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Thursday, April 26

New Earth-like planet found


You've probably picked this news item up in the newspapers or TV news yesterday. Astronomers have found an "Earth-like" planet orbiting a nearby star Gliese 581. Speculation is rife that this planet may harbour life. It's worth just reflecting on just what has been discovered and what we know about this planet.

Firstly the planet was discovered using the radial velocity method which measures the 'wobble' induced in a star by planets orbiting it. The only real information this method tells us is the orbital period of the planet and the minimum mass of the planet. From this basic information you can calculate the distance from parent start and have a reasonable statistical estimate at the actual mass of the planet. So what have we got for this new planet ?

Well we know it's probably mass is around 5 times that of the Earth, it orbits the parent star in 13 days and therefore has an orbital radius of around 0.07 astronomical units.

Moving to the next bit of deduction. . . . because the planet is only 5 Earth masses, the assumption is that it is a rocky planet and has a roughly earth type density. Using that density allows you to estimate the size of the planet, and that comes out at about 1.5 times the size of the Earth. So far so good.

Because the parent star Gliese 581 is a red dwarf it is must less powerful that our Sun (about 50 times less powerful) and therefore the so-called habitable zone of the star is much closer. The new planet falls into the presumed habitable zone, with estimated surface temperature of around 0-40 Celsius. That means that if water exists on the planet it could be liquid and as we know liquid water might be essential for life. Therefore life is a possibility on this planet.

There is obviously quite a bit of speculation to get to some of the newspaper headlines you may have read. This discovery is very important for two reasons; firstly it is the smallest extrasolar planet discovered to date, secondly it is the only extrasolar planet discovered in the habitable zone of a nearby star. However, it almost certainly will not be the last. . . . .

For more comment on this discovery check out Cumbrian Sky, and Bad Astronomy.

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