On high-contrast characterization of nearby, short-period exoplanets with giant segmented-mirror telescopes

Max-Planck Institüt für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: ianc@mpia.de

Received: 14 December 2012
Accepted: 21 January 2013

Abstract

Measurements of the frequency with which short-period planets occur around main sequence stars allows a direct prediction of the number and types of such planets that will be amenable to characterization by high-contrast instruments on future giant segmented-mirror telescopes (GSMTs). Adopting conservative assumptions, I predict of order 10 planets with radii R_P = 1−8 R_⊕ and equilibrium temperatures  ≲400 K should be accessible around stars within 8 pc of the Sun. These numbers are roughly the same for both near-infrared observations of scattered starlight and mid-infrared observations of planetary thermal emission, with the latter observations demonstrating greater relative sensitivity to smaller and cooler planets. Adopting the conservative assumption that planets with R_P = 1−2 R_⊕ and 2−4 R_⊕ occur with equal frequency, I predict a 40% chance that a planet with R_P = 1−2 R_⊕ and equilibrium temperature 200–250 K will accessible to high-contrast thermal infrared characterization; this would be a compelling object for further study. To validate these predictions, more detailed analyses are needed of the occurrence frequencies of low-mass planets around M dwarfs, both in the Kepler field and in the solar neighborhood. Several planets already discovered by radial velocity surveys will be accessible to near-infrared high-contrast GSMT observations, including the low-mass planets α Cen Bb and (depending on their albedos) GJ 139c and d, GJ 876b and c, and τ Cet b, c, and d; τ Cet f would be amenable to thermal infrared characterization. Further efforts to model the near-infrared reflectance and mid-infrared emission of these and other short-period planets are clearly warranted, and will pave the way for the interpretation of future high-contrast characterization of a variety of planets around the nearest stars.