Tuesday, June 14, 2005

Earth-like planet discovery

Yesterday the planet-finding team of Paul Butler, Geoff Marcy and Debra Fischer (among many others) announced the discovery of a planet with a mass of 6-8 times the mass of the earth orbiting a nearby star. The work, headed by team member Eugenio Rivera of Lick Observatory, has been submitted for publication in The Astrophysical Journal, one of the top astronomy journals.

Here's an FAQ about the new planet:

  • How far away is the planet? The planet orbits a star, Gliese 876, which is 15 light-years (90 trillion miles, or 150 trillion km) away.
  • How do we know the planet is there? The discoverers detected a wobble in the parent star caused by the planet's gravity.
  • Are there any other planets around this star? Previously, two Juptier-sized planets were known to exist around this star.
  • Is there any chance of life on this planet? Almost certainly not. The planet orbits very close to the parent star, about ten times closer than Mercury is to the sun. It's surface temperature is likely between 400 and 800 degrees Fahrenheit, or almost as hot as Venus!
  • Why is this planet exciting? This planet is hot enough that it very likely could not hold on to a large atmosphere. Most of the mass of Jupiter, Saturn, Uranus and Neptune resides in the atmosphere. For the new planet, most if not all of the mass is probably pure rock, like the Earth, Venus, Mercury and Mars. This would be the first planet outside the solar system known to be made of rock.

A caveat, though, is that the Geneva planet search team claimed to find a rocky planet last year (see my blog post on the "super Earth"). So one could argue (and I'm sure astronomers are!) whether this is the first discovery of a rocky planet around another star. The reality is that we really don't know what these two planets look like or are made of. Future space missions that will actually be able to take pictures of these planets will help us to tell how big the planets are, allowing us to tell if they are made of rocks or gas.

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