The Search for Exosolar Systems

Abstract

There is currently a great interest in the discovery of exosolar systems, with the interest in eventually discovering planets in the habitable region about a star. This is the result of a series of questions popular today: Is our solar system unique? Are we alone? Are there a lot of planets out there? How do solar systems form? Are there planets in the habitable zone? Are there living organisms elsewhere? How does life begin? Is there intelligent life elsewhere? In the U.S. this is a part of the Origins program of NASA and has been, in part, the justification for maintaining the NASA budget. Space sciences in NASA is organized around four themes: Sun to Earth Connection, Planetary Exploration, Structure and Evolution of the Universe, and Origins of Life. Planetary search programs use different techniques. The radial velocity measurements can reach accuracies of 1–3m/s. Currently, by this technique planets have been discovered and these discoveries are biased by observational selection factors to periods less than 6 years and a mass limitation that cannot reach Earth sized planets. There are other possible detection methods that have the potential for discovering planets, such as astrometry using ground based observations by MAP, NPOI, Palomar Testbed, Keck Interferometer and speckle interferometry. Fourier Transform Spectrographs (FTS) offer the promise of reaching better accuracies in measuring radial velocities. Also direct imaging of planets by the Hubble Space Telescope (HST) is being attempted. There are large scale surveys such as the 2MASS infrared survey, DENIS, the Sloan Digital Sky Survey (SDSS), and the Schmidt plate surveys represented by the USNO A2.0 catalog. The astrometry is now sufficiently good, due to Hipparcos and Tycho-2, that these faint catalogs can be tied together to detect stars that have unusual spectra and thus, with accurate parallaxes, low mass stars can be detected.