1000th exoplanet discovered!

It's been a long journey since the discovery of the first planet outside our solar system back in 1995.  That discovery, of the planet 51 Peg b, proved what astronomers knew all along - that the Sun was not unique among stars in the galaxy in hosting planets.  Since then, we've begun to find planets nearly everywhere we look.  Our Sun isn't even one among a lucky few - it seems as if the galaxy is overflowing with planets.

Kepler candidate planets superimposed over an image of the region of sky viewed by the telescope.  Planets seem to be everywhere we look!  (Image credit: NASA)

That this is planet 1,000 might come as a surprise to some.  After all, hasn't Kepler alone discovered thousands of planets?  Yes, and no.  To date, Kepler has identified more than 3,000 "candidate" planets and there is much more data yet to examine.  Of those thousands of candidates, though, only a little over 100 have been confirmed as planets (most confirmed planets have been detected by other methods).  That's because detections by Kepler could be things other than planets.  For example, the dip in a star's brightness that usually indicates a planet passing in front of it could also be the result of a star spot.  Although the Kepler team are pretty good at screening these out, to be sure we've got a planet a separate confirmation is needed.

These confirmations are usually performed using the radial-velocity method.  This method looks for tiny changes in the color of a star's light as it wobbles back and forth because of a planet.  Phenomena that can fool the transit method used by Kepler can't also fool the radial velocity technique.  This allows astronomers to assert with relative confidence that they have found a planet.  Unfortunately, taking radial-velocity measurements is not easy and lags far behind the observations made by Kepler.

The first thousand planets have revealed an incredible diversity in the sizes, orbits, and compositions of these alien worlds.  They forced a fundamental reimagining of how planets form, a process that is very much ongoing today.  With the next thousand, or ten thousand, or one hundred thousand, we will start to build up a true understanding of how our solar system fits in the grand scheme of the Milky Way.  What could be more exciting than that?