Techniques d'observation spectroscopique d'astéroïdes
Techniques d'observation spectroscopique d'astéroïdes
Techniques d'observation spectroscopique d'astéroïdes
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36 CHAPTER 1. WHY ASTEROIDS?<br />
4:1<br />
3:1 5:2 2:1<br />
4:1<br />
3:1 5:2 2:1<br />
tel-00785991, version 1 - 7 Feb 2013<br />
(a)<br />
Figure 1.2: a) The position of asteroids in the inner part of the Solar System (Source: http://en.<br />
wikipedia.org/). b)The distribution of asteroids in a representation (a,e)- bottom and (a,sini) - top, a is<br />
the semi-major axis and i the inclination [Nedelcu, 2010].<br />
located in the Main Belt, at heliocentric distances between 2.1 and 3.3 AU 3 (these are called<br />
Main Belt Asteroids - MBAs). Several gaps and concentrations can be distinguished by plotting<br />
the distribution versus semi-major axis (Fig. 1.2b). These gaps are called Kirkwood gaps<br />
and correspond to the locations of resonances with Jupiter (in the Fig. 1.2 there are marked<br />
4:1, 3:1, 5:2, 2:1 resonances). The 3:1 and 5:2 resonances located at 2.5 and 2.82 AU, respectively<br />
define the boundaries between the inner (2.0 - 2.5 AU), middle (2.5 - 2.82 AU), and outer<br />
(2.82-3.3 AU) regions of asteroid belt.<br />
(b)<br />
The MBAs have diameters up to ≈500 km (Pallas, Vesta). Ceres, the largest body from the<br />
Main Belt, which has a diameter of ≈1000 km is classified as a dwarf planet.<br />
Inside the Main Belt, several clusters of asteroids could be identified [Birlan & Nedelcu,<br />
2010]. These are called asteroid families and are defined by Zappala et al. [1995] as a group<br />
of bodies that are genetically and dynamically linked as a result of a catastrophic event: collision<br />
of two bodies followed by the destruction of both target and impactor. Usually, they are<br />
identified as groups in the space of orbital proper elements [Milani & Knezevic, 1990]..<br />
According to Minor Planet Center (as of August 2012), a total of 5,188 asteroids were<br />
discovered near Jupiter’s Lagrangian points L 4 (3404 objects) and L 5 (1784 objects) - Fig. 1.2a.<br />
These objects are called Trojan asteroids. They are characterized by low albedo. The largest<br />
body is (624) Hektor with a mean radius ≈100km [de Pater & Lissauer, 2010]. Several Mars<br />
and Neptune Trojans have also been discovered.<br />
3 AU is an astronomical unit of distances, 1AU = 149,597,870,700 m (≈ the average Earth - Sun distance.)
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