TESS - Transiting Exoplanet Survey Satellite

TESS is NASA's next generation transit search mission. Like CHEOPS, TESS is going after the brightest stars in the sky. TESS will monitor roughly 2000 square degrees of the sky at any given time. For most of that field-of-view, the spacecraft will observe a select set of stars with a measurement of the stars’ brightness every minute for 27 days. Thus, TESS will be concentrating on the detection of short-period planets with orbits closer in than Mercury is to our Sun around the brightest 200,000 main-sequence stars over its two-year primary mission. Very small regions at the ecliptic poles will be visible in multiple TESS fields with observational baselines of 6 months to a year, enabling the search for planets in Earth-like orbits around solar-type stars. However, the vast majority of TESS discoveries will be short-period terrestrial and gas giant planets orbiting close to their parent stars.

TESS’s predecessor, the Kepler mission, has found a bounty of exoplanets, but most of the stars monitored in the prime Kepler mission were 12–14th magnitude. Unfortunately, these stars are too faint to obtain radial velocity measurements from the ground, even for those with giant planets. So, most of the planets discovered by Kepler do not have mass measurements. The aim of TESS is search the full sky for exoplanets around the very brightest stars, which will become candidates for further radial velocity study. This means a large sample of planets where we'll get their mean densities. This is incredibly exciting because we get to see what they're made of and how insolation from the parent star impacts their composition. In addition, we'll be able to compare their compositions to those for the best studied planets we know of: the planets residing in our own solar system.

TESS will also produce the first set of rocky planets around the brightest stars in the sky. These objects will be our best chance of getting densities of terrestrial planets outside the solar system. Radial velocity instruments push toward the cm/s resolution needed to spot the pull of an Earth-sized planet about the Sun. Currently, the best spectrographs can achieve 0.5–1 m/s resolution for the very brightest stars, but they’re pushing to increasing sensitivity toward obtaining mass measurements of rocky planets.

In addition to the science-grade data form TESS, there’s another really interesting component of the mission. The spacecraft will save an engineering frame of the entire ~2000 square degree field field of view every 30 minutes. These will also be downloaded and sent to Earth along with the light curves of the actual target stars. This is the same cadence as the original Kepler mission but 400 times more sky than Kepler ever covered! I fully expect that there will be a bonanza of interesting science and exoplanet discoveries to come out of mining those housekeeping/engineering frames from TESS in addition to their main science data. TESS is expected to launch in mid-2017.