2003 UB313: Tenth Planet is Discovered

Time lapse Photograph of 2003UB313 pictured above. Courtesy Mike Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University).

Who discovered UB313?

The object has been tracked since October 31, 2003 by Professor Mike Brown at the California Institute of Technology and his colleagues (Chad Trujillo of Gemini Observatory in Mauna Kea, Hawaii, and David Rabinowitz of yale University). Although it was observed with other telescopes, it was not determined to be a planet until its motion was tracked using the Palomar Observatory's Samuel Oschin telescope. The planetary nature of the object's motion was determined as of January 8, 2005. News of the discovery was released by CalTech on July 29, 2005.

How large is this body?

Brown estimates that UB313 is somewhere between 2390 and 3550 km in diameter. This would make it approximately one and a half times the size of Pluto. Since the reflectance of the planet (percent of light it reflects) is not yet determined, it is not yet possible to measure its size exactly. However, even is the planet was found to have 100% reflectance, it would still be larger than pluto. Hence the team is confident the object is a planet.

How far away is the planet?

The object currently lies nine billion miles from earth. Currently the object is approximately 97 astronomical units from the sun (about 97 times further from the sun than Earth is).

Where can it be seen?

UB313 is currently almost directly overhead in the early-morning eastern sky, in the Cetus constellation. It will be visible over the next 6 months using high-powered telescopes.

What is the composition of this object?

The celestial body appears to be covered in methane ice.

What will be the new name?

The discoverers have submitted a proposal to the International Astronomical Union. Speculators have promoted the planet as "Xena" and "Lila." Xena was used as a nickname by the discoverers, and Lila is Mike Brown's babl daughter's name. However, Mike states that he cannot reveal the proposed name. Unfortunately, the seemingly logical choice of "Persephone" (wife of pluto who was kidnapped) has already been given to an asteroid.

Why has it not been discovered until now?

The 10th planet's orbit is at a 45-degree angle to the rest of the solar system, in what is known as the Kuiper Belt. Hence, it was in a location where very few would search for a planet. According to Brown, news of the discovery was announced earlier than expected after hackers broke into his website and stole news of it. The team had planned to keep the news secret until their research was completed.