Detection of Close-In Extrasolar Giant Planets Using the Fourier-Kelvin Stellar Interferometer

We evaluate the direct detection of extrasolar giant planets with a two-aperture nulling infrared interferometer, working at angles θ < λ/2B and using a new "ratio-of-two-wavelengths" technique. Simple arguments suggest that interferometric detection and characterization should be quite possible for planets much closer than the conventional inner working angle, or angular resolution limit. We show that the peak signal from a nulling infrared interferometer of baseline ≲40 m will often occur "inside the null" and that the signal variations from path difference fluctuations will cancel to first order in the ratio of two wavelengths. Using a new interferometer simulation code, we evaluate the detectability of all the known extrasolar planets as observed using this two-color method with the proposed Fourier-Kelvin Stellar Interferometer (FKSI). In its minimum configuration FKSI uses two 0.5 m apertures on a 12.5 m baseline and a ±20° field of regard. We predict that ~7 known extrasolar planets are directly detectable using FKSI, with low-resolution spectroscopy (R ~ 20) being possible in the most favorable cases. Spaceborne direct detection of extrasolar giant planets is possible with ~12 m baselines and does not require the much longer baselines provided by formation flying.