Visible and near-infrared (VNIR) reflectance spectroscopy provides a powerful means
of remotely characterizing the mineralogy, mineral chemistry and mineral abundance
on the surface of a planetary object or a region of the earth. For the foreseeable
future, remote sensing studies will provide the only characterization of most small
solar system bodies. These small planetary objects preserve the best record of the
earliest history of the Solar System. In a very real sense they are "Rosetta Stones."
My research in this area is concentrated in (a) developing and improving the interpretive
techniques for the analysis of VNIR spectra of geological materials, especially
the meteorites, (b) characterizing the mineralogical and petrologic properties of
asteroid surface materials from telescopic spectral observations and (c) investigating
the implications of these asteroidal data for the early evolution of the inner solar
system and the terrestrial planets, for the source of the meteorites and for possible
utilization of extraterrestrial resources.
The asteroids represent the residue of the population of planetesimals which accreted
to form Earth, Mars and the other terrestrial planets. Because of their small size
and location, the asteroids preserve a record of the conditions which were present
and the processes which were active prior to and during this accretionary epoch.
Determination of these conditions and processes helps to better understand the relationships,
nature and history of the inner planets.
Detailed investigation of selected asteroids indicates a diverse evolutionary history
for objects in this population. Rotational studies have been used to map out the
gross variations of lithology across the surfaces of several asteroids. In one such
case, the materials present on the surface of the asteroid (4) Vesta indicate that
this body was intensely heated and underwent large-scale magmatic differentiation.
The type and variety of assemblages on Vesta indicate that this minor planet is
still intact. By contrast, most inner belt asteroids have been broken up by collisions
to expose their metal-rich core regions. Few objects of the outer belt have undergone
even moderate heating and fewer are broken up.
The small size (1000 km) and the radial dependence of thermal history suggest that
the inner solar system experienced a brief, intense heating episode about 4.55 +/-
0.05 billion years ago. Soon after, the inner asteroid belt and the region of proto-Mars
was subject to an intense bombardment episode, which smashed most of the planetesimals
in this portion of the solar system, and apparently aborted the growth of Mars.
This bombardment was probably triggered by the growth of Jupiter above some critical
Asteroid studies indicate that the bodies which accreted to form the Earth had been
strongly heated and differentiated prior to incorporation into the planet. This
points to the very early appearance of the terrestrial ocean and atmosphere, a result
consistent with the increasing age of fossil evidence for life on Earth.
The asteroid studies thus provide constraints on the chronologies of planetary growth,
and on the type of material available for incorporation into each of the terrestrial
planets. These conditions then set the stage for the subsequent geologic evolution
of the Earth, Mars, Venus, Mercury and the Moon.