David Charbonneau of Harvard gave an outstanding talk the other day at Penn on “The Fast Track to Finding an Inhabited Exoplanet.” While the title is (presumably intentionally) provocative, the science he described is amazing.
A lot of attention has been given to the Kepler mission, and in particular, its discovery of approximately 1200 candidate exoplanets. Kepler is somewhat different than most previous planet searches. Historically, most planets were discovered by looking for the wobble in a star as the star and planet orbited around their center of mass. With Kepler, the idea is to observe a dip in brightness in the light from the sun as the planet passes in front of it:
That’s some actual data right there. The wobble method gives you the mass of the planet, while the light curve gives you the size. If you’re looking, specifically, for earth-like planets, size really matters.
What Charbonneau really wanted to tell us about what a project that he’s leading up at Harvard (and observing in Arizona) called MEarth. They wanted to specifically focus on the possibility of finding not only earth-like masses and sizes, not only planets in the Habitable Zone, but also to find planets with atmospheres potentially conducive to, or already supporting life.
One thing that you need to understand about planet hunting is that you never get to resolve the planet and the star separately, only the combined light of the two. What MEarth aims to do (and has done, with one planet so far) is to measure the light coming off the planet itself. If you do this at different times during the cycle, you can determine all sorts of things, including:
- Temperature across the planetary surface
- Thickness of the atmosphere
- Composition of the atmosphere
In short, you can tell a hell of a lot about the planet.
Their strategy is really cool, too. Rather than just looking at stars like our sun, they’re exclusively targeting small, M-type stars. The cool thing about these is that because they are dim, the effect of a partially eclipsing planet will be easier to detect. In addition, the Habitable zone for those stars will be much closer in, making orbits much shorter.
Perhaps the coolest thing, visually, is that it’s all run by robots. They have a dozen small telescopes out in Arizona, all robotically controlled. Click here, here, or here to see the robots in action.
It’s actually a little eerie. It’s as if at some point, the robots may decide to stop searching for exoplanets and simply take over this one.