Searching for life with giant telescopes

The Kepler Space Telescope discovered more than 2,600 exoplanets—planets orbiting stars other than our Sun. Kepler used the transit method, watching for tiny dips in the amount of light coming from a star when a planet passed in front of it. After more than nine years in space, Kepler ran out of fuel last month and NASA officially ended the telescope’s science mission. The torch has been passed to a new generation of planet hunters, and experts in the field of exoplanets say we may be less than a decade away from answering one of humanity’s biggest questions: is there life somewhere besides Earth?

Harvard physics Prof. David Charbonneau
gave a lecture at the UW Oct. 16.
Photo: Greg Scheiderer.

“We are the special generation that for the first time in human history is going to have the technological ability—if we choose—to go and answer this great question,” said David Charbonneau, professor of astronomy at Harvard University and a member of the Kepler mission team. Charbonneau gave a lecture recently at the University of Washington, part of the Frontiers of Physics series. He suggests that when we look for an inhabited planet, we don’t confine ourselves to just finding people.

“There may be other humans out there, but I’m going to advocate that we need to create and cast the broadest net possible when we go and actually make the first search for life outside the solar system,” Charbonneau said. He noted that SETI has been listening for years with no contact so far, and other planets are too far away to visit any time soon. But we are on the verge of being able to analyze the chemical content of exoplanet atmospheres, and that can tell us if there’s life on the ground. A scientist on a distant planet looking at Earth could tell there is life here by the chemicals in our atmosphere.

“Life has radically changed the content of our atmosphere,” he said, by creating oxygen and other elements. “We’re going to try to detect life through the unintentional waste products that are produced as life goes about its business.”

News reports of discoveries often note if an exoplanet is “Earth-like,” but in reality we know little about conditions on these far-away worlds. We can accurately figure an exoplanet’s size, mass, and density, but know little else about them. Two new telescopes—one in space, one on the ground—may be able to give us the data we need to know about actual conditions on these planets.

Giant Magellan Telescope

The Giant Magellan Telescope (GMT) is being built in Chile by an international consortium, and is expected to begin science operations around 2023. The GMT will be the largest optical telescope ever constructed, with seven 8.5-meter mirrors. This huge telescope will be able to gather an enormous amount of light, enough to analyze the atmospheres of exoplanets.

James Webb Space Telescope

The James Webb Space Telescope (JWST) is a NASA project scheduled to launch in 2021. JWST will have a 6.5-meter primary mirror, and the observatory will be able to observe light in the infrared, and that’s important.

“Infrared is where all the molecules we want to study show their fingerprints,” Charbonneau said, listing oxygen, water, and methane among the molecules of interest.

He said the JWST “will revolutionize essentially all major branches of astrophysics.”

Charbonneau said we need both of the new telescopes to nail down whether an exoplanet is inhabited.

“Individually, a large ground-based telescope or the James Webb Space Telescope cannot tell us if there’s life on a planet,” he said. That’s because they’re sensitive to different molecules. The GMT could spot oxygen, which usually means life. It’s not certain, though, because oxygen could be created in other ways. The JWST could find methane, carbon monoxide, and carbon dioxide, which would put that oxygen in context, determining if it’s there because of biological activity.

“The idea is together they can get the data that will allow us to conclude that there really is life,” Charbonneau said.

TESS and MEarth

While we wait for these two observatories to be completed, astronomers are not sitting idly by. NASA’s Transiting Exoplanet Survey Satellite (TESS) is continuing the work of Kepler, using the transit method to search for more exoplanets.

“Our mission is to find hundreds of nearby small planets amenable to detailed characterization,” said Charbonneau, who is a co-investigator on the mission. TESS will survey the entire sky over a period of two years. It was launched in April, began science work in August, and found its first exoplanet in September. Charbonneau said that by December they should have the data to determine if this new exoplanet has an atmosphere.

Charbonneau is the primary investigator for the MEarth Project, which is searching for habitable exoplanets around nearby stars. MEarth consists of two automated observatories, one near Tucson, Arizona and the other in Chile. Each employs eight robotic 16-inch telescopes that constantly watch M-dwarf stars for transiting exoplanets. There are several good reasons to look at these “red dwarf” stars. They’re plentiful—there are about 240 of them within 30 light years of us, compared to just 20 G-stars like the Sun. Since they’re smaller stars and not as bright, they won’t wash out an orbiting planet’s atmosphere, making the observation technically easier.

The following time-lapse video shows the MEarth-North observatory in action.

The point of both TESS and MEarth is to create a good list of things for GMT and JWST to check out once they come on line.

“The search for atmospheric biomarkers such as oxygen will be humanity’s first attempt to really answer this great question about whether or not we are alone,” Charbonneau said.

You can watch the entire lecture here: