January 18, 2008

When Planets Collide

170 light-years away from earth exists a particularly puzzling orbiting object. This object, 2M1207B, seems to be physically impossible. Nothing about it matches any established astronomical theory.

Eric Mamajek of the Harvard-Smithsonian Center for Astrophysics announced in a press conference, "This is a strange enough object that it needs a strange explanation." During this press conference, the 211th meeting of the American Astronomical Society, astronomers announced that 2M1207B might in fact be the merger of two protoplanets.

This object orbits a brown dwarf called 2M1207A which is approximately 8 million years old, very young. This means that 2M1207B should also be close to 8 million years old. However, this seems impossible because the object is not nearly as cool as it should be; in fact it is 1100 degrees Fahrenheit hotter than it should be. This extra heat is what gave scientists the clue that a protoplanetary collision may have occurred.

Mamajek explained, ""Most, if not all, planets in our Solar System were hit early in their history. A collision created Earth's Moon and knocked Uranus on its side. It's quite likely that major collisions happen in other young planetary systems, too."

Because of its high temperature, a certain luminosity is expected of 2M1207B but it is not nearly as bright as expected. Scientists thought perhaps it might be obscured by dust. Mamajek along with Michael Meyer of the University of Arizona thought differently. They proposed that 2M1207B is approximately the size of Saturn, and being small has a small surface area that puts off energy.

In their proposal they calculated 2M1207B to have a radius of 31,000 miles, 6,000 miles less than that of Saturn and a mass about 80 times that of Earth. In order for an object this size to remain so hot, a collision must have been the source of its heat. Meyer and Mamajek claim that 2M1207B might be the result of a collision between a planet about three times the size of Earth and a gas planet the size of Saturn.

Meyer explained, "The Earth was hit by something one-tenth its mass, and it's likely that other planets in our solar system were too, including Venus and Uranus. If that one-tenth scale holds in other planetary systems, then we could be seeing the aftermath of a collision between a 72 Earth-mass gas giant and an 8 Earth-mass planet, even though such collisions are very unlikely."

The theory actually has the potential to check out from a timeline point of view, and it also hypothesizes statements that can be tested by astronomers. Within the next few years, more answers should be available. Mamajek credits the next generation of ground-based telescopes for these possibilities.

Even if all of Mamajek's theories are incorrect, he strongly believes that there will be some clear-cut answers within ten years.


Photo Caption: Illustrated here in this artist's concept, astronomers may have observed the aftermath of a collision between two protoplanets, one Jupiter-sized and one Neptune-sized, in the system 2M1207. Credit: David A. Aguilar (Harvard-Smithsonian CfA)


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