A few months ago, a team of Harvard astronomers that included Zachory Berta-Thompson ’07 made a thrilling discovery. Using remotely controlled telescopes in Chile, they observed a minute flicker of light from a star 39 light-years — or 234 trillion miles — away. That in itself wasn’t unusual, until they saw it again. “We saw a dip in the brightness of the star, and then we saw it repeat and repeat again every 1.6 days,” says Berta-Thompson, who now is a Torres Fellow in exoplanetary research at MIT.
That pattern represented the unmistakable orbit of a new planet, dubbed GJ 1132b, which may be astronomers’ best hope for understanding an extraterrestrial world. While astronomers have discovered more than 5,000 planets outside our solar system, which are known as exoplanets, the vast majority are hundreds or thousands of light-years away — much too far to examine in depth, never mind analyze for signs of life. But this new planet is within range of telescopes that can examine its features.
“Finding a rocky planet around a star in the Milky Way isn’t by itself particularly surpising,” says Berta-Thompson, who studied astrophysical sciences at Princeton before earning a Ph.D. at Harvard in 2013. “Those planets are extremely common. The thing that’s special about this one is that it’s especially easy to observe.”
Berta-Thompson is the lead author of a paper in Nature that reports that the planet is 1.2 times the size of Earth. By using massive telescopes to study the color of light that travels through the planet’s atmosphere as GJ 1132b passes in front of the star, the team hopes to find the fingerprints of molecules that can tell them about the planet’s atmosphere and geology — the first time those factors will be recorded for a rocky exoplanet. Due to its proximity to the star, one thing they don’t expect to find is any sign of life. “It’s quite a bit hotter even than Venus, so it’s probably lost all its water vapor to space,” Berta-Thompson says. “It’s impossible to imagine that any life could survive.”
Other planetary surveys have shown, however, that a star with one planet often has others as well. By using the powerful Spitzer Space Telescope, the team hopes to detect even tinier variations in the star’s light that could represent passage of another planet in the system. “It doesn’t have to orbit much farther away from its star to be cool enough to support life,” Berta-Thompson says. “That’s the planet we are optimistically hoping exists.”
Whether or not a cooler Earthlike planet exists in that far-off solar system, astronomers have much to learn just by studying GJ 1132b. Berta-Thompson makes a terrestrial analogy using his alma mater to explain the significance. “It’s like an entire library like Firestone, which has millions of books, but we’ll never be able to read them all,” he says. “This planet is like a book right in front of us on the shelf that we can take down and read.”