Science Summary

T

he Gemini Planet Imager (GPI) was built as a survey instrument to directly detect exoplanets and image debris disks. The direct measurements of exoplanets include the determination of their masses, compositions, orbital elements, and host star properties.

The indirect methods—Doppler, transit, and microlensing—are all powerful planet detection techniques, but direct imaging opens up a new discovery space. Imaging with a next-generation facility can probe from the “ice line,” where core accretion is likely most effective (5 AU), through the planetary migration zone, out to where disks are likely to be subject to instabilities that may form planets directly (50 AU). Doppler detection is too slow to probe this region; transits of wide- orbit planets are too rare and infrequent, and microlensing events detectable from the ground are rare and do not permit follow-up of planets. Moreover, direct imaging gives access to planetary atmospheric conditions, and can reveal dynamical interaction between dust and planets. Finally, imaging preferentially targets young (chromospherically active) stars inaccessible to other methods, allowing us to study planetary systems early in their evolution.

Composite image representing the close environment of Beta Pictoris as seen in the near-infrared light. The outer part of the image shows the reflected light on the dust disk observed in 1996 with the ADNIS instrument at ESO 3.6m telescope. The inner part is a 3.6 microns observation the the NACO AO system at the VLT. The newly detected source is a very young exoplanet.

Direct imaging of exoplanets has yielded some spectacular successes, such as the detection of Fomalhaut b with the Hubble Space Telescope, HR8799 system with the W.M. Keck 10m telescope, and Beta Pictoris b, a young exoplanet embedded in the dusty disk observed with the VLT 8m telescope. Those successes have been however achieved in isolation. Current facilities are almost exclusively sensitive to the youngest, most massive and widest-orbit planets. The successes likely represent rare objects, the extreme tail of some unknown distribution—telling us little about the underlying properties of Jovian planetary systems. Only through a large-scale, rigorously posed survey with a new-generation instrument can we obtain reliable statistical constraints.

Achieving this potential is the fundamental goal of the Gemini Planet Imager (GPI). GPI, a facility instrument for the Gemini South Observatory, will be the most sensitive planet imager ever constructed, an order of magnitude more powerful than current facilities and capable of discovering young (<1 GYr) planets from 5-100 AU.

HR 8799 exoplanetary system. Left: Inner portion of Keck NIRC2 K’ image from Marois et al. (2010a). Right: Simulated GPI H-band exposure of the system with an additional 3 M_J exoplanet inserted.