New "Planet X" Is Definitely Larger than Pluto

Good news for textbook publishers! Astronomy textbooks will soon be rewritten following confirmation that a new object discovered at the edge of the solar system is bigger than the ninth planet, Pluto.


"Planet X" was discovered in 2005 by Professor Mike Brown and colleagues at CalTech found UB313 in January 2005 and tentatively named it 2003 UB313. These findings are bolstered by the finding by a group of German astrophysicists.

By measuring its thermal emission, the scientists were able to determine a diameter of about 3000 km, which makes it 700 km larger than Pluto.

This most distant object ever seen in the Solar System is also the largest solar system object found since the discovery of Neptune in 1846.

The findings could mean that either there will now be 10 planets in the solar system or that the status of Pluto will be downgraded and we will be back to having eight planets.

The object, given nicknames such as "Xena", "Santa" and "Rudolph", will almost certainly be named after a Greco-Roman deity who has so far not been used to describe other planets or asteroids.

The International Astronomical Union will meet this year to decide whether UB313 should be considered the 10th planet and, if so, what name it should be given.

Both Pluto and UB313 belong to the Kuiper Belt, a ring of some 100,000 objects on the outskirts of the solar system, beyond Neptune at distances over 4 billion km from the sun, over 30 times the distance between Earth and Sun.

The Kuiper Belt contains debris from the birth of the solar system. Think of it as an archaeological site containing remnants of the solar nebula from which the Sun and the planets formed.

The existence of this ring of small planetary objects was first suggested by the astronomers Kenneth Edgeworth (1880-1972) and Gerard P. Kuiper (1905-1973), but the first discovery of a "Kuiper belt object" was not until 1992.

UB313 is somewhat different from the normal Kuiper belt in that its orbit is highly excentric and 45 degrees inclined to the ecliptic plane of the planets and Kuiper Belt. It is likely that is originated in the Kuiper Belt and was deflected to its inclined orbit by Neptune.

Over 700 Kuiper belt objects have been found, the most popular besides Pluto and it's companion Charon are called Sedna and Quaoar.

New Planet is Larger Than Pluto: Press Release

David Jewitt's Kuiper Belt Page