A remarkable technological fix has revived the Kepler Space Telescope, and it is once again finding planets beyond our solar system. So far, it has yet to match the astonishing feats of its earlier mission, when hundreds of likely planets were announced at a time. Nevertheless, the announcement that the telescope has found its first new exoplanet since the wheels literally came off is cause for celebration.
Early discoveries of planets circling other stars were made using the Doppler "wobble method." While this is still used today to find planets around relatively nearby stars, it is a slow process.
Kepler, on the other hand, has detected 996 confirmed exoplanets, and 3,216 that have yet to be verified. It did so through exceptionally sensitive measurements of the light coming from 145,000 stars. When planets pass in front of these stars they dim slightly, and where this happens regularly enough, Kepler can determine the planet's orbital period.
The wealth of data Kepler produced has allowed astronomers to calculate the frequency of planetary systems in the galaxy, as well as pick up some particularly exciting examples. However, two of the reaction wheels that kept the telescope pointing in the right direction in the absence of gravity failed, ending observations in 2013.
Most of the exoplanet announcements came after this, as the data took a while to process, but the original mission was over. This, however, was not the end of Kepler's capacity. NASA put out a call for suggestions on how the disabled, but not destroyed, spacecraft could be put to use, and in November 2013 adopted the K2 proposal to shift its focus. K2 relies on the pressure of sunlight to create what astronomers are calling a “virtual reaction wheel.”
Credit: NASA. Kepler is bracing itself against the pressure of sunlight to remain stable enough to take useful observations.
Kepler is now only one-fifteenth as precise as its earliest incarnation, but that is still enough to make observations of asteroids and comets within our solar system, as well as to trace the decline of supernovae. Moreover, it was thought possible that this lower precision might still be enough to find planets around red dwarf stars, even if the main sequence stars on which Kepler initially focused were now out of reach.
And so it has been proven. Phoenix-like, Kepler is back, with NASA announcing the confirmation of a potential planet, HIP 116454b, located during a test run in February. HIP 116454b lies 180 light-years from Earth toward the constellation Pisces and is around 2.5 times the diameter of Earth. Its existence was confirmed by the Telescopio Nazionale Galileo in the Canary Islands.
"The Kepler mission showed us that planets larger in size than Earth and smaller than Neptune are common in the galaxy, yet they are absent in our solar system," said NASA's Steve Howell. "K2 is uniquely positioned to dramatically refine our understanding of these alien worlds and further define the boundary between rocky worlds like Earth and ice giants like Neptune."
The work has been accepted for publication in The Astrophysical Journal. Meanwhile, space scientists are working on expanding Kepler's capacities, with a focus on nearby stars.