Wikipedia:
List of exceptional asteroids: Largest by diameter).
Vesta facts:
-
Astronomical symbol:
⚶.
- Mean orbital radius:
2.36179 AU.
- Eccentricity: 0.08874.
- Orbital period: 1325.75 days
= 3.62971 Julian year.
- Sidereal rotation period: 0.2226 days = 5.342 hours
prograde (i.e.,
eastward as seen on the
sky and rightward in the
film version of this image:
see
file
004_vesta_rotating.html).
The rotation axis is the short axis??? and it is tilted by 29° from the
ecliptic axis.
- Mean radius: 262.7 ± 0.1 km.
- Dimensions: 572.6 x 557.2 x 446.4 km. It is NOT very round as you can see.
Self-gravity
has NOT won a complete victory in spherizing
Vesta over the
centrifugal force
and the rigid chemical bonds
of solids.
- Oblateness f = (a-b)/a = 0.2204,
where a is equatorial radius and b is polar radius.
- Mass:
2.59076(1)*10**20 kg
= 4.33791*10**(-5) Earth masses
= 3.529*10**(-3) Moon masses
= 0.2758 Ceres masses.
The north polar region is roughly at the top and the south polar region is roughly at the bottom.
The film version of this image
(see file
004_vesta_rotating.html)
changes orientation as
is goes along, but the north polar region is roughy at the top and the south polar region is roughly at the bottom
is still true.
Vesta is often considered a true
protoplanet left over from
Solar System formation
since it had
chemical differentiation
by
primordial-radiogenic heat geology
(see also Wikipedia:
Earth's internal heat budget: Radiogenic heat: Primordial heat)
in its early days.
The primordial-radiogenic heat geology
turned off of order
10 Myr after formation
(Wikipedia: 4 Vesta: Geology).
The turn-off was due to the exhaustion of
its initial formation heat energy
and probably
aluminum-26 (half-life 0.717 Myr)
which was probably a main source of
heat energy
(see
Wikipedia: Aluminium-26: Occurrence in the interstellar medium;
Wikipedia: 4 Vesta: Geology).
Vesta is sufficiently small that
it loses heat energy too quickly
from the radioactive decay
of long-lived radioactive isotopes
(e.g., uranium-238 (half-life 4.468 Gyr))
for those radioactive isotopes
to power
primordial-radiogenic heat geology.
See radiogenic_heat.html for
long-lived radioactive isotopes.
The relatively short-lived radioactive isotopes
(like aluminum-26)
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.
The
primordial-radiogenic heat geology
powered volcanism
on Vesta and this gave
Vesta some
basaltic rock.
Perhaps many asteroids
larger than 100 km underwent some
chemical differentiation
and
volcanism in their first few million years
due to heat energy from formation
and relatively short-lived radioactive isotopes.
Vesta like most
airless rocky-bodies.
has many impact craters
mostly probably left from the
heavy bombardment
in the early Solar System
(4.6--3.8 Gyr ago).
Since then meteoritic weathering
and
diurnal temperature cycle weathering
have ground the surface down to mostly
regolith which gives the surface
a soft powdery look which is also typical of
airless rocky-bodies.
A prominent feature of Vesta
is Crater Rheasilvia
that is roughly centered on the south pole.
It is NOT clearly shown in the
film version of this image
(see file
004_vesta_rotating.html).
Crater Rheasilvia has
a diameter of 525 km and
a central peak rising 22 km
about the base---which makes it the highest
mountain
in the Solar System by some standard
(see Wikipedia:
List of tallest mountains in the Solar System).