Differential Radial Velocity Spectrometer for extrasolar planetary studies

The large stellar/planetary flux ratio (>10⁶) and small angular separation (0.1 arcsec when observed from 10 parsecs) make it difficult to study Earthlike extrasolar planets. Hybrid coronographs with apodized masks and nulling by Earth based interferometric techniques could reduce the flux ratio by 3 orders of magnitude. Further reduction of starlight is possible with frequency filters. Due to large (upto 30 km/s) differences in radial velocities the specific spectral line for a particular molecule will be Doppler shifted by different amounts depending on from where, the star or the planet, the emission originates. The stellar spectrum itself could be used as a dynamic reference to determine the differential Doppler shift and define the frequency search space for the sought after planetary spectral line. The Differential Radial Velocity Spectrometer (DRVS) could use a heterodyne receiver with steep skirted filters and a laser local oscillator tracking the stellar spectrum. Several planetary spectral line windows should be searched and correlation/code gain techniques used to enhance detection capabilities.