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Kepler Can't be Fixed, but Mission Far From Over

Marcia S. Smith
Posted: 15-Aug-2013
Updated: 15-Aug-2013 11:21 PM

NASA announced today that it has abandoned efforts to restore full operational capability to its planet-hunting Kepler space telescope.   Kepler's principal investigator Bill Borucki made clear that doesn't mean the mission is over, though.

During an afternoon press conference, a reporter referred to this being the end of Kepler and Borucki bristled, replying that the mission is far from over.  "This is NOT the end of the Kepler mission," he exclaimed. The mission has two parts, making observations and analyzing the data from those observations.  It is only the acquisition of new exoplanet data that has come to an end, not the analysis. "The Kepler mission is no way done at this point," he emphasized.

Kepler was launched in 2009 and acquired four years of data.  Scientists have analyzed the first two years of that data, but still have another two years of data to go.  Borucki is very optimistic that there are many discoveries yet to be found.  So far, scientists have confirmed 135 planets orbiting other stars -- exoplanets.   The goal is to find an Earth-size planet orbiting a Sun-like star in that star's "habitable zone."  That has not been found yet.   A number of Earth-size planets have been discovered, but not within their stars' habitable zones.   Slightly larger planets have been found within habitable zones, but the stars are cooler than our Sun.  

Borucki pointed out that Kepler finds planets by observing them as they cross ("transit") the face of their star, so those found to date are close enough to make two or three orbits within the two years of data that have been analyzed.   Any planet in the habitable zone of a star like our Sun will, like Earth, take about a year to transit.  Several transits are required before a planet can be confirmed, so planets with one-year orbits hopefully will be revealed in the yet-to-be analyzed data.

Kepler no longer can acquire new exoplanet data, however.   It has four reaction wheels and three need to be operating to provide the requisite accuracy.   The modest life expectancy of these components is fairly well understood.   Not unexpectedly, one wheel failed last year and a second failed in May.  NASA engineers at Ames Research Center were trying to restore operations to one of the wheels, but ended those efforts last week.  Kepler completed its primary mission in November 2012.  NASA approved a 4-year extended mission hoping the reaction wheels would cooperate, but they did not.

Scientists are assessing whether Kepler can be used for other purposes, such as searching for asteroids or supernovae or for microlensing.   Ideas are being submitted and the Kepler team will make recommendations to NASA Headquarters about which, if any, are sufficiently practical to warrant funding if money is available.

That would be a bonus round.  Kepler already has demonstrated that there are many exoplanets in a variety of sizes orbiting a variety of types of stars.   Borucki said the Kepler data are "critically important to mankind's future" because they are one step in discovering "our place in the galaxy and what life may be out there." 

In April, NASA selected a new mission, the Transiting Exoplanet Survey Satellite (TESS), as part of its Explorer program for launch in 2017.   Led by MIT's George Ricker, TESS will search for exoplanets around the nearest and brightest stars.


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