In Search of Other Earths

Astronomers have spotted thousands of planets in orbit around distant stars over the last decade, and now what earthlings most want to know is whether any of them are similar to our own—and if they might harbor life.

To find out, NASA should develop a large “direct imaging” mission—namely, an advanced space telescope—capable of studying far-off planets, or exoplanets, orbiting stars similar to the sun, according to a new congressionally mandated report co-authored by Eliza Kempton, an assistant professor of astronomy.

While developing that capability will take a big investment and many years, the effort will help foster the scientific community and technological capability needed to answer fundamental questions about the universe, including what factors give rise to habitable, Earth-like planets.

“A big goal of the report was to make a roadmap for the next decade-plus, and we decided we didn’t want to step away from being very ambitious,” Kempton said. “A primary goal is to characterize planets that can and do bear life—a push toward finding the next Earth.”

That means having the ability to make detailed observations of exoplanets, and the authors recommended doing so using instruments to block the light emitted by parent stars. Currently, exoplanet discovery relies on indirect methods like observing movement of the star as a planet orbits it—known as the radial velocity method—or measuring changes in the light from a planet’s host star during the planet’s orbital cycle.

NASA’s planned Wide Field Infrared Survey Telescope (WFIRST), the large space-based mission that received the highest priority in the National Academies' 2010 survey, will be key to the discovery mission. Ground-based telescopes will also play a role in exoplanet discovery, the report said.

Kempton’s research uses theory to predict what astronomers should expect to observe from exoplanets with specific atmospheric compositions—especially those that are slightly larger than Earth, often referred to as super-Earths. In 2010, she  co-authored a paper in the journal Nature that described the first observation of a super-Earth atmosphere.

“I’ve been waiting my whole career to measure the composition of small planets’ atmospheres,” she said. “We’ll have those data very soon, so it’s a very exciting time.”