Free Astronomy Magazine September-October 2016

PLANETOLOGY the most exciting hunt for exoplanets con- ducted that far. In about four years of sur- veys, Kepler had found more than 4,000 candidate planets, half of which were val- idated (it is almost certain that they are planets) or confirmed (i.e., their masses are known) through in-depth observations con- ducted with large telescopes on Earth. The dismay of not being able to continue the original mission (just when Earth-sized planets on orbits like ours, around stars similar to the Sun, were beginning to be discovered) did not, though, last long, as NASA engineers quickly planned a phoenix- like resurrection for Kepler: a new mis- sion that began in May 2014 for which were sufficient the other two functioning gyro- scopes and the Sun’s radiation pressure, i.e., the strict minimum needed to keep the in- strument pointed in the direction of the ecliptic and no longer observe just a restrict- ed patch of the heavens, but various re- gions along a band of the sky. The second Kepler mission, called K2, differs from the first in some significant details. In fact, it has as target more types of stars, as in addition to sun-like stars there are now also red-dwarf type stars and, given that it covers a more diverse and wider sky region and that red dwarfs are more predominant in the Milky Way, the telescope is now looking for exoplanets that are on average closer to Earth compared to before. Also the forced orientation on the ecliptic has a positive T his image taken on 20 October 2014 gives an idea of how Kepler’s sen- sor is made. It consists of various pairs of adjacent CCDs, with blind areas on the bor- ders. On this occa- sion, two pairs failed to produce any signal. In a corner of the first element (upper left) we can see the image left by the Siding Spring comet. [NASA Ames/W. Stenzel; SETI Institute/ D. Caldwell] On the side, a photomontage with the approxi- mate location of the latest validat- ed exoplanets. [K. Teramura (UHIfA) et al., NASA]