Microlensing might detect planets as well as MACHOs

[marcus]

massive compact halo objects have been detected by microlensing

an invisible compact object passing in front of a distant source causes a temporary spike in the light curve by gravitational lensing---the brightening might last a couple of days

this was written about in the late 1990s when they wanted an upper bound on the contribution of MACHO to dark matter and a bunch of invisible massive objects were observed

but wait! the story isn't over apparently. I recently came across a page of some people who think they can detect earth-size and larger-size planets by a "double spike" microlensing effect.

the star causes a large broad blip in the lightcurve and the planet causes a smaller sharp blip superimposed on it.

I cannot vouch for this. It may not be a reliable webpage. It has a lot of links to established microlensing searches and established planet searches, so it might be a useful page as well as being a curiosity. The page is called "Microlensing Planet Search". Tell me if you think it has any interest or is just weird

http://bustard.phys.nd.edu/MPS/

 

[Nereid]

It's not wierd, but the detection rate would be pretty low, even if there were lots and lots of planets. Planets orbit in a plane, so the path of lensing object (as seen by us) would need to be in (or sufficiently close to) the orbital plane.

IIRC, there was quite a lot of excitement over the light curve of a caustic crossing lens event, some saw it as evidence of a planet.