Searching for Other Earths

During six weeks every summer, for the past six years, University of California-Berkeley astrophysicist Geoff Marcy and five of his students have spent their nights in a small basement room on campus. The room has a microwave oven, a coffeemaker and a couch with two cushions. But none of them gets much use.

Each night, Marcy and his students – usually in teams of two – race to scour the skies from 11 pm until 9 am the next morning. Connecting remotely to one of the two Keck telescopes, in Hawaii, they search for planets outside our solar system, trillions of miles away. The Keck telescopes are some of the world's largest, and each night of looking at the stars with one of them costs $50,000.

“It’s a little embarrassing to describe how manic we are,” said Marcy. “From the time the sun sets till the moment when the sun rises, we don’t take any breaks. We just make sure the telescope is pointed at one star, and then immediately another star, and then immediately another star.”

On an early morning in August, Marcy and graduate student Lauren Weiss were doing just that, somewhat frantically making a last-minute decision to change the way they were taking measurements on a star called HTR248-002. By studying changes in starlight over time, astronomers are able to figure out if the star has any planets orbiting around it. This particular star has one Jupiter-size planet that has been confirmed. Marcy and Weiss were gathering data that could help them confirm the existence of a second planet, this one three times the mass of Jupiter.

The so-called exoplanets that Marcy and Weiss are looking for remained elusive for decades, until the first ones were discovered in 1995, first by a team in Switzerland, and shortly thereafter by graduate student Paul Butler and Marcy, who were then at San Francisco State University.

Discoveries of other planets outside our solar system exploded in 2009, when NASA launched the Kepler telescope into space, with the mission of finding planets in a constellation of our Milky Way galaxy. Kepler observed the slight dimming caused by planets as they crossed in front of their stars.

Based on Kepler’s observations, in 2013 Marcy’s student Erik Petigura, together with Marcy and Andrew Howard, of the University of Hawaii-Manoa, produced an estimate that revealed a stunning number of planets similar to Earth. Their calculations showed that in our galaxy roughly one out of five stars like the sun has an Earth-size planet at just the right distance from its star to potentially harbor water in liquid form.

“Forty billion Earth-size planets at habitable temperatures,” said Marcy. “And that’s just within our Milky Way galaxy.”

That estimate won Petigura, Howard and Marcy the 2013 National Academy of Sciences’ Cozzarelli Prize, a prestigious award that recognizes outstanding contributions to scientific research. Some 1,500 exoplanets have been confirmed, and another 3,400 exoplanets observed by Kepler await confirmation, according to exoplanets.org, run by Jason Wright, at Penn State.

Now, Marcy and his fellow astronomers are trying to figure out which Earth-size exoplanets might actually have water. With measurements from Kepler and Keck, they’re able to calculate a planet’s mass. The denser a planet is, the likelier it is to have a rocky surface where water could pool, allowing life to develop.

After four years of looking for Earth-size exoplanets, Kepler has suffered enough wear and tear that scientists can no longer use it to find Earth-size planets, said Marcy. The $600 million space telescope, which malfunctioned last year but was stabilized and renamed the K2 mission, is still able to look for exoplanets slightly larger than Earth. Marcy, Petigura and Howard are using it to figure out if exoplanets are as abundant in the rest of the Milky Way as they are in the constellation Cygnus that Kepler observed.

And the search for Earth-size exoplanets continues. A new telescope, the Automated Planet Finder, managed by the University of California-Santa Cruz, recently started collecting data at the Lick Observatory, in the hills east of San Jose. The APF gets its name from its ability to observe the skies without the presence of a human operator. With the Keck telescope and two other instruments, the HARPS-N telescope in the Canary Islands and the HARPS in Chile, the APF is one of a handful of powerful telescopes looking for Earth-size exoplanets that are much closer to Earth than the ones that Kepler observed.

Although considered nearby by astronomers, the closer planets would still take thousands of years for humans to reach with today’s fastest-known rockets. Yet they still intrigue scientists, offering tantalizing opportunities to look for signs of life.

“We can maybe look for the glinting of starlight off the oceans,” said Marcy. “Maybe we can analyze the light to look for chlorophyll, or the methane that would come from bovine flatulence or some such. So the nearest stars and their Earth-like planets represent some kind of an astro-biological goldmine, and we’re hunting for those Earths very vigorously.”

Update: On Oct. 14, 2015, Geoff Marcy resigned his professorship at UC Berkeley after an investigation found he violated campus sexual harassment policies.

This video was originally produced by Christopher Bauer and was updated by Gabriela Quirós.

Additional Links

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