New planet's new moon
Close on the heels of the discovery of the solar system's tenth planet -- that's what it is, live with it, ongoing controversies notwithstanding -- its discoverers, Mike Brown and co., have now found that it has a moon of its own.
Brown has given the planet the temporary nickname of Xena, after the TV show, and the moon Gabrielle, apparently after Xena's friend or sidekick. A real, permanent name must await:
a) the tenth planet's acceptance as a planet, instead of just another Kuiper Belt Object, by the International Astronomical Union,
b) acceptance of the name itself, which should be no problem, since Brown understands the rules (has to be a name from classical mythology, etc.) and thinks he has a good one.
The discovery was made possible by the Keck II telescope's Laser Guide Star adaptive optics (LGS-AO) system to provide ground-based resolution in the infrared comparable to Hubble's in the visible.
Xena itself, at an estimated 2700 km diameter (larger than Pluto), is the most distant object ever detected in the solar system -- 97 Astronomical Units out, or about 9 billion miles or 14 billion km. The discovery will make it possible to determine the exact mass of the icy planet itself, says Brown, who is a professor at CalTech.
With the discovery of the moon of the planet now known as 2003 UB313, this means that three of the four largest KBO's known -- including Pluto, which is now generally regarded as a member of this class of small, icy bodies in the outer solar system -- have moons, Brown said. But this one "is a completely different type of satellite from anything we've seen before," Brown says, being relatively tiny and orbiting very far from its planet. It is 100 times fainter than the planet.
Brown says the new moon represents "essentially a new class of satellites to large Kuiper Belt Objects. It is tiny compared to the primary, and much fainter. We have never seen satellites like this before." A paper on the discovery is being submitted today to Atrophysical Journal Letters.
Marcos van Dam of the Keck Observatory, a co-author of the paper, says the unusual moon "suggests that these Kuiper Belt Objects may have formed differently than smaller objects in the same region."
Some have argued that rather than include newly discovered objects such as 2003 UB313 in the designation of planet, that Pluto itself should be demoted to simply another KBO, leaving just eight planets. The Rose Space Center at the American Museum of Natural Hustory in New York City has followed that approach in its displays.
The International Astronomical Union is debating the issue of how to define planets, and will not rule on a name for the new KBO or its moon until that decision is made.
The new planet 2003 UB313 takes 560 years to complete one orbit -- more than twice the length of Pluto's year. Brown will using observing time on the Hubble telescope in November and December to study the new moon's motion. "It is the only way we could ever determine the mass of Xena -- because it has a moon," he said.
Pluto and its moon Charon had been seen as the oddballs of the solar system. But now studying them along with Xena and its moon, as well as another moon recently discovered around the KBO called 2003 EL61, Brown said, "together will teach us much more about the solar system than any single oddball ever would."