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.