My God, it’s full of planets!

The latest batch of results from Kepler is both illuminating and baffling

 

 

WHEN it comes to public appreciation of astronomy, NASA’s exoplanet-hunting space telescope Kepler is the most successful instrument the agency has launched since Hubble. Astronomers have been spotting exoplanets—those that orbit stars other than the sun—since the 1990s. But Kepler has transformed the field from a cottage industry into a production line.
On November 4th astronomers gathered at NASA’s Ames research centre, in California, to hear the latest news. The headline was the release of the most recent batch of data from the spacecraft. The 833 new planets thus identified bring the total found by Kepler to 3,538. Technically these are only “candidate” planets, whose presence is inferred by the tiny dimming they cause when they pass in front of their host stars. Such candidates must await confirmation by other telescopes before being promoted to full discoveries. But astronomers expect a low rate of false positives.
This exoplanetary smorgasbord allows researchers to conduct statistical analyses and extrapolate Kepler’s results to the rest of the galaxy. A group led by Erik Petigura of the University of California, Berkeley, having crunched the numbers, told the meeting that around a fifth of sun-like stars in the Milky Way are likely to host planets roughly the size and temperature of Earth. By the researchers’ definition, sun-like stars are a fifth of the total, so that means only about one star in 25 would have such a planet. But the galaxy is a big place, so if they are right there are billions of Earthlike planets in it. The closest is expected to be less than 12 light-years from Earth.
Although the search for Earthlike planets gets most of the limelight, Kepler’s data are useful for other things, too. They have, for instance, driven an empirical coach and horses through astronomers’ ideas about how planets form, by finding all sorts of objects that should not, according to the old theories, exist at all—such as planets the size of Jupiter or bigger orbiting close to their parent stars. Building a new theory to account for these space oddities is a big project. Other work has used the telescope for asteroseismology, the study of “starquakes”, which are surface disturbances whose existence can be inferred by fluctuations in a star’s brightness, and which reveal details of its inner structure.
Amid the excitement, there was a bittersweet quality to the meeting. In May Kepler suffered a malfunction and it is now crippled—unable to point itself reliably in the right direction. In April, however, NASA had announced a successor mission, the Transiting Exoplanet Survey Satellite, due to launch in 2017 and designed to search stars near Earth for signs of planets that might, one day, yield to direct telescopic inspection. If Kepler’s results are anything to go by, it should find plenty.

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