No moon for Sedna?

“In the weeks following the discovery, researchers expected Hubble to reveal images of a moon revolving around the newly found planetoid named Sedna. This is because Sedna appears to have a very slow rotation, which usually would mean the planetoid is slowed by the gravitational pull of a body revolving around it.

So far, any indication of a companion moon of any substantial size hasn't been seen.

"I'm completely baffled at the absence of a moon," said Mike Brown of the California Institute of Technology. "This is outside the realm of expectation and makes Sedna even more interesting. But I simply don't know what it means."

Sedna's rotation has been calculated to take 40 days compared to Pluto's six-day period. If in time this proves to be accurate, Sedna would be the slowest rotating object in the Solar System after Mercury and Venus.

NASA's Hubble Telescope, using its new Advanced Camera for Surveys, only showed Sedna in its observations. But there is still a small possibility that the planetoid has a moon that could be behind Sedna or in front of it.

In both cases, Hubble would not be able to see it. According to Brown, doing so would be like trying to see a soccer ball that is 900 miles away.”