Some Consequences of Planetary Migration on the Primordial Asteroids

R.S. Gomes (Observatório Nacional - Brazil)

Just after the dissipation of the Solar Nebula, a global outer Solar System planetary migration may have taken place (Fernandez & Ip, 1996, Planet. Space Sci, 44, 431). This phenomenon may have determined important consequences on the dynamics of the primordial Solar System, including the placement of Pluto and possibly the Edgworth-Kuiper belt objects in their present orbital configurations (Malhotra 1995, Astron. J., 110, 420) and the depletion of asteroids from the outer main belt (Liou & Malhotra 1997, Science, 275, 375). Here, I investigate the consequences of migration on the primordial asteroids of the inner main belt as well as the primordial Trojan asteroids and Trojan-type asteroids for the three outermost major planets.

The main result of Jupiter and Saturn migration on the primordial inner belt (2.1 to 3.2 AU) asteroids is determined by the sweeping of the secular resonance tex2html_wrap_inline16 through all range of considered semimajor axes. The place of the secular resonance tex2html_wrap_inline18 also changes to near 2.7 AU for the initial planetary positions just before migration. This process would have excited the eccentricities and inclinations of most primordial asteroids, yielding a possible catastrophic scenario, which may have prevented the formation of a planet in the asteroidal region. Today's main belt asteroids may be the final product of this process, by which most primordial asteroidal mass may have been lost and the asteroids eccentricities damped to more modest values.

If there were asteroids trapped in 1:1 resonances with the major planets before migration, this phenomenon would be responsible to the depletion of much of Jupiter Trojan asteroids mass. This process would have been much more effective for Saturnian Trojans, for which asteroids are released from resonance before 1/10 of the total migration time has elapsed. For Uranus and Neptune, however, migration showed an even more stable character for their "Trojans", as compared to Jupiter Trojans. Thus migration can give an explanation for why no Saturnian Trojan-type asteroid has been found up to date, but another explanation is still in order for why there would be no "Trojans" for Uranus and Neptune.