NASA Probe to Uncover Secrets of Brightest Asteroid Vesta ('Dawn' probe to orbit protoplanet)

SPACE.com ^ | 7/15/11 | Charles Q. Choi

[NormsRevenge]

The asteroid Vesta may be the brightest asteroid in the solar system, but it remains shrouded in mystery.

When NASA's Dawn probe enters into orbit around Vesta on July 15 — the first spacecraft to visit the 330-mile-wide (530-kilometer) protoplanet — it promises to shed light on the many enigmas of the second-largest body in the asteroid belt.

NASA launched the $466 million Dawn mission in 2007, with Vesta as the first (but not last) stop. The Dawn probe is also expected to visit Ceres, the largest asteroid in the solar system, but only after unlocking the secrets of Vesta. Here's a look at the main questions astronomers hope the probe will help solve:

Why is Vesta so bright?

Vesta is the brightest asteroid, with a surface about three times as bright as Earth's moon, "and why it is so bright is the No. 1 mystery of Vesta," planetary scientist Christopher Russell, principal investigator for NASA's Dawn spacecraft, told SPACE.com. ..

When one looks at the most reflective celestial bodies in our solar system, Venus is the most reflective planet because of its clouds, and the sixth-largest Saturn moon Enceladus is the most reflective body overall because of its snow, "but Vesta doesn't have an atmosphere or snow," Russell noted. "Hopefully when Dawn inspects Vesta's surface, we'll get an answer."

[SunkenCiv]

Thanks NormsRevenge.

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[dr_lew]

Well, they released this amazing picture:

... but no commentary. I say amazing because those ridges are very reminiscent of Enceladus, e.g. which is ice, and they have been firm in saying that Vesta is dry. Also, that big lump lower left is quite interesting. ( Note light is from the right. ) Well, I guess we'll hear plenty about it if we wait a little.

[17th Miss Regt]

That lump is probably an accreted mass that impacted with enough force to stick to the rest of Vesta but not to shatter the accreted mass into bits. The weak gravity would not have been enough to cause the complete absorption of the mass, so there it sits today. On display sort of as a warning to other asteroids. (Warning of what? I don’t know!)

[dr_lew]

That lump is probably an accreted mass that impacted with enough force to stick to the rest of Vesta but not to shatter the accreted mass into bits.

It certainly gives that impression, almost as if it was a blob of clay, but I'm not sure how that fits in with the physical models that they have for this sort of process. I wonder how much of puzzle this image presents. They always brag about how they love surprises, but maybe they didn't really expect a surprise here, or maybe they'll just say this is what they expected anyway.

According to this article, it accreted and "evolved" before being bombarded. I don't see anything accounting for an accreted lump. They show a model, pre-encounter of course, that shows a bump at the bottom. I think this is supposed to be the wall of the crater at the south pole that they talk about. I have trouble lining all these things up. For instance, it's oblate, so isn't the south pole on one of the flat sides? The new picture must have the poles to the right and left ... right ? You have to dig for this stuff.

[17th Miss Regt]

I am not sure just how much it could ‘evolve’ if it is that small. Any internal forces (causing melting) and the weak gravitational field are not enough to form it into a fairly smooth ball. Mystery to me....

[dr_lew]

The "blob" in the July 9 image I posted is evidently the central peak of the huge impact crater near the south pole, so it is a result of plastic deformation during the impact event, even if it's not simply a glob of material that stuck to the asteroid.

The Dawn Gallery now has several additional images showing this feature. Since it's near a pole, it should remain in view as the craft approaches from a distance. However, you can see the shift in the line of the terminator as the craft starts to move into orbit.

I loved Eros ;-) and I'm loving Vesta too!