Searching for, Finding, and Imaging Young Extrasolar Planets with HST/NICMOS

Imaging discovery and subsequent characterization of extrasolar planet (EP) mass companions to stars has been observationally challenging due to the severe planet-to-star contrast ratios. Since the detection of the extrasolar giant planet (EGP) companion to 51 Peg [1], continuing discoveries of 1 – 10 Jupiter mass companions by indirect methods have revealed an unanticipated diversity in mass ranges, dynamical properties, and primary-star characteristics. The past decade has seen an explosion of indirect detections of EGP companions to solar-like stars through radial velocity surveys [2] and more recently, in much smaller numbers, via photometric transits [e.g., 3], microlensing [4] and astrometry [5]. These methods are contributing enormously to this effort, and predicate the Kepler mission’s hopes of transitdetection of lower mass (i.e., terrestrial) planets. Yet, the direct detection of a bona fide EGP by imaging (and spectroscopy) remained elusive as recently developed technical capabilities (i.e., space-based with HST/NICMOS and complementary ground-based adaptive optics observations at longer-wavelength) were to be demonstrated. Today, young EGPs, still thermally emissive from their residual heat of formation can, and now have, been imaged in the near-IR at sub-arcsecond distances from their primaries using aggressive state-of-the art observing techniques such as differential coronagraphy with HST/NICMOS [6, 7] and AO augmented longer wavelength imaging at the largest ground-based telescopes [e.g., 8]. We illustrate with the very recently confirmed EGP image of 2M1207b. The observational parameter spaces enabled by these techniques probe for young Jovian mass planets at tens to hundreds of AUs from host stars within ~ 100 pc of the Earth. With the recent identification of very young (5 – 50 Myr) and “nearby” (< 70 pc) stellar associations [9], the hunt for EGPs using both space and ground based facilities is underway with vigor.