Transiting Exoplanet Survey Satellite

The Transiting Exoplanet Survey Satellite (TESS) is a planned space telescope for NASA's Explorers program, designed to search for exoplanets using the transit method.

The primary mission objective for TESS is to survey the brightest stars near the Earth for transiting exoplanets over a two-year period. The TESS project will use an array of wide-field cameras to perform an all-sky survey. With TESS, it will be possible to study the mass, size, density and orbit of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. TESS will provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future.

Previous sky surveys with ground-based telescopes have mainly detected giant exoplanets. In contrast, TESS will examine a large number of small planets around the very brightest stars in the sky. TESS will record the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.

Methods of detecting exoplanets

Any planet has an extremely faint light source compared to its parent star. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the extrasolar planets reported as of April 2014, have been observed directly, with even fewer being resolved from their host star.

Instead, astronomers have generally had to resort to indirect methods to detect extrasolar planets. At the present time, several different indirect methods have yielded success.

Established detection methods

The following methods have proved successful for discovering a new planet or detecting already discovered planet at least once:

Radial velocity

A star with a planet will move in its own small orbit in response to the planet's gravity. This leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth. The radial velocity can be deduced from the displacement in the parent star's spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet.