The Search for Moons for Asteriod 4 Vesta

Only eight more days and counting until Dawn reaches the acclaimed asteroid 4 Vesta! But, let's pause from this excitement and consider the fact that Vesta may house moons. You might ask, 'How can an asteroid have moons?' or 'It's too small to have any gravitational pull strong enough to capture anything.' Well, you are sadly mistaken. We don't know if asteroid 4 Vesta has moons, but an asteroid having moons is quite common: take asteroid Ida and it's moon Dactyl for example (pictured below).

Taken by the Galileo spacecraft in 1994, it's true that asteroids can have moons.

But, that's only one asteroid. Surely other asteroids have moons, don't they? Yes, that's true. In 2000, asteroid 762 Pulcova was found to have a moon. In 1978, asteroid 532 Herculina was found to have a moon. These asteroids which have moons are called 'binaries' and an asteroid with three moons is called a 'triple.' 

Some triple systems include: asteroid 87 Sylvia with Romulus and Remus (below Pulcova) and 3749 Balam (March 2008). There is at least 100 more which do, so it is quite possible that asteroid 4 Vesta houses a moon or two.

762 Pulcova and it's moon.

87 Sylvia with Romulus and Remus.

"For starters," says Dawn chief engineer Marc Rayman, "we're going to look for an asteroid moon." Tomorrow, on the ninth of July, moon-searches will start their search to find Vesta-moons while Dawn is approaching the sullen object. "If a moon is there, it will appear as a dot that moves around Vesta in successive images as opposed to remaining fixed, like background stars," says Dawn Co-investigator Mark Sykes, who is also director of the Planetary Science Institute. "We'll be able to use short exposures to detect moons as small as 27 meters in diameter. If our longer exposures aren't washed out by the glare of nearby Vesta, we'll be able to detect moons only a few meters in diameter."

So, as we wait excitedly for Dawn and Vesta to unite, Raymond had an idea for a moon if they found one, commenting "How about Dawn?"