Sedna mystery deepens as Hubble offers best look at farthest planetoid

At a distance of over 8 billion miles (13 billion kilometres), Sedna is so far away it is reduced to one picture element (pixel) in this image taken in high-resolution mode with Hubble's Advanced Camera for Surveys. This image sets an upper limit on Sedna's size of 1,000 miles in diameter. Hubble may just barely be resolving the object. It is surprising that Hubble does not see a suspected moon near the planetoid. Either the moon's not there, or, far less likely, it is being eclipsed by Sedna, or it is transiting Sedna. The gravitational tug of a moon would best explain Sedna's extremely slow rotation of 40 days as inferred from ground-based photometric observations.