On 6 October 1995, Didier Queloz and Michel Mayor of the Geneva Observatory in Switzerland went public with their discovery of a planet circling another sun-like star. The technique used to find that first extrasolar planet was to look for the wobble the planet made in the stars course as it moved through space. The two big problems with this technique are, first, it’s really good at finding big planets, like Jupiter, as close to a star as Mercury is to the Sun, because you get a nice big wobble, and, second, it only works out as far as 170 light years, because after that it’s too hard to track a star’s movement through space.

To use a real estate analogy, you’re much more likely to find massive inner city projects that rock the ‘hood when, deep down, you really want to know how many nice bungalows there are about ten clicks out of town. You’ve got to try something different for that, and because, as Einstein determined starlight is bent by mass, you point at the core of the galaxy with telescopes hooked up to CCDs, let the computers do the watching, and wait till you get lucky when one star, by chance, happens to get right behind another from our point of view.

When one star passes in front of another as seen from Earth, light from the background star is bent and magnified, or “lensed,” by the gravity of the foreground star, at random. If your really lucky and the star in the front is playing host to a planet, the planet’s gravity will boost the light from the background star.

About 1000 microlensing events are identified annually by an international collaboration called OGLE (Optical Gravitational Lensing Experiment) which monitors 170 million stars in the Milky Way’s central “bulge.” Astronomers in Perth, Australia, follow up these events and while doing so found a planet’s telltale signal on 9 August 2005.

There is some uncertainty in the planet’s mass: it might be as 2.8 the mass of the earth or as large as 11 times, because the method measures only the ratio of the masses of the planet and its star and the star’s mass can only be guessed from its surface temperature and estimated brightness.

The fact that they found one rocky, icy planet out of three by microlensing suggests that they are quite common, or that this was a complete fluke, but if not, it seems Earth-like worlds might be a lot more common than we thought and if so, a lot more will be turning up soon.

Check the Web for more info.

[tags]ogle,optical gravitational lensing experiment,didier queloz,michel mayor,microlensing[/tags]