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Re: Vesta questions
Jim Hurley writes:
>I have several questions about Vesta, possibly the source for
>eucrites.
>
>Vesta is about 525 kilometers wide and yet it is claimed to be
>differentiated.
>Except for the large impact crater, it's surface is considered to
>be about the same as it was in the early days of the solar system.
Actually, its surface would be expected to be filled with thousands
of impact craters. The best images we have of the asteroid were
taken by the Hubble Space Telescope in Earth orbit, which can only just
barely make out a couple of large craters.
>So, in the earliest days of the solar system we have a minor planet
>that had a molten core, some volcanic activity and which later cooled
>down and remained in that form up till now.
That is true, except you can still expect to have collisions between bodies
after the "Big Bombardment" period, but at a lower frequency.
The consensus is that most of the collisions, but not all, occurred
early on in the formation of the solar system. However, that does not mean
that additional impacts did not occur later on.
>a) how small can an object be and still undergo differentiation?
About 175 km in diameter. Vesta is much larger than that. The lava
flows on Vesta happened early on before its
interior cooled off.
>b) I though most asteroids came from collisions between larger objects
> and that very few are still in their original composition.
The "larger objects" you are referring to are the larger asteroids, and
Vesta is in fact one of the larger objects in the asteroid belt.
Were you expecting all asteroids to be exactly the same size? They
come in various sizes, shapes and compositions.
Also, collisions don't change the gross composition of an asteroid.
Most scientist think that asteroids formed in the asteroids of various
sizes, and over the eons have continued to collided with each other.
>If this
> is correct, why is Vesta so fortunate to have missed the breakup and
> rebuilding process that most other bodies underwent?
Which other bodies have been broken up and rebuilt?
Please provide specific examples.
Being a larger body helps Vesta survive collisions, and there is no
doubt it has collided many times with other asteroids over the billions
of years. There are 20 smaller asteroids associated with
Vesta since they have matching spectra and orbit characterstics, and
they all may not have necessarily been broken off of Vesta from the same
collision.
Our closeup looks of all of the asteroids we've observed (Gaspra, Ida,
Mathilde & Toutatis) show them to be bodies pittmarked with many craters
of various sizes. There is no reason to believe that Vesta is similarly
cratered.
Ron Baalke
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