BALTIMORE -- Pictures of the newly discovered planetoid Sedna show it moonless, spinning alone some 8 billion miles from Earth.
Sedna, though, still might have a moon that was hiding somewhere or too dark to be photographed by the Hubble Space Telescope, said astronomer Mike Brown, its discoverer.
Given the planetoid's slow rotation, the seeming lack of a moon surprises Brown.
"I still am convinced there is one there, and it's just darker than we expected and we haven't seen it yet," Brown, of the California Institute of Technology, said Wednesday.
At 800 to 1,000 miles in diameter, Sedna is too small to qualify as a planet. It is only about three quarters the size of Pluto, its closest neighbor.
Objects that size should complete one rotation in a matter of hours, but observations so far show it takes 20 to 40 days, possibly due to the drag of a moon, Brown said.
The Hubble Space Telescope took 35 visible light images in March, after Brown announced the discovery of the frozen, crimson world - the most distant object in our solar system.
The images show Sedna with a faint, distant star in the background. There is a small chance a moon could have been behind or in front of - and indistinguishable from - the planetoid, Brown said.
While the first set of images concentrated on blue light to more accurately determine Sedna's size, that also raised the possibility of overlooking a faintly lit moon. Brown said he is hoping to use the Hubble again and concentrate more on the red end of the visible light spectrum in hopes of detecting a companion.
If there is a moon, Brown said he expects it should be about 400 miles across. Other possibilities include the destruction or the loss of the moon after it slowed Sedna's rotation, he said.
The pictures were released by the Baltimore-based Space Telescope Science Institute, which operates the Hubble.
The planetoid, believed to be half rock and half ice, is named after the Inuit goddess said to have created the sea creatures of the Arctic.
On the Net:
Hubble Sedna pictures: http://hubblesite.org/news/2004/14