Microlensing

Microlensing is an event that occurs when an object with enough mass—typically an orbiting star or even a black hole—passes between our line of sight and a background star. The strong gravitational pull of the object bends light rays from the distant star, magnifying that light as a lens would. A person sees the star become brighter as the “lens” passes in front. An extra solar planet will act like a tiny defect on the light curve of the star it is orbiting.

The discovery of OGLE 2005-BLG-390Lb, the first cool rocky/icy extrasolar planet, first brought to mind the high sensitivity of the microlensing technique, because the planet is less than 10 Earth-masses. Now astronomers are using the technique to search for earth-sized planets, and astronomers are hopeful. “Even a signal from an earth-mass planet can be relatively large—tens of percent, which is very detectable,” noted astronomer Scott Gaudi, a pioneer in microlensing techniques.

A microlensing “event” can last days, but the planet’s presence only changes the signal for about one day. Therefore, the data collected needs to be analyzed quickly to notice any possible changes from a planet. The Microlensing Follow Up Network, dubbed MicroFUN, gathers data from observatories around the world to monitor microlensing events around-the-clock. Additionally, an automated anomaly detector, which went into operation for the 2007 microlensing observing season, experiences immediate feedback provided by robotic telescopes.

With such a large effort directed toward microlensing, there is a fair chance of detecting an earth-size planet in the coming years. This could be possible with an intricate network of wide-field telescopes or a space-based telescope. The detection limit of gravitational microlensing extends below 0.1 Earth-masses, which is very promising for finding the coveted earth-sized planets.