DOI: 10.1029/2004je002343
View full text

Abstract: It is shown in this paper that five giant impact basins of Mars, Argyre, Hellas, Isidis, Thaumasia, and Utopia, are located on a single great circle. This suggests that the projectiles' orbital planes coincided with the equator of Mars at the time of impact. The projectiles were larger fragments of a heliocentric asteroid that broke apart as it entered the Roche limit of Mars. The mass of the asteroid was at least ∼9.8 × 1020 kg, ∼1.5 × 10−3 times the mass of Mars.