Saturday, January 26, 2013

Searching for Nearby Earths

A complete census of planetary systems around Sun-like stars (FGK dwarfs) in the neighbourhood of the Sun out to a distance of 50 light years is highly desirable and will be a major milestone in the search for exoplanets. This can be achieved with a proposed mission called the Nearby Earth Astrometric Telescope (NEAT) which is sensitive enough to detect Earth-mass planets within the habitable zones of these nearby stars. NEAT is a space telescope that will carry out an astrometric survey of the 200 closest F, G and K-type stars in the Sun’s neighbourhood. Such an astrometric survey involves precisely measuring the position of a star and observing tiny changes in the star’s position caused by the presence of planets orbiting around the star. To accomplish this, NEAT performs extremely high precision astrometric measurements down to the 0.05 micro-arcsecond accuracy level.

The proposed mission architecture for NEAT consists of a pair of satellites flying in formation with one satellite being the telescope spacecraft and the other being the detector spacecraft. Both satellites are positioned precisely 40 metres apart since the telescope spacecraft consists of a one metre diameter parabolic mirror whose focal plane is located 40 metres away. The detector spacecraft will be at the focal plane where it will have ten 512 × 512 CCDs. Eight of the CCDs can be moved in the X and Y directions on the focal plane to image the reference stars while the central two CCDs are fixed in position - one CCD to image the target star and the other CCD to track the telescope’s axis. The use of 10 small CCDs instead of a billion-pixel focal plane dramatically reduces the mission cost.

Data obtained by NEAT will allow follow-up observations of planetary systems to be scheduled when the configuration of the planetary system is most favourable. In addition to detecting planets down to one Earth-mass around nearby stars, NEAT can also detect Jupiter-sized planets in long orbital periods around those planetary systems already discovered by the Kepler space telescope. Since the F, G and K-type stars in the Sun’s neighbourhood are all visible with unaided eyes or with simple binocular, the discovery of Earth-mass planets around these stars will dramatically change humanity’s view of the night sky.