By Nick Gautier, Kepler Deputy Project Scientist
On May 14th, the Kepler spacecraft suffered its second reaction wheel failure and autonomously entered thruster-controlled safe mode. Since the Kepler spacecraft cannot point itself accurately with only the two remaining reaction wheels, the Kepler team has stopped data collection and has placed the Kepler spacecraft in a configuration called Point Rest State that keeps the spacecraft in a safe attitude, allows for continuous communication, and provides for very low fuel usage.
While this second wheel failure is disappointing, Kepler had already successfully completed its baseline mission of 3 ½ years of observations last November and exceeded its design mission lifetime of four years.
The Kepler team is currently evaluating possibilities for recovering sufficient pointing accuracy to continue the exoplanet survey or, if full performance is not recoverable, to enable additional science.
Analysis of the situation and implementation of any recovery strategy will take some time. An initial assessment has been made but it will likely take weeks to develop, test, and implement new procedures and techniques that might be used to attempt to recover pointing functionality.
The second wheel failure does not mean that the Kepler mission is over. Kepler has collected just over four years of exoplanet survey data but has thoroughly analyzed only two years of data. Full analysis of all four years of data over the coming months will continue to add to the huge number of exoplanets and exoplanet candidates that Kepler has already delivered. The touchstone for the Kepler exoplanet survey, discovery of a close analog to our own planet Earth, may well lurk in the last two years of observations.
New Kepler results were delivered to the NASA Exoplanet Archive on May 28 in the form of 1,924 new Kepler Objects of Interest (KOIs). In keeping with the Project policy of releasing Kepler data and results as rapidly as possible during the Kepler Extended Mission, these new KOIs were delivered in a less thoroughly analyzed state than previous KOIs. The new KOIs are truly just what their name implies: objects of interest that may or may not turn out to be actual exoplanets. Previously released KOIs had undergone thorough analyses that weeded out most false positives (phenomena masquerading as true planets). Those KOI lists were expected to be more than 90% actual exoplanets. The recent batch of 1,924 will have many more false positives and may be no more than 50% true exoplanets. However, the Kepler team continues to analyze all KOIs and 503 of the new batch have been identified as more than 90% likely to be real exoplanets. KOIs that have not undergone thorough analysis are marked as “not dispositioned” in the tables at the Exoplanet Archive.