MRI Development: EXPRES - the Extreme Precision Spectrograph for Exoplanet Studies

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Extensive surveys over the past two decades using ground- and space-based observatories have cataloged thousands of planets beyond our solar system. Unfortunately, most discovery techniques are able to provide little more information than the orbital period around the parent star and the approximate surface temperature of the planet. Of vital interest is the planet's mass, since this, coupled with an estimate of its size, leads to a rough assessment of its composition (rocky or gaseous). Planetary masses are obtained through the gravitational attraction they exert on the parent star, with comparatively lightweight planets like the Earth providing only feeble influences on stellar motions. Indeed, the discovery of rocky, Earthlike exoplanets requires the development of techniques that can measure periodic motions of a star well below 1 meter per second, or approximately the speed of a person strolling down a sidewalk. Dr. D. Fischer (Yale University) seeks to accomplish exactly goal this by constructing an instrument especially for exoplanet study and using it on a new telescope high in the mountains outside Flagstaff, Arizona.The key to accurate radial velocity measurements of a star using the Doppler effect is stability: a stable temperature and pressure environment for the spectrograph, stable illumination of the instrument by the telescope, and a stable wavelength calibration source. Dr. Fischer's plan includes the construction of an instrument specifically designed for exoplanet study and its use on a telescope for a sizable, dedicated number of nights each year. The stability criteria will be met by enclosing the entire spectrograph in a temperature-controlled vacuum chamber, fiber-scrambling the input image, and calibration using a Fabry-Perot etalon source whose passband wavelengths are ultimately tied to an atomic clock with a stability of one part in 10^11. Using the instrument, Dr. Fischer expects to find and characterize as many as 100 Earth-like analogs orbiting nearby stars, and for the first time obtain reliable estimates of the frequency of possible life hosts beyond our solar system.Funding for the development of a precision instrument for the study of exoplanets is being provided by NSF's Division of Astronomical Sciences through its participation in the Major Research Instrumentation program and by the Office of Multidisciplinary Activities of the Directorate for Mathematical and Physical Sciences.