Photochemistry of Terrestrial Exoplanet Atmospheres - Planetary Exploration and Science: Recent Results and Advances - page 298

Full-sky surveys intended to discover terrestrial exoplanets around nearby main-
sequence stars are being planned. The survey of terrestrial exoplanets around nearby
systems is far from complete in several important areas: (1) Earth-mass planets
around FGK stars have just become in the reach of the radial velocity method
(Dumusque et al. 2012 ); (2) precise spectroscopic and photometric measurements
of M dwarfs, despite their dominant numbers in our interstellar neighborhood,
have been long impeded by the faintness of these stars and the concentration
of their radiation in the near-infrared wavelengths that are strongly contaminated
by Earth's atmosphere (Nutzman and Charbonneau 2008 ); (3) Kepler , although
sensitive to Earth-sized planets, targets a small patch of sky and focuses on faint
stars to maximize its scientific return (Batalha et al. 2010 ). One could expect
rapid developments in all these areas. In particular, an all-sky space-based TESS
mission (Transiting Exoplanet Survey Satellite) has recently been selected by
NASA for launch in 2017 (Ricker et al. 2010 ). And the CHaracterising ExOPlanet
Satellite (CHEOPS) and the PLAnetary Transits and Oscillations of stars (PLATO),
also designed to search for terrestrial exoplanets around nearby bright stars, have
been selected by European Space Agency (ESA) for launch in the next decade
(Broeg et al. 2013 ; Rauer et al. 2013 ). One could expect a rapid growth in the
number of terrestrial exoplanets that are suitable for follow-up observations of their
atmospheres in the coming years.
The next-generation observation facility will allow thick atmospheres to be
observed in great detail and even allow characterization of thin atmospheres
on terrestrial exoplanets around late-type stars. Today's studies on hot Jupiter's
atmospheres are flourishing with the Hubble Space Telescope and the Spitzer Space
Telescope (see Seager and Deming 2010 and references therein), but much detection
of atmospheric molecules remains controversial (Deming et al. 2013 ). In 5-10
years, larger and more sophisticated facilities will allow measurements of molecular
abundances and characterization of atmospheric chemistry in thick atmospheres of
gas giants, and super-Earths around M dwarf stars, to great detail (Traub et al. 2008 ;
Kaltenegger and Traub 2009 ;Beluetal. 2011 ). These anticipated facilities include
the James Webb Space Telescope (JWST) slated for launch in 2018 (Gardner et al.
2006 ), and the giant 20- to 40-m class ground-based telescopes that include the
Extremely Large Telescope (Gilmozzi and Spyromilio 2008 ), the Giant Magellan
Telescope (Johns et al. 2012 ), and the Thirty Meter Telescope (Crampton and
Simard 2006 ).
In the more distant future, the community still holds hope that a direct-imaging
space-based mission under the Terrestrial Planet Finder concept (e.g., Traub et al.
2006 ; Beichman et al. 2006 ; Levine et al. 2009 ) will enable Earth-like terrestrial
exoplanets to be characterized. The technique of exoplanet direct imaging has been
advancing rapidly and proceeding into spectroscopic observations of giant planets
(Konopacky et al. 2013 ). A number of coronagraph instruments are mounted on
state-of-the-art 10-m class telescopes, which will enable spectroscopic studies of
extrasolar gas giants (e.g., Gemini Planet Imager, Chilcote et al. 2012 ). Notably,