Kepler Spacecraft in Emergency Mode

The last regular contact with the spacecraft was on April. 4.  The spacecraft was in good health and operating as expected.

Kepler completed its prime mission in 2012, detecting nearly 5,000 exoplanets, of which, more than 1,000 have been confirmed. In 2014 the Kepler spacecraft began a new mission called K2. In this extended mission, K2 continues the search for exoplanets while introducing new research opportunities to study young stars, supernovae, and many other astronomical objects.

Source: Mission Manager Update: Kepler Spacecraft in Emergency Mode | NASA

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To save on bandwidth, Kepler only downlinks data from the pixels associated with 156,000 target stars out of the millions of stars in the Kepler field.  Data from an “aperture” of pixels around each target star are downlinked to Earth, and computer programs on Earth measure the brightness of the star based on the light that hit the pixels in the aperture.  If the telescope pointing is not good enough to keep the target stars in their respective apertures on the pixels, it is impossible to measure the brightness of those stars with a precision of 20 parts per million.

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Once the spacecraft checks out, Kepler will kick off its latest effort, looking toward the galactic center for planets whose gravity distorts the light from far more distant stars. This technique, known as gravitational microlensing, has been used with ground-based telescopes to discover about 46 planets, some of them orphaned from their parent stars. But the method is a first for Kepler, which searches for dips in starlight caused by planets crossing in front of their suns.