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NASA's Kepler Space Telescope will resume its hunt for exoplanets in K2 mission

By Scott Sutherland
Meteorologist/Science Writer
Sunday, May 18, 2014, 3:10 PM

NASA's Kepler Space Telescope, a marvel of technology that has already helped astronomers find nearly 1,000 confirmed alien worlds and close to four times that many candidate worlds, suffered a critical failure in 2013 that put it out of action. Now, due to some impressive ingenuity by the scientists and engineers on the Kepler team, this mission is getting a second chance.

Kepler detects planets by watching a particular patch of space and carefully recording the brightness of the stars in its view. Any time that one of these stars dims significantly, there's a good chance that the telescope just spotted a planet passing between it and the star. This is called a transit. However, in order for it to properly see these transits, Kepler's detectors must remain absolutely still, even though the spacecraft itself was being pushed by radiation pressure from the Sun. It did this through the use of four 'reaction wheels' that smoothly adjusted the position of the detector array to compensate for movements of the spacecraft. Kepler only needed three of these wheels to operate, with the fourth as a spare, but by early 2013, it had already lost the use of one and another was suffering problems. By May 2013, the situation had become worse, and the Kepler team had to stop gathering data altogether.

Credit: NASA Ames/W Stenzel

Credit: NASA Ames/W Stenzel

Although Kepler's original mission was forced to end, the team began searching for something new for the telescope to do, but in the process, they were actually figured out a way for it to continue to look for extrasolar planets (exoplanets). Rather than use reaction wheels to steady itself against the radiation pressure, the telescope would use that very radiation pressure as the means to steady itself. Since the telescope's solar panels wrap around the spacecraft and are symmetrical on either side of a ridge that runs nearly the length of the spacecraft, if that ridge is pointed directly at the Sun, the radiation pressure will push on both sides of the telescope equally and hold it steady enough that it can once again look for planetary transits. 

The only catch to this is that, unlike before, when the telescope remained pointed at one specific region of space (near the constellation Cygnus), the K2 mission (shown to the right and on the NASA website) will now scan along our solar system's ecliptic (also called the zodiac), changing its view every 75 days so that it doesn't catch our Sun's rays on its detectors (which would burn them out). This will limit what types of planets Kepler will be able to see, since it will be harder to see planets with longer orbits. However, it will actually be able to scan more of the space around us, giving us an even better idea of just how many alien worlds are out there. 

As of today, Kepler has already discovered 966 confirmed exoplanets, with another 3,845 possible ones awaiting confirmation by telescopes on the ground, and that's just from a fraction of the data from Kepler's first four years in orbit. Astronomers and citizen scientists are still poring over that data, and this new K2 mission begins May 30, and has now been funded through 2016, so it will add even more chances to find the alien worlds around us. 

You can keep track of Kepler's discoveries on the NASA website for the mission, and if you'd like to actually help search the data for planets, you can participate on PlanetHunters.org.

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