Asteroid #2 down; on to Asteroid #1!

esiegel — Thu, 30 Aug 2012 15:59:44 +0000

"I have announced this star as a comet, but since it is not accompanied by any nebulosity and, further, since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet. But I have been careful not to advance this supposition to the public." -Giuseppe Piazzi, discoverer of Ceres, the first Asteroid

Out beyond Mars, but not quite out as far as Jupiter, a collection of thousands of rocky objects, ranging in size from pebbles all the way up to the size of Texas, lies the asteroid belt.

Image credit: David Minton and Renu Malhotra.

While the very first asteroid was discovered way back in 1801, with many thinking it was a planet, it was quickly discovered that there were many small, sub-planet-sized objects in between Mars and Jupiter.

Image credit: wikimedia commons users Vystrix Nexoth.

By 1849, there were 10 objects known, with the largest being Ceres and the second largest -- at least in terms of mass -- being Vesta. As even Ceres is minuscule compared with our Moon (shown in grey, above), none of these objects could rightfully be considered planets, and hence we now consider the entire collection to be the asteroid belt. While the combined mass of every asteroid is just 4% the mass of our Moon, Ceres and Vesta alone are estimated to make up nearly 40% of the mass of the entire belt.

Image credit: NASA, ESA, L.McFadden, J.Y.Li (UMCP), M.Mutchler, Z.Levay (STScI), P.Thomas (Cornell), J.Parker, E.Young (SwRI), C.Russell, B.Schmidt (UCLA).

Because of their small sizes and their incredible distance from us, even these two most massive asteroids -- about the size of Texas and Arizona, respectively -- barely have any discernable features, even when imaged with the Hubble Space Telescope, as shown above.

But these asteroids are very different from our Solar System's other rocky worlds. For instance, they're made up of different elements than we are, their surfaces are very, very old, and they're the closest things we have lying around to protoplanets: the building blocks of our Solar System's rocky worlds that haven't been a part of the inner Solar System in over 4 billion years.

Image credit: H. Chang from National Tsing Hua University in Taiwan.

But they are still around in the asteroid belt; Ceres and Vesta are, officially, protoplanets that failed to coalesce into full-on planets. So if we wanted to learn more about the formation of rocky planets in the Universe, that would be the ideal place for a mission. And -- wouldn't you know -- we've got just such a mission going on right now: say hello to the Dawn Spacecraft!

Image credit: NASA.

For over a year, now, Dawn has been in orbit around Vesta, taking more than 28,000 images, mapping the surface in 3-D, and learning more about this distant protoplanet than any such object ever before. Just a visual comparison of Dawn's true-color composite of Vesta with the one from Hubble should stop you in your tracks.

Images credit -- Dawn view: NASA / JPL / UCLA / MPS / DLR / IDA / color composite by Daniel Macháček; Hubble view: NASA / ESA / STScI / UMd.

There are some amazing features we've found on heavily-bombarded Vesta, some of which are completely unique -- as far as we know -- to our Solar System. Perhaps the most striking is the impact basin over 300 miles (500 km) in diameter on its South Pole, with a mountain over 14 miles high in the center!

Image credit: NASA / JPL / UCLA / MPS / DLR / IDA.

Known as Rheasilvia -- named after the mother of Remus and Romulus -- this crater is 90% the diameter of the entire asteroid, and the wave-like ripples you can see throughout Vesta clearly originated from this impact! Perhaps only two or three other asteroids in the entire belt would have survived an impact like this; all others would have been destroyed.

A false-color topographic map that I've managed to track down should really show you just how gigantic this feature is.

Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.

The impact responsible for this also happened relatively late in the Solar System's history: while most protoplanetary collisions were done more than 4 billion years ago, Dawn discovered that this impact on Vesta happened just 1-to-2 billion years ago, which is very late for the Solar System. The great impact also created this remarkable system of trenches along Vesta's equator.

Image credit: NASA / JPL / UCLA / MPS / DLR / IDA.

These equatorial trenches are many hundreds of kilometers long, which is gigantic considering the entire asteroid is only some 530 km in diameter! You may also notice that, in addition to the normal light-and-shadows you see over the terrain, there are lots of materials on Vesta that are simply intrinsically dark. You can really see this if you look at the "Snowman" on Vesta.

Image credit: NASA / JPL / UCLA / MPS / DLR / IDA.

This is still a major mystery: where did this dark material come from? One leading theory is that it came from beneath the surface, and was kicked up unevenly by the impact that created Rheasilvia.

What's kind of remarkable is that tiny "Vestoids", or rocks originating from Vesta, were undoubtedly kicked off of the giant asteroid from that impact, and some of them made it to Earth! But back to these three "snowman" craters -- Marcia, Calpurnia, and Minucia -- we've got a true-color image of their interiors as well, and they... well, it's simply remarkable.

Image credit:

Vesta itself is quite rare in many ways: it rotates very rapidly, completing a rotation in less than 6 hours, and it's inclined both to the ecliptic (at 7 degrees) and on its axis (at 29 degrees), so that there are no permanently shadowed craters. If we could watch Vesta from afar in space, this might be what we'd see.

Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA; wikimedia user Little Mountain 5.

And while that might strike you as absolutely amazing -- and well, it is -- it's still not the most spectacular thing I've got to show you. A huge German collaboration has put together this remarkable flyover sequence of Vesta, complete with explanations of what was discovered, and I can't do it any better justice than the team has already done. (Full info here.)

On the night of September 4th/5th, Dawn will depart Vesta for good to make its way to Ceres, the largest and most massive object in the entire asteroid belt, and will work its magic over there. This is as close as we've ever come to understanding the formation of the Solar System and -- by extension -- the ultimate origins of everything on our world.

esiegel Thu, 08/30/2012 - 11:59

There could be H2O ice on Vesta

gregladen — Wed, 25 Jan 2012 14:29:56 +0000

There could be H2O ice on Vesta

Vesta is the second biggest asteroid in the famous asteroid belt between Mars and Jupiter. It has generally been thought that Vesta would get enough sun over its entire surface that water would not survive, but a recent survey of the surface indicates that deeply buried water has a chance of remaining on the asteroid near the poles, or possibly at the bottom of some deep craters.

Vesta Up Close (image by NASA)

This is interesting, in part, because of questions about the role of water in the early formation of the solar system. One of the main objectives of the Dawn spacecraft mission is to examine water (or the lack of water) on Vesta and Ceres (another asteroid).

Dawn is looking for water using the gamma ray and neutron detector (GRaND) spectrometer, which can identify hydrogen-rich deposits that could be associated with water ice. The spacecraft recently entered a low orbit that is well suited to collecting gamma ray and neutron data.

"Our perceptions of Vesta have been transformed in a few months as the Dawn spacecraft has entered orbit and spiraled closer to its surface," says Lucy McFadden, a planetary scientist at NASA Goddard and a Dawn mission co-investigator. "More importantly, our new views of Vesta tell us about the early processes of solar system formation. If we can detect evidence for water beneath the surface, the next question will be is it very old or very young, and that would be exciting to ponder."

The modeling done by Stubbs and Wang, for example, relies on information about Vesta's shape. Before Dawn, the best source of that information was a set of images taken by NASA's Hubble Space Telescope in 1994 and 1996. But now, Dawn and its camera are getting a much closer view of Vesta.

"The Dawn mission gives researchers a rare opportunity to observe Vesta for an extended period of time, the equivalent of about one season on Vesta," says Stubbs. "Hopefully, we'll know in the next few months whether the GRaND spectrometer sees evidence for water ice in Vesta's regolith. This is an important and exciting time in planetary exploration."

NASA press release

gregladen Wed, 01/25/2012 - 09:29

Four First Glimpses

milhayser — Fri, 13 Jan 2012 09:25:24 +0000

Four First Glimpses

When the stars align, the results can be nothing short of spectacular. On Starts With a Bang, Ethan Siegel shows us an "Einstein ring" photographed by the Hubble Space Telescope. This celestial halo surrounds a massive red galaxy, and is in fact light from a much more distant galaxy focused by gravity. Ethan explains, "gravity will bend spacetime, forcing light into a curved path. If a very distant galaxy is properly lined-up with us and a less distant—but very massive—galaxy, its light will not only be bent into a ring if the alignment is perfect, but its light will be greatly magnified, making a dim galaxy appear very bright." The newly-imaged LRG 3-757 "makes about 80% of a full ring: a cosmic horseshoe." A never-before-seen galaxy is also visible on Greg Laden's Blog: GN-108036. Greg says this galaxy produces stars "at the rate of about 100 per year. In contract, the Mikly Way (our galaxy), even though it is 100 times bigger in mass than GN-108036, produces about 30 new stars per year." Amazingly, we are seeing this galaxy as it existed only 750 million years after the big bang. Greg also has the first low-altitude images of the massive asteroid Vesta, taken by NASA's Dawn spacecraft. And on Starts With a Bang, Ethan covers Kepler's discovery of the first exoplanet smaller than Earth, whose very hot year is shorter than a week.

A Holiday Hubble Handout: A Horseshoe? on Starts With a Bang!
Galaxy from distant past is very fertile on Greg Laden's Blog
Dawn Obtains First Low Altitude Images of Vesta on Greg Laden's Blog
First Exoplanet Smaller Than Earth: Why I'm Not Surprised on Starts With a Bang!

milhayser Fri, 01/13/2012 - 04:25