So as well as welcoming Ceres into the new dwarf planet club with Pluto we also have to say hello to 2003 UB313, colloquially known as Xena. Xena is in fact one of the reasons that the dwarf planet category was even created since its discovery was announced in 2005 and sparked quite a storm. It is fractionally larger than Pluto and this threw into question the willingness to call Pluto a planet but not Xena. We if you read back on the blog you’ll see what’s happened since but for now lets see what else we know about one of newest Solar System members.
A team of astronomers led by Mike Brown working in California discovered Xena along with several other objects shown in the image above (Quaoar, Sedna, 2005 FY9 and 2003 EL61) whilst searching for large outer solar system objects. They used a computer to analyse data taken of the stars which could detect objects that had moved. Originally they had been careful to look for objects that were moving quite quickly and Xena was missed entirely. But after discovering Sedna, which moved slower than anticipated, they went back and did a more detailed search only to find Xena there amongst the stationary stars.
The movie above shows three frames that illustrate nicely the movement that objects like Xena make across the sky giving themselves away at more than just stars. The three frames above were taken over the course of three hours. Can you spot Xena moving along in the top left quadrant of the image?
Xena is something like 2500 km across and orbits the Sun in a highly eccentric (tilted) 557 year orbit as shown in the related diagram. It is currently at its most distant point from the Sun and so is currently around 96 times further from us than the Sun is. Xena was later discovered to have its own Moon, currently nicknamed Gabrielle. Gabrielle is much smaller than Xena as far anyone can tell. The two are shown together in this optical image taken using the Keck Telescope in Hawaii.
Xena leads a group of large, outer solar system objects occupying the Kuiper belt in the far reaches of the Solar System. They are shown in the graphic at the start of this blog post and will no doubt be studied by many people in the coming decades. Some of them maybe yet join the ranks of the other dwarf planets if they are found to be spherical in shape.
As our ground-based telescopes become bigger, better and much more accurate in the coming ten to fifteen years, we may even get some amazing pictures of these bodies that lie so far away from the Earth.
