it must be limited. Our best models would support a limit.

Given that your claim is based on the propositions you hold and the VERY FIRST ONE is false, this is sufficient to indicate your conclusion is faulty.

Just as a claim of "all swans are white" is disproved by the existence of a single black swan.

The reason that I think logically time and space should be unlimited : 1-suppose that big bang theory is a fact in forming our universe and it begun at a specific time and suppose that forming our univrse is the same as formig the life on earth 2-both of them need duration of time and need space(place).3-both of them are the result of changing of something to something else that were absent in their new form.4-Can we imagine that before forming the life on earth we had no passing the time,surely not ,and so we had passing the time forever before forming of our universe and so about the place(or space)

None of those suppositions lead to your stated conclusion. And #2 and #3 don't actually pertain to the theory you are supposing to be correct in #1.

And for #4, the formation of life on earth was several billion years after the big bang.

Go check wikipedia for the big bang and read up on the popular explanation of it.

I also note that these are a very different list from what you tried earlier.

Give what you've posted so far, it may be worthwhile to try a different tack to see if there's something constructive to go through here.

Lets go right back. Does it matter if space is infinite and time infinite at all? What would that being correct be able to do or preclude that you wish to find this to be the case (or not)? E.g. "It makes more sense to be if it is infinite" isn't a reason for it to be so: the universe doesn't have to make itself understandable to you to exist. But if there's some feature that you think it would get as a consequence, then maybe looking at that feature would be more fruitful.

It may be that that feature is known to exist by other means. Or known NOT to exist, therefore evidence of a limited space/time for the universe. Or it may be the feature doesn't matter. E.g. "Well, how could the universe form if it had to start?". There are answers to that query.

At the moment, though, you have made claims and post-hoc raised excuses to support that claim, none of which appear to be either valid or supporting your conclusion, so all that's left is to say "It doesn't work that way". Which appears to make you think "I need to find a different explanation of why the universe is infinite", and that merely wastes everyone's time and effort.

Hence my suggestion we find out what it is that you need an infinite universe for.

Help me answer this question. Mention three planet found in the universe?

By Yunusa shekuru (not verified) on 30 Jun 2015 #permalink

Apparently one of the most important puzzles in cosmological phisics is dark energy while our universe before big bang was a strong typical of dark energy for it's sorundings and this can be one more reason for existing multyverse as dark energies for expanding our universe and for causing of begining of our universe's big bang by the sum of their whole gravities.

Well, no, you won't. It's just how to google for images of the night sky, and that's it.

Somebody is fluffing up their google ranking (and therefore payment)

this really answered my question! Thanks so much!!!!!

it hunt my head

By ewurum uche22222 (not verified) on 24 Nov 2015 #permalink

I loved the article, and the approach to coming up with the estimate. Do you have some sort of academic source (such as a peer reviewed paper) that has an estimate I could quote for research purposes? Thanks!

try doing some research for your research purposes...


it look so creative. with power of wisdom

thank you so much, may you please do an answer to 'how many stars are in the pillars of creation' AKA the hand of god.

again, thank you ever so much

yours sincerely, space girl

By space girl (not verified) on 09 Jan 2016 #permalink

The pillars of creation aren't known as the hand of god.


Maradona's use of his hand to score a goal in the world cup was. But there is only one star in that. Maradona himself.

And since the area is only part of a larger nebula and that it is a dark obscured nebula, therefore not possible to look inside, all counts of stars in there would be guesses.

Given the longest part of the region is four light years across and it's therefore not liable to be more than 16 cubic light years (and very likely to be less than half that), comparing with other dense open clusters would indicate something less than a dozen stars in there.

Please refrain from using "AKA" which stands for "Also Known As" when it isn't also known as the asserted name. This is deception. Not a good way to start asking for answers.

C'mon Wow - there's no need to accuse other commenters on trying to deceive people when they've just made a simple mistake.

The 'Hand of God' is a well known name for the pulsar wind nebula B1509. Here's a NASA article on the subject:

It's an easy enough mistake to make to conflate the two fairly similar images - the later HST image of the 'pillars' do look like a hand as well.

A word of advice -
If you meet someone in public who is fascinated by the subject but happens to mix up two pictures, don't make the mistake of rebuking them for deception. It may be considered incredibly rude and unproductive, as well as, perhaps ironically, deceptive.

"C’mon Wow – there’s no need to accuse other commenters on trying to deceive people when they’ve just made a simple mistake."


But it has to be that it IS just a simple mistake and not deception for this to apply here.

You should not accuse other people of malice when they merely have concluded differently from you.

"It’s an easy enough mistake to make to conflate the two fairly similar images – the later HST image of the ‘pillars’ do look like a hand as well."

It is not known as the hand of god, though. This is plain fact. And that didn't show any reason to believe it was.

MOREOVER, there was absolutely no need for calling it that. So why was it called that? To interject god into a science thread? Why was it said OTHERS in sufficient numbers called it that so it was "AKA"? Argumentum ad populum? And this is about how many planets are in the universe, not how many stars, so why bring up number of stars at all? And given we have thousands of such stellar nurseries in our solar system, and additionally that this one here is not an actual separate nebula, but a very small section of a much wider known one, why was this one specific cherry picked to ask about? To bring up the pillars of creation (which won't have any planets yet, most likely) and thereby also bring up god, in a science discussion again?

A word of advice, there are thousands of godbotherers who cannot let anyone else believe differently. Whether christian, muslim, bhuddist or scientologist, they will kill people for not believing like them. And just because they see god everywhere doesn't mean that their fascination with it should pollute every discussion in the world. Doing so is incredubly rude and unproductive as well as, ironically, deceptive.

Not to mention proffering without any proof or conjectured evidence for being rude, unproductive and deceptive such as you do here is, ironically, all those negative things. Maybe you should wonder if you're building planks in your own eye so that you can be a hero defending the weak for perceived splinters in other people's vision.

I would ALSO note, Marc, that it was entirely ignored that I not only gave the best answer, but also the derivation, so I answered the query.

However, being helpful to someone posting offtopic is unimportant if you're looking for crimes committed by others to persecute.

Going online vigilante is rude, offensive and unproductive.

We're back to that again, aren't we? Maybe there's a problem with starting off with "rude" and building up under the "rule of three" or "rule of repetition" in rhetorical techniques here. Because "rude" is subjective,and therefore not something that can be defended, since it requires the accuser to accuse the other of error without knowing the thoughts of the accuser. Feel free to think "Well, that's rude" then fuck off. Irony.


By Sebastian (not verified) on 01 Feb 2016 #permalink

@Phil Shafer, #8 comment

i too have been thinking about how to visualize such a big number so how about this :

10'24 planets....

If you covererd whole the land area of planet earth with a grid of squares 0.01mm x 0.01mm (so that there are 10,000 in each mm2) you would have approximately the same number of squares in the grid as planets in the know universe....

1mm2 = 10,000
1cm2 = 1,000,000
1m2= 10,000,000,000
1km2= 10,000,000,000,000,000 (10'16)
1million km2 = 10,000,000,000,000,000,000,000 (10'22)
148million km2 (earth land area) = 1.48 x 10'24

There are 13 planets in our universe.. Today there are 9 that we are 100% sure of .. The rest will be discovered soon ☝️:)

Apparently 99/85%of our solar system,s mass is our sun and the planets and the rest are just less than0.2% ! Doesn,t the visible tails of spiral galaxies which are apparently more than 10%mass of the whole mass of a spiral galaxy guide us to this result that the primitive cloud that was making our solar system,the percentage of cloud which separated from main mass (sun) and made planets was much more than 0.2% and even more than 10% and went enough away from our sun by eccentric separation speed more than the eccentric separation which our solar system,s remain planets had and went and made wandering giant masses and continued their way to reach to another solar system,s gravity in their way and were accepted as guest planets for those solar systems.

Aren,t the stars of most binary stars the result of joining of two wandering stars which each star was separated from primitive cloude of a super massive solar system,s eccentric separation of poly star which left by the primitive speed which their separated cloude had gotten not to remain in the limitation of their poly star solar system and wandered away till reached each other and made the binary stars.

No, most stars are multiples because the gas cloud that formed the stellar nursery holds thousands of solar masses of gas to collapse, and the collapse necessarily causes the volume stars can form in to be limited.

So it's far far more likely that stars will form randomly close enough to each other to bind gravitationally than so spaced out that they do not interact closely.

Just like it's more likely to get a run of three consecutive numbers in the lottery roll of six numbers of 49 than to get no sequence at all.

If our solar system,s primitive cloud was 100 times larger didn,t we have a big central sun and many shiny(star form )planets orbiting around it.

Apparently most physicist accept that big bang theory has the first acceptable posision among different theories in forming our universe with using of telescopes and other things and accept that these trillions*trillions huge masses practically can collapse as small as a point ,and the passing the time in differrent parts of this expanded universe changes ,in my opinion inside of our universe and outside of our universe mightly have a constant (time passing) and what we consider as a different in passing the time might be only the different in dimension of changing matter and antimatter and what we observe as passing the different time in different parts of our universe be just different form of changing in differrent conditions of matter and antimatter in different parts of our universe.

In our very big universe there must be milliards of systems that their primitive cloud were less than smallest stars and have made the without shining central terestral masses with many orbitals with about our moon or smaller masses which turn around them and mightly smaller sattelites which orbit around their moon size masses in invisible part of our universe .what is the name of these form of systems and their central terestral masses and their orbital masses and masses which orbit around their orbital masses.

I think that in our universe, all sollar systems which have about the same size of our solar system have averagely a host planet or a host satellite In their orbitals.

P.s.and an averagely host planet or host sattelite crashing in their solar systems.

Do you ever listen to anyone else, or is this just generated internally and vomited out for personal gratification?

I subistitute the words,,guest planet and guest sattelite instead of host planet and host sattellite in my two previous comments.

,,Do you ever listen to anyone else,, I would be thankful if you read comment (204) accurately and then give me your new answer.

(To wow) I would be thankful if you read comment (204) accurately and then give me your new answer.

Sorry, please execute your own reading. You asked a query in 205 and it was answered in 206 and never acknowledged nor changed the meaningless burble spewed up by your keyboard.

Indicate there's some vague hominid reasoning going on on that side of the internet.

Sorry, please execute your own reading. You asked a query in 205 and it was answered in 206 and never acknowledged nor changed the meaningless burble spewed up by your keyboard.

Indicate there's some vague hominid reasoning going on on that side of the internet.

Else this is proving that you've nothing to say in 204 and reading it will not advance a damn thing.

I am not a phisicist but I think that there is a direct relationsheep between dark mater and inflation in our universe,so that if the speed of inflation in our universe was more or less than now, then we had more or less dark mater (invisible mater) with respect to visible mater. meanwhile I apologize if my comments are not enough understandable ,it is because english language is not my mother language.

"I am not a phisicist "

Plainly obvious.

"but I think"

No evidence of this.

"there is a direct relationsheep between dark mater and inflation in our universe,"

And definitely none for that.

Tell me, do you just make shit up and then think it's right? If so, what limits do you put on it, if any? If not, what ARE those limits, why do you apply them, and how?

And if your native tongue is not English, then talk in the language of maths which is far more precise and accurate. Or discuss them in a site that does use your native language, not here.

Babbling about half-thought (if that) ideas in a language you don't understand on a subject you also do not understand will only ever result in you looking like a clueless moron.

If you ARE a clueless moron, then this will not phase you in the slightest. If you AREN'T, then this is why you will need to firm up your ideas elsewhere where at least the incomprehension of language doesn't interfere.

this is something beyond our imagination humanity can only understand the secret of this Universe if we can only travel like the speed of the light gazing the skies and using telescopes will not help

By Ibrahim boodbood (not verified) on 08 May 2016 #permalink

I feel lonely in this universe I would like to have some friends in the milky way galaxy

By Ibrahim boodbood (not verified) on 09 May 2016 #permalink

Although humanity has been living on this planet for several million years we had reached great success we put foot on the moon so another million years or so where do you think that human will reach I am sure that they will reach where Kepler is now hunting planets in this nearest constellation but please you must know the difference between cosmos time and human time in cosmos time several million years are only matter of days in human time it is like doomsday

By Ibrahim boodbood (not verified) on 12 May 2016 #permalink

I ultimately believe that human beings will conquer the universe and they will inhabit all those life supporting planets out there , we are at beginning of the journey , our lives will not be confined on this mother planet , it will expand , expand in the whole universe . Humans navigation history taught us that , it never stops in a time. That journey may take a billion year , for cosmos time that is not too far . But my big worry is if humanity will survive on this planet for another billion year . I wish if I had lived after a billion year to witness that great evolution of Mankind.

By Ibrahim boodbood (not verified) on 13 May 2016 #permalink

Do not worry this universe belongs to you and waites you

By Ibrahim boodbood (not verified) on 13 May 2016 #permalink

Our true success depends our knowledge to space

By Ibrahim boodbood (not verified) on 13 May 2016 #permalink

With such a fast universe with so many galaxies and so many solar systems in each one, I don't believe for one minute that the big bang resulted from nothing! that to me would be more bizarre than believing in Father Christmas!

Is true that humanity was created from star dust ?

By Ibrahim boodbood (not verified) on 21 Jun 2016 #permalink

Is it true that humanity was created from star dust ?

By Ibrahim boodbood (not verified) on 21 Jun 2016 #permalink

@Ibrahim boodbook #227, 228: Yes. _Everything_ is made of stardust. Only hydrogen and helium were formed in the early universe, and condensed to become the first stars. All other elements were formed either during the lifetimes of stars, or in supernovae at the end of stars' lives.

By Michael Kelsey (not verified) on 21 Jun 2016 #permalink

Ibrahim boodbood:
“Is it true that humanity was created from star dust ?”

Well, Michael Kelsey says, YES!
Basically, the Big Bang banged, stars were formed…..
and the stars became you!
[At least that’s HIS story. And he’s sticking to it.]

Everybody is a star, Ibrahim.
But perhaps more in this way, I’d like to think:

By See Noevo (not verified) on 21 Jun 2016 #permalink

Just mind blowing. Caleb Scharf wrote a book called The Copernicus Complex which I massively reccomend if you enjoyed this.

By Aidan McLure (not verified) on 10 Jul 2016 #permalink

"I don’t believe for one minute that the big bang resulted from nothing! "

Who cares what you "believe", Dan.

Peter Sutcliffe "believed" Jesus Christ spoke to him and told him to kill those women.

ISIS murders "believe" Allah is telling them to behead those heathens.

It's a hell of a lot more believeable that the universe came into existence out of nothing than something that can create universes came out of nothing first.

I know we don't like to hear words like "never" when it comes to Science. But people some are you talking about traveling 186,000 miles per SECOND. for me its hard to see it will get accomplished, its just not the speed alone. There are so many other variables.

Well, we already have science saying "we will never reach the speed of light", even without any other variables.

So, OK, but what is the relevance of these other unnamed and unformed variables? Do they even exist?

To: wow

Forgive me for saying/asking but you strike me as an Atheist. Personally i can't understand that. Not to be a pessimest but mandkind is probably closer to the end rather than begining of existence. My point here is mankind 'in a million years' will never reach the intelligence level to ever come close to understanding the universe let alone life itself. Frankly who are you to suggest god doesn't exist or 'you can't prove it'. By you own relegion 'science' it's incalcuable to explaine the universe in any other way. That to me seems as improbable as saying life is not existent anywhere else in the universe.

Forgive me if i've given any offence it is not my meaning.

To the author: thank you much for the analysis as you've answered some questions i've had.

In every minute of my life I always think and eagerly waite what is the amazing real story that will come out from this universe i have never admired anything else than universe . most people seem never mind this

By Ibrahim boodbood (not verified) on 05 Aug 2016 #permalink

In every minute of my life I always think and eagerly wait what is the real amazing story that will come out from this vast universe I have never admired anything else than universe I always imagine and accumulate this vast universe in my small mind but most people seem never mind this.

By Ibrahim boodbood (not verified) on 05 Aug 2016 #permalink

Sometimes I feel powerful that I can exploit the universe and i can control it like a property and sometimes i fell that i am weak and only the product of small particles of dust mixed with water and will immediately go back to dust and become another form of energy that will be beneficial to the life existing above earth .

By Ibrahim boodbood (not verified) on 05 Aug 2016 #permalink

Every thread (not sure if that's the right word) has the subject changed to basically religion and inconceivable theories which are essentially different versions of "I don't understand the subject so someone must have done it i.e. God".

Who changes the subject to this every time?

The fucking Godbotherers. EVERY TIME. Basically anything on this site that is to do with universe theories that is older than about a day will have a Godbotherer in it. LITERALLY.

If you are a Godbotherer, then leave this site. Nobody here wants to hear your deluded speeches that basically say Goddidit. NOBODY CARES. You can believe what you want but just don't come to this site because it has nothing to do with religion.

space is coolllllllllllllllllllll

i am shocking to listen listen that scientist are searching planets like earth but it is not necessary that life can be possible on earth for its situation it may be that another planet it is not necessary to take oxygen for life and water for life if on earth plant will take carbon-dioxide and release oxygen than at other planet aliens may be take nitrogen for life it will be possible, scientist will search every planet for life not should be like earth only

"Forgive me for saying/asking but you strike me as an Atheist. "

Everyone is to better than 99.99% an atheist.

"Personally i can’t understand that."


" Not to be a pessimest but mandkind is probably closer to the end rather than begining of existence. "

Well, that's no reason why you shouldn't be able to understand someone being atheist. It doesn't even make sense.

What is puzzling me is up to now that there is no real answer or understanding the mystery of this universe , but I hope that the unthinkable of the present time will be thinkable and easy for the man who will be living on this planet for another million year . Technology was only possible for human beings after staying here for several million years .

By Ibrahim boodbood (not verified) on 04 Nov 2016 #permalink

hi this is amazing to hear that there are hundreds of planets in the universe

By Jemma King (not verified) on 31 Jan 2017 #permalink

Well, we can always thank science for all these marvelous discoveries.But one thing remains the same,"our little mind is too small to comprehend how big the CREATOR is'.
you may call him,God,Allah,Jah etc.
and this is the God we are messing with...........?
we're fucked up..
When i see all these thing,it motivates me to worship the creator.
I was watching an Islamic video the other day,and it said,He is the creator of Seven Heavens,all what we are seeing is within the first heaven,there are 7 sevens.

No, Joshua, I created the universe. Want proof? Stick your head out the window. See all that stuff there? Think it made itself? No? That's because *I* made it!

But I can tell you, as the creator of the universe and everything else, there aren't seven heavens. It's just a metaphor.


But if you want one, you go ahead and build an everything yourself. See how easy it is, huh? THEN you can start complaining about things going wrong. It's not easy being the creator of all reality, you know.

The best is yet to come the time is fives to twelve, open your mind people and think out of the box.
I look at the Solar System of Planets and I live within that moment of each day seeing something new every day.
Keep searching there no end
James Willams

By James Williams (not verified) on 07 Apr 2017 #permalink