Kepler Scooped! (sort of…)

Rational Dreamer — Wed, 22 Apr 2009 05:44:14 +0000

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.

First Light!

Rational Dreamer — Mon, 20 Apr 2009 08:29:17 +0000

This is a very cool image. In fact, it’s hard to describe in mere words how cool this picture really is. What you’re looking at is the first image beamed down from the Kepler space telescope, launched into orbit around the Sun (trailing Earth’s orbit) just over a month ago. You can just imagine standing on the bridge of some futuristic spaceship and looking out onto such a scene as this. But the really cool thing about this image is that in all probability, the first ever Earth-like planet we discover outside our own Solar System is somewhere within this picture.

Kepler’s three-and-a-half-year mission is to stare unblinkingly at this one patch of the heavens and detect the slightest dimming of any of the 100,000 target stars within it. If they detect a brief drop in a star’s brightness, and that drop is repeated two more times at regular intervals, then there is a very good chance that the dimming of the star’s light is being caused by a planet passing between us and the star (called a transit) and blocking out a small amount of the light.

Kepler’s camera is the largest ever launched into space. The image you see above is 95 megapixels in size, and the detectors are so sensitive that they expect to be able to discover planets that are up to 1,500 light years away, which is simply astounding.

One of the first things they plan to do is to see if they can detect a planet that has already been discovered by telescopes here on Earth. It is a “hot jupiter” which simply means that it’s a gas giant, like our own planet Jupiter, and it orbits very close to it’s parent star—much closer than Mercury, in fact. It’s so close that it only takes 2.5 days to complete an orbit, so the planet crosses in front of the star about three times a week, each time causing a slight dip in the amount of starlight reaching Kepler’s camera. So we should know very soon if the spacecraft can do what it was designed to do.

Once they have confirmed that they can detect hot jupiters, the mission team will be settling in for the long haul. While the main goal of the mission is to discover as many planets as they can of any size, the holy grail would be to discover an Earth-like planet (i.e. a planet about the same size and mass as our world) orbiting at about the same distance from its star as the Earth is from the Sun. In other words, detecting a planet that might be capable of supporting life. Of course, that means the transits and the resulting dips in the starlight will only occur once every 12 months or so, and since they need to detect three of these transits to confirm that the dimming is being caused by a planet, it will be at least three years before any major discoveries can be announced.

There is always a chance that they don’t discover any Earth-like planets at all, and that would be a major disappointment but, as the title of this blog suggests, we can always dream!

Rational Dreaming » Kepler

Kepler Scooped! (sort of…)

First Light!