Science Saturday: Give a shout to our new planet

And make it a loud shout, because this baby is out there.

There have been several false alarms lately about a “10th planet” as scientists have picked up new bodies orbiting around in the (not so empty) void beyond Pluto. In fact, there have been so many new items found out there in Oort land, that we’ve almost become jaded. There have even been moves to have Pluto “delisted” as a planet, since it’s now clear is has so much kin in the outer Solar System.

Expect that debate to reappear, because after this week, we’re going to have to decide if we have 8 planets or 10 — this newcomer is actually bigger than Pluto.
The discovery was annouced today by Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory in Hawaii, and David Rabinowitz of Yale University. Both Pluto and the new planet (a name has been proposed, but not yet approved) have eccentric orbits (by which astronomers mean that their path around the Sun is “not even close to round”) so depending on where each is in its relative “year,” the new discovery is between two and three times as far away as Pluto. Which is far — about 97 times as far as the Earth is from the Sun.

With the discovery of this new object, and with a new generation of monster telescopes likely to spot even more distant rocks, expect the debate to rage again about what consitutes a planet. Brown’s team discovered an object about 800 miles across in 2002, and just last year found one almost as big as Pluto — both of which help start the “is Pluto a planet” ruckus.

The find will reopen the debate over what constitutes a planet since the new body is clearly part of the Kuiper belt, a swarm of rocks and asteroids orbiting the sun beyond Neptune that are probably the remains of debris that formed the solar system 5 billion years ago.

But while other Kuiper Belt objects have been smaller than Pluto — whose own status as a planet is itself in doubt — this latest discovery may have to be added to the charts on the basis of size alone.

Brown said that its sheer size in relation to the nine known planets meant that it could only be classified as a planet. … in the past seven months, the scientists have been studying the planet to estimate its size and motions. So far, they can tell only that it is at least 1.5 times bigger than Pluto, which itself has a diameter of around 1,400 miles.

This gives the discovery a size of around 3,000 km. If you’re comparing the size of this object to other planets, that puts it between Pluto and Mercury, and about 1/4 the diameter of Earth. And, because the planet is so far away and it’s difficult to tell what it’s made from, there’s a chance it could be larger.

There is, however a possibility that it is substantially larger, although it is unlikely to approach the size of Mars, which has a diameter of 4,200 miles, or Earth, which is 8,000 miles in diameter.

One year on the planet will take about 560 Earth years. In any season, it’s going to be one cold little ball, as from that distance it will be hard to pick the Sun out amongst the other stars.