Caption: Asteroid Vesta in a direct image (from the HST, 1997), a model, and a topographic map.
Vesta (formally 4 Vesta), the 3rd largest asteroid, has average diameter 525.4 km. But despite its large size, it isn't all that spherical as one can see. Self-gravity has NOT won a complete victory in spherizing Vesta
A large impact crater with a crater central peak near the south is clear on the topographic map. The impact crater has a diameter of about 400 km.
Vesta has basaltic rock, and so is thought to have undergone volcanism and chemical differentiation in the early Solar System.
Perhaps many asteroids larger than 100 km underwent some chemical differentiation and volcanism in the early Solar System.
But their residual heat of formation and past radioactive heat were lost quickly and they became inactive for internal-heat geology early on.
Vesta and smaller
asteroids
might have owed their
heat energy and
chemical differentiation
and internal heat due to
aluminum-26 (half-life 0.717 Myr) and
perhaps other
relatively short-lived radioactive isotopes
(see
Wikipedia: Aluminium-26: Occurrence in the interstellar medium;
).
The short-lived radioactive isotopes
would have to have been produced by a supernova
that went off shortly before Solar System formation
and that seeded the
primordial nebula
with its debris enriched in metallicity
and radioactive isotopes.
See reference see Se-565.
Credit/Permission: NASA,
1997 /
Public domain.
Image link: itself.
Download site: Views of the Solar System by Calvin J. Hamilton.
File: Asteroid file:
004_vesta_hst.html.