“Is the solar system a cosmic rarity or a galactic commonplace? How do Earth-like planets form, and what determines whether they are habitable? Is there life on other worlds?”
These questions were asked by a committee of prominent exoplanet researchers who recently compiled a report recommending a 20-year strategy for the study of distant worlds. The report was initially released by the National Academies of Sciences, Engineering, and Medicine in September and was published in its final form earlier this week.
The committee outlined two overarching goals of exoplanet science: first, to understand the formation, evolution, and diversity of planets and planetary systems and, second, to identify potentially habitable worlds, learn how common they are, and search for distant life.
“The past decade has delivered remarkable discoveries in the study of exoplanets,” the committee wrote. To keep that momentum going, it made seven strategic recommendations for NASA and other funding agencies to meet these goals in the next 20 years:
- A space-based mission is needed that can directly image the light reflected from planets and measure their spectra. These measurements would reveal clues about a planet’s atmospheric composition and temperature and detect planets that are not observable through other methods. Such a mission should be designed specifically to image small and temperate planets around Sun-like stars.
- Ground-based giant segmented mirror telescopes, like the future Giant Magellan Telescope and the Thirty Meter Telescope, will be key for the U.S. exoplanet community. Combined, the telescopes’ exoplanet-specific instruments will be capable of observing the whole sky and should be high priorities for U.S. investment.
- NASA’s Wide Field Infrared Survey Telescope (WFIRST), a space telescope, will be able to observe exoplanets different from any seen by previous missions and needs to be launched. WFIRST’s gravitational microlensing instrument will observe massive planets in distant orbits, as well as free-floating planets not bound to stars. The telescope’s coronagraph will measure the spectra of hot and still-forming planets.
- Measuring the mass of an exoplanet is essential to learning what it is made of, so NASA should help develop extremely precise radial velocity (EPRV) instruments. “If scientists seek to study Earth-like planets orbiting Sun-like stars, they need to push mass measurements to the sensitivity required for such worlds,” the report says. Current radial velocity instruments, which detect the mass of a planet through its gravitational influence on the host star, are not precise enough for this task.
- The James Webb Space Telescope (JWST), currently scheduled to be launched in 2021, should conduct a systematic survey of the atmospheres of exoplanets. Astronomers could combine an exoatmosphere survey with size measurements from the Transiting Exoplanet Survey Satellite and the now-retired Kepler and mass measurements from future EPRV instruments. This would let them fully characterize thousands of planets and begin to learn how common Earth-like planets really are.
- “The identification of life on an exoplanet will not be accomplished by a single team of researchers, nor by a single method,” the report states. NASA should support the development of a cross-disciplinary exoplanet research network that will coordinate complementary projects that bridge scientific fields.
- Agencies need to robustly fund individual investigator grants in theoretical and laboratory astrophysics, experimental physics and chemistry, solar astronomy, and other related fields. Knowledge of an exoplanet is only as good as the understanding of its host star and the underlying physical processes, the report argues, so large exoplanet missions must be supported by the most up-to-date foundational science.
The report recommends that the next 5 years be devoted to JWST, individual investigator grants, and interdisciplinary and workforce development. The following 10 years should focus on WFIRST, the large ground-based telescopes, and precision radial velocity. Last, planning for a space-based direct imaging mission should begin soon, the team said, with a target completion date of 20 years from now.
“For generations, humans have looked up at the stars and wondered whether we are alone,” the team wrote. “What we do know is that we can be the first with the technological and scientific ability to answer the question, if we so choose.”
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer