Transiting the Exoplanet Search: From Kepler to TESS

Overview

The Kepler spacecraft has observed 200,000 stars in a patch of sky in the Cygnus and Lyra constellations over a period of four years. Using knowledge gained from Kepler discoveries on the distribution of planet populations, scientists can estimate the occurrence rates of habitable Earth-sized planets within our galaxy. As the Kepler primary mission draws to an end, a new mission—the Transiting Exoplanet Survey Satellite (TESS)—is just beginning to take shape. The purpose of this follow-up mission will be to survey the entire sky looking for exoplanets that are good candidates for performing detailed characterizations of the planets and their atmospheres.

Project Details

The telescope on board the Kepler spacecraft has a 1.1-meter mirror and a 95-megapixel camera. Pixel brightness, which is used to detect planet size, is accumulated over 30-minute periods. The spacecraft is located in an Earth-trailing orbit—instead of orbiting Earth itself, the observatory trails behind Earth as it orbits the Sun. Its remote location does not permit downloading all the pixels at once, so the Kepler team selects a number of target stars representing about 5% of the total pixels and downloads them to the Kepler Science Operations Center (SOC) at NASA's Ames Research Center. These pixels are then calibrated and combined to form light curves, and scientists search for a dimming in the brightness of the stars that indicates a transiting exoplanet.

Picking up where Kepler left off, the new TESS spacecraft, planned for launch in 2017, will be in a highly elliptical orbit looking at the brightness of more than 500,000 stars during a two-year mission. Every 27 days, TESS will observe a 96-degree swath of sky (a set of observing sectors), and after two years, TESS will have observed almost the entire sky. The goal of this mission is complementary to Kepler's: While Kepler captured a statistically diverse sample of planets, TESS will focus on planets that are good candidates for further characterization by the James Webb Space Telescope.

Results and Impact

Kepler data has yielded a trove of tremendous discoveries in the field of exoplanet science: As of November 1, 2014, there are 989 confirmed or validated planets, 4,234 planet candidates, 2,165 eclipsing binary stars, and the first Earth-sized habitable zone planet, Kepler-186f. Now that SOC scientists have a sufficiently large sample size, they can perform statistics on this population of discoveries to estimate the occurrence rates of planets. Of particular interest are Earth-sized planets in the habitable zone. By estimating the occurrence rate of these planets it may one day be possible to estimate the number of life-bearing worlds in the universe.

Why HPC Matters

This year, for the first time, we were able to recalibrate all the pixels ever collected by Kepler, using the Pleiades supercomputer at the NASA Advanced Supercomputing facility at NASA Ames. This will be the cleanest dataset ever produced by the Kepler team as we incorporate the results of our best algorithms for removing noise from various sources (instruments, cosmic rays, stars). We will then search this new dataset for additional planet candidates. The Kepler science pipeline searches 200,000 stars observed by Kepler; during this search the Transiting Planet Search algorithm performs 1E11 statistical tests. This is only possible with the high-performance computing available from the NAS facility. In addition, NAS visualization experts helped fine-tune the Kepler SOC software infrastructure and algorithms for use on Pleiades. The TESS mission will utilize NAS supercomputing capabilities for nearly all its computational needs to produce a new dataset every 27 days for use by the scientific community.