On the retirement of Kepler

Article written by: Gavin Ramsay, Resident Astronomer Armagh Observatory and Planetarium

NASA has announced the retirement of the Kepler spacecraft. After launch in March 2009, it began a continuous observation of a 115 square degree field of view (the diameter of the moon is 1/2 a degree) between the constellations Cygnus and Lyra. For all ground based telescopes, and for most space telescopes,  observations of a specific star are interrupted by either day light, bad weather or times when the Earth or Sun gets in the way. Kepler was able to make uninterrupted observations of more than 120,000 stars simultaneously with one highly accurate brightness measurement for each star every 30 min and in some cases every minute. During the four year lifetime, it discovered more than a thousand confirmed planets around other stars; allowed astronomers to penetrate deep into stars interiors through their pulsations; observe flares from stars, and outbursts from accreting binaries – to name just a few of the many science areas which Kepler data was used for.

Evidence for planets around other stars can be found if the planets orbit crosses our line of sight to the host star once per planet year. Smaller planets cause a smaller drop in light. Credit: NASA.

In May 2013, a second reaction wheel on the spacecraft failed making it very difficult to keep the satellite accurately pointed. NASA, with the help of Ball Aerospace, came up with a plan that would use the pressure of sunlight to keep the satellite correctly pointed. A new mission, K2, was devised which allowed observations of fields along the ecliptic (the path the Sun and Moon follow on the sky) to be made continuously for up to 80 days. By the end of K2 in October 2018, 18 fields had been observed in this way.

Kepler observations of the low mass star KIC 9726699 which rotates once every 12 hrs. Flares are seen once every few hours. Credit: Gavin Ramsay.

Armagh staff and students have been using data from the Kepler mission to study different types of stars. Lauren Doyle, one of our PhD students, has been using data from the mission to study flares from low mass stars. By measuring the time flares are observed, she was able to come to the surprising conclusion that the flares do not seem to be associated with the large spots (similar to Sunspots) that are known to exist on these low mass stars. This implies that flares from these low mass stars are powered in a different way from flares seen from our Sun. Lauren and others at Armagh will be using data from the NASA TESS mission which got launched in April 2018, and then the European Space Agency’s Plato mission expected to be launched in 2026.

The launch of the TESS satellite in April 2018 from Florida. Credit: NASA TV

Armagh has some insiders in the Kepler mission. Tom Barclay did his PhD with Gavin Ramsay in Armagh leaving in 2011 to work for the Kepler mission, eventually becoming the Director of the Kepler Guest Observer Facility. After Tom left to work for the TESS mission, Geert Barentsen, who also did his PhD at Armagh with Jorick Vink, succeeded Tom as their Director.