Wednesday, October 08, 2008

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.


cda said...

Are you saying there is an object the size of Mars two light years from the sun, i.e. half way to Alpha Centauri? Do astronomers consider such an object to be part of the solar system? Stretching it more than a bit!

KRandle said...

I am looking at Discover magazine for November 2004. They reported on objects beyond Pluto, the farest out they name is Senda at 486 AU... but they also report on "Planet X" about the size of Mars and "Planet Y" that they suggest is halfway to Alpha Centauri... but neither of which they have good astronomical data for.

They report on seven objects beyond Pluto that range in size from about 500 miles in diameter to about 1000 miles, which makes them all smaller than Pluto.

So yes, they are talking about objects halfway to the next star that are still part of the Solar System. If I remember correctly, astronomers have postulated a second Oort Cloud about about that far.

So, we are still at eight planets, five dwarf planets, but with a possibility of adding a ninth planet and about another dozen dwarf planets.

JRobinson said...

As CDA suggested, considering a Mars-size object 2 light years away to be part of the solar system is pretty wild. Such an object would have an orbital period of about 46 million years, & since the sun's gravitational hold is so weak out there, it could be easily ejected from the system by even a far encounter with another body of similar size.

Anyway, a planet at that distance would have to be at least 20x larger than Mars to even be detected by the largest telescope on Earth, much less have its size determined!

KRandle said...

All I can tell you is that what Discover said in November 2004. Yes, I realize that something that far away would be difficult to detect and that the Sun's gravitational hold would be weak... and I am surprised that the Alpha Centuri system hasn't grabbed it by now, but we are seeing things far beyond Pluto and some of them are extremely small. They've even seen the moons around a couple of these objects that are quite tiny.

So, yes, as long as the object is in orbit about the sun, it's part of the solar system. I'm waiting to see these things updated which is why I look for articles about them occasionally.