During a scheduled semi-weekly contact on May 30, 2013, the spacecraft experienced another safe mode in response to a star tracker anomaly, but was returned to PRS in a matter of hours. The star trackers have historically lost their lock on stars from time to time throughout the prime mission, so this was not a big surprise. However, it appears that the spacecraft may be more susceptible to these errors when not fine-point, where it collects science data. The team expects to make adjustments to onboard fault parameters to limit this kind of event, though it is not considered serious. This star-tracker anomaly is not related to the reaction wheels failures.
With the spacecraft in PRS, its immediate safety is no longer an urgent concern, so an Anomaly Response Team has been formed to manage the wheel recovery efforts. This team has already identified a number of tests to run on the malfunctioning wheels to assess the degree of stiction and the likelihood of freeing a wheel. They are working with the mission engineers to develop and test the commands on the spacecraft test bed located at Ball Aerospace in Boulder, Colo. It will likely be several weeks before they are ready to implement the commands on the reaction wheels aboard the spacecraft. We will continue to provide updates on significant changes as these plans develop and mature.
Analysis of the Kepler data continues. Last week the team delivered 1,924 new Kepler Objects of Interest (KOIs) to the NASA Exoplanet Archive. The new KOIs were found by searching the observational data from Quarters 1 to Quarter 12. Of the 1,924 new KOIs, 503 already have been dispositioned as planet candidates, while many others are destined to become false positives. These newly announced planet candidates bring the current count of Kepler planet candidates to 3,216. Some of these new planet candidates are small and some reside in the habitable zone of their stars, but much work remains to be done to verify these results. The team continues to assess and disposition the remaining KOIs. To watch the results of this process unfold, or for details on specific KOIs, see the Q1-Q12 KOI activity table at the NASA Exoplanet Archive.
Results based on Kepler data were prominently featured at the 222nd meeting of the American Astronomical Society held June 2-6, 2013 in Indianapolis, Ind. Steve Howell, Kepler project scientist at NASA Ames Research Center at Moffett Field, Calif., presented a new study that suggests many of the stars in the Kepler field of view may be somewhat larger than previously thought. The research team, led by Mark Everett, postdoctoral research associate at the National Optical Astronomy Observatory in Tucson, Ariz., used spectroscopy which separates a star's light into its component colors, to more accurately measure the star's size, temperature, brightness and metallicity. This multi-year stellar classification study included observations over 48 nights of approximately 270 stars. The findings indicate that a significant fraction of the 270 stars observed are larger than previously thought. Since planet sizes are measured relative to the stars, the analysis yields revised planet properties as well. The size estimates of many of the planets associated with these 270 stars have increased. This is yet another example illustrating the importance of stellar spectroscopy for fine-tuning the properties of Kepler planet candidates.