Institute of Astronomy

Stop hitting yourself: did most terrestrial impactors originate from the terrestrial planets?

SpeakerTalk DateTalk Series
Alan Jackson28 July 2014Across HR 2014 Posters


Although the asteroid belt is the main source of impactors in the inner solar system today, it contains only 0.0006 Earth mass, or 0.05 Lunar mass. While the asteroid belt would have been much more massive when it formed, it is unlikely to have had greater than 0.5 Lunar mass since the formation of Jupiter and the dissipation of the solar nebula. By comparison, giant impacts onto the terrestrial planets typically release debris equal to several per cent of the planet’s mass. The Moon-forming impact on Earth and the dichotomy forming impact on Mars, to consider but two of these major events, each released >1 Lunar mass in debris, over 50 times the present day asteroid belt. This escaping impact debris is less long lived than the main asteroid belt, as it is injected on unstable, planet-crossing orbits, but this same factor also increases the impact probability with the terrestrial planets and asteroids. We show that as a result terrestrial ejecta played a major role in the impact history of the early inner solar system, and we expect the same is also likely to be true in other planetary systems.