These Hubble Space Telescope images of Vesta and Ceres show two of the most massive asteroids in the asteroid belt, a region between Mars and Jupiter.
The images were used to help astronomers plan for the Dawn spacecraft’s tour of these hefty asteroids before it even launched.
representative of the final, bigger planetary embryos,
which came together to form the planets almost 4.6
billion years ago. Only a few of these now remain in
the inner solar system. Dawn is revealing the conditions under which these objects formed and the different ways in which they have evolved in this key
region close to where the so-called ‘frost-line’ may
have existed. This is the limit beyond which water was
able to condense into ice, due to lower temperatures
in the solar nebula, whereas in the hotter environments
closer to the early Sun water would have combined
with other substances to form hydrated minerals.
Ceres and Vesta have been altered much less than
other bodies. The Earth is very active and constantly
evolving, but Ceres and Vesta are ancient and have
preserved a record of the early solar system. Dawn’s mission’s goals include determining their composition and
internal structure. By examining their surfaces and how
they have been modified by impactors over time, we
can get an idea of what the early conditions of Ceres
and Vesta were like and how they have evolved since
years of total thrust time, giving it an effective change
in speed of 11 kilometers/second, or well over 24,000
miles/hour. That is about the same as the entire Delta
rocket with its 9 solid motor strap-ons, first stage, second stage, and third stage, and it is far in excess of
what any single-stage craft has accomplished.’
The target worlds:
Why Ceres and Vesta?
Launched by NASA on September 27, 2007, Dawn’s
targets for study are two of the most massive objects of
the asteroid belt. While small compared to Earth, dwarf
planet Ceres (formerly asteroid 1 Ceres) contains roughly
30% of the total mass in that region of space and protoplanet Vesta (fromerly asteroid 4 Vesta) 8%, so Dawn
is exploring almost 40% of the asteroid belt’s mass. For
other statistics on these worlds, see Table 1 below.
Both bodies are regarded as protoplanets,
Table 1: Ceres and Vesta at a glance, compared to Earth and our Moon
Mean diameter
(km)
Mean distance
from Sun (AU)
Mean distance
from Sun (million km)
Orbital period
(years)
Vesta
525
2.36
353
3.63
2.59 x 1020 3.456
Ceres
952
2.77
414
4.60
9.43 x 1020 2.077
Earth
12742
1
150
1
5.97 x 1024 5.51
Moon
3474
-
-
-
7.35 x 1022 3.346
28
28
Mass
(kg)
Mean density
(g/cm3)
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