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Planet collision could explain alien world's heat

  • 19:12 09 January 2008
  • NewScientist.com news service
  • David Shiga, Austin
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The mysterious object called 2M1207B may be a Saturn-sized planet that was recently heated up by a collision with another planet (Illustration: David Aguilar/CfA)
The mysterious object called 2M1207B may be a Saturn-sized planet that was recently heated up by a collision with another planet (Illustration: David Aguilar/CfA)
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A colossal clash of planets may explain why an alien planet 170 light years from Earth is piping hot.

Called 2M1207B, the planet was photographed in 2004 orbiting a brown dwarf, an object that is not quite heavy enough to be a normal star, but too heavy to be considered a planet.

The planet has bizarre properties that astronomers have been struggling to explain. Its light spectrum suggests it is a scorching 1300 °C. That may be because it is young – planets are hot when they first form, and indeed its brown dwarf host appears to be just 8 million years old. If so, the planet appears to be very large, since a planet would have to weigh about 8 Jupiters to retain so much heat over its lifetime.

But those estimates do not fit in with other observations. If the planet really is so large and hot, its infrared glow should be about 10 times brighter than is actually observed. Previously, a team led by Subhanjoy Mohanty of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, US, explained the discrepancy by arguing that the planet is surrounded by a dusty disc, which obscures most of the glow.

Now, two astronomers are proposing a more exotic explanation. Eric Mamajek, also of the CfA, and Michael Meyer of the University of Arizona in Tucson, US, say the planet is actually much smaller than previously believed, and is only blazing hot today because it was recently hit by another planet in the system.

"This is a strange enough object that it needs a strange explanation," says Mamajek.

Recent hit

The researchers say the planet is likely just 50,000 kilometres across, slightly smaller than Saturn. That could explain both the 1300 °C temperature and the faint infrared glow, since a larger world at the same temperature would glow more brightly simply because of its larger surface area.

But if the planet is so small, it would have long since cooled below 1300 °C. So Mamajek and Meyer propose that it heated up when it was recently smacked by another planet.

The researchers estimate that 2M1207B is a little less massive than Saturn and weighs 72 times that of Earth. If it were thumped by a planet weighing 8 Earths, the energy released would be enough to explain its heat if the collision happened within the last 100,000 years, the astronomers say.

In support of the idea, the astronomers point out that giant collisions appear to have taken place in our own solar system. The Moon, for example, is thought to have coalesced from debris produced when the Earth was hit by an object about one-tenth its mass about 4 billion years ago. Giant collisions have also been invoked to explain why Uranus's rotation axis is tilted over so much, and why Venus spins backwards compared to the other planets.

Future measurements of the planet's light spectrum could test the theory by revealing the strength of gravity on the planet's surface, and thus how massive 2M1207B really is.

The research was described on Wednesday at a meeting of the American Astronomical Society in Austin, Texas, US.

 
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"weighs" ?

By Charles

Thu Jan 10 01:39:36 GMT 2008

"The researchers estimate that 2M1207B is a little less massive than Saturn and weighs 72 times that of Earth."

Surely weight is relative to a gravity field. Shouldn't that comparison with Earth also refer to its mass?

(Also, there might be something wrong with the grammar of that sentence... :-)

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Electrical Universe Offers More Plausible Explanation

By Mike Stuart

Thu Jan 10 09:06:39 GMT 2008

Tradional astronomers think that gravity is the primary force explaining what they see in space. Their refusal to acknowledge the role of magnetic fields and electric currents in space, results in wierd anomolies that are continuously being discovered and are not explicable in terms of current gravity-focused models.

Saturn's hot spots (on its north and south poles) are a similar phenomenon. The recent discovery by THEMIS of magnetic "ropes" (i.e. Birkeland Currents) connecting the north pole of Earth to the solar wind, discharging a wopping 40,000 km/h auroral storm and 500,000 billion joules of energy, is another indication of the growing evidence that electrical forces play a much bigger role than we expected in our observations of space physics.

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