DesertFox
04-14-2004, 04:32 PM
When astronomers announced the discovery last month of Sedna, the most distant known object in the solar system, they were nearly certain it had an unseen satellite. New observations by the Hubble Space Telescope find no moon, however, deepening the mystery surrounding this already strange object.
Sedna is about three-fourths the size of Pluto. It is so far away that it takes 10,000 years to orbit the Sun. Its discovery has astronomers arguing over whether to call it a planet or a planetoid, and whether to count it as one of many objects in the Kuiper Belt, where Pluto roams, or the first known example of an expected halo of more distant objects called the Oort Cloud.
Caltech astronomer Mike Brown, who led the discovery, said Sedna's slow rotation rate had him convinced there was an unseen satellite exerting a gravitational tug.
Here's why: Most objects in the solar system that don't have companions complete a rotation, or day, in a matter of hours. There are many examples of fast-spinning asteroids and similarly whirling large, round Kuiper Belt objects. Pluto, on the other hand, has had its rotational period slowed to six Earth-days by its companion, Charon.
Sedna spins on its axis once every 20 Earth-days, or perhaps even more slowly, making the presence of a moon practically inevitable, Brown had thought. So shortly after the discovery, Hubble was pointed at Sedna.
"Much to our surprise, there's no satellite," he told reporters today.
More (http://msnbc.msn.com/id/4740224/)
Sedna is about three-fourths the size of Pluto. It is so far away that it takes 10,000 years to orbit the Sun. Its discovery has astronomers arguing over whether to call it a planet or a planetoid, and whether to count it as one of many objects in the Kuiper Belt, where Pluto roams, or the first known example of an expected halo of more distant objects called the Oort Cloud.
Caltech astronomer Mike Brown, who led the discovery, said Sedna's slow rotation rate had him convinced there was an unseen satellite exerting a gravitational tug.
Here's why: Most objects in the solar system that don't have companions complete a rotation, or day, in a matter of hours. There are many examples of fast-spinning asteroids and similarly whirling large, round Kuiper Belt objects. Pluto, on the other hand, has had its rotational period slowed to six Earth-days by its companion, Charon.
Sedna spins on its axis once every 20 Earth-days, or perhaps even more slowly, making the presence of a moon practically inevitable, Brown had thought. So shortly after the discovery, Hubble was pointed at Sedna.
"Much to our surprise, there's no satellite," he told reporters today.
More (http://msnbc.msn.com/id/4740224/)