Techniques d'observation spectroscopique d'astéroïdes

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Why asteroids?
tel-00785991, version 1 - 7 Feb 2013
Even if the total mass of the asteroids is insignificant in rapport with the total mass of the planets, their
large number, wide distribution throughout the Solar System and extremely divers composition makes them
a valuable resource for Solar System studies. This introductory chapter provides a general overview of this
population. The asteroids place in the diversity of the Solar System objects is described based on the scientific
literature. Some briefly notes about asteroids discovery, following an historical line are given. The main
physical properties of these objects are outlined. At the end of the chapter is made a short summary regarding
my contribution in the discovery of the asteroids are outlined.
1.1 The place of asteroids in the structure of the Solar System
Asteroids are well-preserved samples from the first phase of the Solar System formation which
started 4.57·10 9 years ago. In order to discuss their physical properties it is useful to trace
back the events that took place at the beginning of the Solar System. According to the Solar
Nebula Disk Model, the Solar System emerged from a large molecular gas and dust cloud
which accumulated sufficient mass and density for gravitational collapse to occur. When the
gravitational collapse was triggered (typically by random turbulence which locally increase the
density within the cloud), the gas and dust cloud condensed until it formed a central mass and
a protoplanetary disk that surrounded it.
As a consequence of the angular momentum conservation, the rate of rotation of the disk
and central mass increased as it collapsed. The central mass continued to grow until it formed
a protosun. When enough mass was accumulated for fusion to occur it became the Sun. At this
stage a strong temperature gradient across the disk was present. The gradient of the temperature
into the protoplanetary disk determines the distance where the different components started to
condense. The inner disk was too hot for the condensation of volatiles, so it was dominated
by rocky material, while the outer disk had a mixture of volatiles and ices. Within the disk,
micron-size dust grains collided at velocities forming bodies up to a kilometer in size. Many of
these large bodies collided and merged or ejected other bodies and eventually grew to planetary
sizes [DeMeo, 2010].
This part of the planetary formation process occurred over a period of less than 10 millions