Scientists are keen to avoid the kind of infighting that took place during the 2010 decadal survey. NASA formed the Exoplanet Exploration Program Analysis Group (3) to referee and settle those kinds of disputes over data access and planning for future exoplanet missions. The group recently held a meeting in Seattle, Washington to take stock of what has been accomplished and what needs to happen next.
By any estimation, the Kepler has been a wildly successful mission. The telescope launched in 2009 and was placed in an Earth-following solar orbit. As of December 2014, it had confirmed the discovery of almost 1,000 exoplanets, ranging from super gas giants to a number of Earth-sized and super-Earth sized (rocky worlds larger than Earth that might still contain life.) Numerous other planet candidates are being evaluated.
The Kepler detected exoplanets by noting the decrease in brightness of stars when the planet orbited between the stars and the telescope. The amount of decrease derived what the diameter of the planet was and the period between the decreases derived the orbital period. Each candidate star system received follow-up observations by advanced ground-based telescopes to confirm the presence of one or more exoplanets.
The Future of Exoplanet Hunting
Looking to the future, scientists would like to use the upcoming James Webb Space Telescope (4) for exoplanet hunting. The JWST, due to launch in 2018, is designed for a wide variety of astronomical observations, mainly of stars and galaxies. The inclusion of a star shade that would blot out the light of a star would allow the JWST to directly image exoplanets up to 10 to 20 parsecs away from Earth.
However, scientists are keen to have a space telescope specifically dedicated to exoplanet hunting. The concept would involve placing a telescope at the L2 point where the gravity of the Earth and the moon cancel one another out. The L2 point lies beyond the moon from the Earth. Scientists would like the proposed telescope to be capable of being serviced by astronauts, similar to the Hubble Space Telescope. The servicing would likely be done by astronauts flying in an Orion spacecraft launched by the heavy-lift Space Launch System.
Scientists are also arguing over which sort of device would be used to block the light of a star in order to allow exoplanets to be directly imaged. One group favors a star shade similar to one being contemplated for the James Webb Space Telescope. Others prefer a coronagraph that would be installed inside the telescope. Budgets permitting; the new telescope might launch in the 2020s.
Finding New Worlds
In the meantime, NASA’s Wide-Field Infrared Survey Telescope (WFIRST)(5), due to launch in the mid-2020s, may have a coronagraph to allow it to detect the heat signatures of exoplanets.
The European Space Agency is planning the PLATO (Planetary Transits and Oscillations of stars) (6), which would detect exoplanets using Kepler’s indirect method, for 2024. NASA’s Transiting Exoplanet Survey Satellite (7), due to launch in 2017, will be able to hunt exoplanets orbiting half a million nearby stars.
The Holy Grail for exoplanet hunters remains the ability to directly image these new worlds. This capability will allow astronomers to analyze the content of the atmosphere of Earth-sized and super Earth-sized planets.
Those worlds that contain gasses such as nitrogen, oxygen, CO2, and water vapor would be prime candidates for containing life. The discovery of such a world, long imagined in science fiction, would profoundly change our understanding of our place in the universe and would enable the dreams of those who envision interstellar travel and the colonization of worlds warmed by other suns.