Wednesday, October 08, 2008

A New Dwarf Planet

This one I missed. I was scanning the Internet the other day and for fun, I thought I would see if some of those sites that still talk of nine planets in the Solar System had been updated (No, they haven’t), when I discovered that the number of dwarf planets had increased by one. It seems that the object, once called Santa, was now named Haumea and was the latest of the Kuiper Belt Objects (aka Plutoids) to reach dwarf planet status.

This is a strange one for a couple of reasons. First, Mike Brown and his Caltech team said that they had discovered it in December 2004 while looking at images taken on May 6, 2004. They published an online abstract on July 20, 2005 and were going to announce the discovery at a conference in September. Before this got much farther, Jose Luis Ortiz and his team at the Instituto de Andalucia in Spain said that he had found the object on pictures they had taken in March 2003.

Brown learned that Ortiz had accessed his, Brown’s, observation logs, and Brown thought that Ortiz had done that so that he could backtrack to his own images. Ortiz denied that, but did admit he had accessed the logs, simply to be sure that they weren’t observing an object already cataloged.

I don’t know who is right here, but I do know that in the end, Brown’s team named the new object for the Hawaiian goddess Haumea. On September 17, 2008, the IAU said that this name had been accepted. This would seem to be proof that the IAU had accepted Brown and his team as the discoverers.

The second strange thing is that Haumea is elongated. It is not spherical, which means that it falls outside one of the criterion for a dwarf planet. They are supposed to be able to reach equilibrium, or, in other words, have a gravitational field strong enough to pull it into a relatively spherical shape. Since it rotates on its axis about once every four hours, it’s spinning faster than any other known equilibrium body in the Solar System, so this might account for its strange shape and allows it to slide past this idea that dwarf planets must be relatively spherical.

This is not to mention the size. It’s about 1150 km in diameter or about half the size of Pluto and Eris, a little smaller than Makemake and about twice the size of Ceres.

Like two of the other Plutoids, Haumea has a couple of moons, named Hiiaka and Namaka. Hiiaka was discovered first and is thought to be about 310 km in diameter. Namaka is smaller, closer to the planet, and was discovered not long ago.

There are quite a number of other objects that are being considered for dwarf planet status, including one in the asteroid belt, Vesta, which would join Ceres as the only dwarf planets between Mars and Jupiter. And there are discussions that one of the Trans Neptune Objects, something like two light years from Earth, is the size of Mars. Once the observational data are complete, it will be interesting to see how the IAU handles that. Will we get another class of planet that accounts for those at the edge of the Solar System, out beyond Neptune?

They’re still trying to decide if Charon meets the criterion for dwarf planet. Charon might not be orbiting Pluto, but the two of them orbit a central point not unlike a double star, and if true, then Charon would fit the definition of dwarf planet and its status would upgraded.

As I say, there has been quite a bit of change to the Solar System in the last few years. Planets demoted, dwarf planets defined, and the possibility of a Mars-sized object halfway to the next star, which might make an interesting way station if we get to the point of launching interstellar flights and it’s on the right side of its orbit... a bit of science fiction to brighten our day.

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