Kepler Scooped! (sort of…)

By Rational Dreamer On April 21, 2009 · Leave a Comment

Just a couple of days ago I posted on this blog saying that the Kepler space telescope may already have the first Earth-like planet to be discovered—one capable of supporting life—in its sights. Well, now a team of European astronomers has made me look at little foolish by announcing that they have confirmation of the very first Earth-like planet to be located within a star’s habitable zone, before Kepler’s mission is even fully underway.

The team announced the discovery of a new exoplanet (a planet outside our own solar system), Gliese 581e, which is the lightest exoplanet ever discovered at less than twice the mass of Earth, but it takes just 3.15 days to orbit its star, and even though the star (Gliese 581) is a relatively cool red dwarf star, it is way too close and hot to have a chance of supporting life.

The Gliese 581 Solar System (Credit: ESO)

SIDE NOTE: The system astronomers use for labeling newly discovered planets around other stars can be a little confusing at first.

There are two parts to a planet’s identification:

1. The catalog name and number of the host star—in this case, Gliese 581. (Gliese is a catalog of nearby stars.)

2. A letter suffix, beginning with the letter ‘b’ in order of discovery and not distance from the sun. (‘a’ is reserved for the star, but is never used.)

So the 4th planet to be discovered in this system is Gliese 581e, even though it is probably the nearest planet to the star.

But they also announced that a previously discovered rocky planet, Gliese 581d, has an orbit of 66.8 days instead of the 83 days they had previously thought. That brings the planet in just close enough to the red dwarf for it to fall within the star’s habitable zone, meaning that liquid water might exist on the planet’s surface, and possibly even life.

But the Kepler team has not been fully scooped just yet. Today’s annoucement is a very important step on the way to discovering life on other planets, but we still haven’t found a really good Earth analog—a planet that you could call a twin of our home world. For one thing, Gliese 581d is a massive planet—a “super-Earth”, eight times the mass of Earth—and its star, the red dwarf, is very different to our Sun, being much smaller and cooler, and may have a history of violent X-ray and ultravoilet flares (as younger red dwarfs are prone to do) which might rule out any chance of life evolving within its solar system.

Either way, it’s an interesting discovery, and since Gliese 581 is only 20 light years away, we will undoubtedly learn more as we continue to study its brood of planets (now up to four in number). Indeed, we may only be a decade or so away from being able to take a direct photo of Gliese 581d’s surface, allowing us to see if it really does have any oceans.