Boston astronomers have led recent discoveries of planets outside our solar system and are poised to begin searching for Earth-like ones.
Mason Inman
If you’ve ever wondered whether there’s life on other planets, Boston-area researchers can tell you how we could find out. As shown by two papers from Nature last week, local astronomers and astrophysicists are leaders in discovering and studying exoplanets—planets outside our solar system.
They have also become known for their work on transiting exoplanets—those that, as seen from Earth, pass in front of and behind their star. Focusing on this type of exoplanet is important for learning about whether these faraway systems can support life.
Researchers have found nearly all known exoplanets using the Doppler method, which detects shifts in the color of light coming from a star if it has planets orbiting it. But this method will only tell you the minimum mass of a planet and how long it takes to orbit its star.
To find out a planet’s actual mass, the composition of its atmosphere, and other features, researchers have to find and study transiting exoplanets. Because Boston researchers haven’t had much access to large ground telescopes, such as the W. M. Keck Observatory in Hawaii, they have had to rely on smaller telescopes. They’ve shown that you don’t need large telescopes to spot these elusive planets.
“If we wanted to get seriously into exoplanets, we had to find a niche for Harvard where we could be leaders,” says Dimitar Sasselov, professor of astronomy with the Harvard-Smithsonian Center for Astrophysics (CfA).
HD 189733b (artist’s conception), a recently discovered planet beyond our solar system, has been dubbed the “bull’s eye” planet because of the bright “hot spot” shown here. (Credit: David A. Aguilar, CfA)
Long-range view
As part of this effort, CfA researchers oversee HATNet and helped put together the Transatlantic Exoplanet Survey (TrES), two networks of small telescopes, similar in size to some used by amateur astronomers. These networks have found four transiting planets out of the 14 exoplanets discovered so far.
Researchers pinpoint a transiting planet as it passes in front of the star it orbits. Based on how much starlight the planet blocks, the researchers can determine the planet’s mass and density—crucial data for determining whether it might have rocks, oceans, or gas covering its surface.
Local researchers have also used the Hubble and Spitzer Space Telescopes to uncover more details about these planets, such as temperature and atmospheric conditions. These studies have led to a string of high-profile papers from Boston researchers in the last few years.
In a Nature paper published online last week, Sara Seager of MIT and colleagues used Spitzer to take the temperature of the hottest planet yet discovered—2,000 degrees Celsius. Heather Knutson and David Charbonneau of the CfA were coauthors of a paper in last week’s issue of Nature, reporting the first signs of weather on an exoplanet. They estimated that the Jupiter-like planet HD 189733b is home to winds that blast across its surface at four times the speed of sound.
Are we alone?
No one suspects that these particular planets harbor life. But the techniques and technology used to study these planets could, when further developed, help astronomers see if other Earth-like planets exist and, if so, whether they could support life.
Researchers are already thinking about how they might look for signs of life on these faraway planets. In a paper published earlier this year, Lisa Kaltenegger of the CfA described how astronomers could measure levels of oxygen, ozone, and other gases in the planets’ atmospheres.
NASA dealt a blow to the field last year when it delayed indefinitely the launch of two major planet-hunting space telescopes, Terrestrial Planet Finder and SIM PlanetQuest, as it shifted focus towards lunar and Mars exploration. These telescopes would have searched for Earth-like planets and signs of life.
”A lot of people are frustrated about it,” says Josh Winn, an astrophysicist at MIT, who, along with Seager, sits on NASA’s Exoplanet Task Force.
But Winn remains optimistic about the future of the field with existing equipment. “There’s been a lot of progress with transiting planets, squeezing as much information from those systems as possible, which wasn’t anticipated.”