While the most distant exoplanets detected until today are OGLE-05-390L b, MOA-2007-BLG-400-L b at around 6,500 & 6,000 parsecs, which roughly means ~21,190 & ~19,500 light-years away respectively, an international team of astronomers proposes a new observational method that they believe will allow the detection of exoplanets in the Andromeda galaxy (M31) that is at a distance of 2.9 million light-years from us.
A simulation of the expected microlensing event. Credit: Ingrosso et al. (2009)
The authors think that that exoplanets in the M31 galaxy may be detected with the pixel-lensing method by using telescopes making high cadence observations of an ongoing microlensing event.Although the mean mass for detectable exoplanets is about 2 MJ, even small mass exoplanets (inferior to 20 Earth masses) can cause significant deviations, which are observable with large telescopes. (read more)
Ingrosso,G., De Paolis,F., Novati,S.C., Jetzer,Ph., Nucita,A.A., Zakharov,A. F. (2009). Detection of Exoplanets in M31 with Pixel-Lensing: The Event Pa-99-N2 Case, in proceedings of the "Twelfth Marcel Grosmann Meeting", Paris.