New Scientist: Vesta is the second most massive and third largest asteroid in the main belt and is classed as a minor planet. Like Ceres and Pallas, the other two most massive and largest asteroids, it doesn't have any natural satellites. That the three largest asteroids don't have any moons is curious because more than 100 main-belt asteroids are known to have other bodies in orbit around them. Vesta in particular looks like it ought to have a moon because its surface shows two large craters whose formation by impact should have created enough debris to form satellites. Lucy McFadden of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and her colleagues examined flyby images from the Dawn spacecraft to confirm the absence of any bodies larger than 6 m orbiting Vesta. Nick Gorkavyi, also of NASA Goddard, suggests that Vesta's high rate of rotation could have resulted in any satellites that formed losing momentum and merging with the asteroid. Gorkavyi says such merging events could explain the large canyons on Vesta's surface.
