The first direct measurement of a super-Earth exoplanet’s atmosphere finds the world is either shrouded in steam or covered in clouds.
“This is the first probe of an atmosphere of a super-Earth planet,” said exoplanet observer Jacob Bean of the Harvard-Smithsonian Center for Astrophysics, lead author of a paper describing the cloudy world in the Dec. 2 Nature. “It’s a real big step in the direction of doing this kind of work for a planet that’s potentially habitable.”
The planet, called GJ 1214b, is the smallest planet yet to have its atmosphere examined — but it’s just the latest in nearly a decade of probing exoplanet atmospheres. The others have all been gas giants.
When the first exoplanet atmosphere was measured in 2002, many astronomers dismissed it as a one-time success. Now, just 8 years later, exo-atmosphere studies are a thriving field.
Astronomers hope eventually to find true twins of Earth: small rocky planets with liquid water and atmospheres that could support life. Teasing out which molecules make up exo-atmospheres will be crucial to that search.
“Ultimately the goal is to try to look for biosignatures,” Bean said. “This work is another sort of milestone on this road. We’re going directly towards that.”
This gallery traces the history of the study of exoplanet atmospheres, and looks forward to how astronomers plan to search for the real exo-Earth.
This planet was hailed as the most Earth-like exoplanet yet when announced almost exactly a year ago. It was only the second super-Earth — a planet with a mass between about 2 and 10 times Earth’s — found to pass in front of its star, or transit.
The amount of light the planet blocked as it eclipsed its star told astronomers how big the planet was, about 2.7 times as wide as Earth. Follow-up measurements of the planet’s gravitational tug on the star showed it was 6.5 times Earth’s mass. Taken together, these two numbers tantalizingly suggested the planet could be one big, hot ocean world. But it could also be a kind of mini-Neptune, with a solid core and an atmosphere of hydrogen and helium, or a rocky planet with a huge atmosphere made of hydrogen.
The first system of planets to have its portrait taken orbits the star HR 8799, captured by ground-based telescopes in Hawaii and California in 2008.
Future prospects for finding Earth twins could involve placing a giant, flower-shaped shield in front of a space telescope to block starlight, like the proposed New Worlds Observer.