The Fourier-Kelvin Stellar Interferometer: Exploring Exoplanetary Systems with an Infrared Probe-class Mission

We report results of a recent engineering study of an enhanced version of the Fourier-Kelvin Stellar Interferometer (FKSI) that includes 1-m diameter primary mirrors, a 20-m baseline, a sun shield with a ±45◦ Fieldof-Regard (FoR), and 40K operating temperature. The enhanced FKSI is a two-element nulling interferometer operating in the mid-infrared (e.g. ∼ 5-15 μm) designed to measure exozodiacal debris disks around nearby stars with a sensitivity better than one solar system zodi (SSZ) and to characterize the atmospheres of a large sample of known exoplanets. The modifications to the original FKSI design also allows observations of the atmospheres of many superEarths and a few Earth twins using a combination of spatial modulation and spectral analysis. 1. Design Evolution of FKSI During the last few years, considerable effort has been directed towards flagshipscale missions to detect and characterize Earth-radius down to Mars-radius planets around nearby stars in the mid-infrared (∼ 7− 20 μm), namely the Darwin and Terrestrial Planet Finder Interferometer (TPF-I) missions. However, cost and technological issues such as formation flying and control of systematic noise sources are likely to prevent these missions from entering Phase A until the 2020+ time frame. Presently more than 400 exoplanets have been discovered, and little is known about the majority of them other than their approximate mass, semi-major axes, and eccentricities. FKSI was originally conceived of as a Discovery-class mission for an imaging and nulling interferometer for the nearto mid-infrared spectral region (3 – 8 μm) (Danchi et al. 2003; Barry et al. 2006; Danchi & Lopez 2007), with a 12.5 m baseline, cooled to 65K, and with an FoR of ±20 degrees. The shorter wavelength operation allowed for a reduction in costs primarily through simpli-