Astronomers find first Earth-sized rocky planet


No one is going to be living there — or even visiting — but astronomers using the W.M. Keck Observatory have found the first rocky, Earth-sized planet.

The planet, Kepler-78b, isn’t in what scientists call the Goldilocks zone, the proximity from a star — not too close and not too far — that could sustain life. Kepler-78b isn’t just outside of that zone, either. It’s so close to its host star that an orbit takes a mere 8.5 hours and its temperature is more than 2,000 degrees.

Keck was particularly instrumental in getting the exact measurements needed to calculate the planet’s density, Howard said.

“The density is the same as Earth,” he said. “That means it is probably made of the same stuff as Earth.”

Why is that particularly noteworthy? Howard said since scientists discovered the first exoplanet 20 years ago, they have found plenty of planets Earth-sized or slightly larger, but none that are rocky.

“Within our solar system, we see a few different planet types,” Howard said. “With the history of exosolar planets, it’s been a story of continual surprises, densities and orbits we didn’t expect.”

Despite finding that variety of planets, but no rocky planets like Earth, scientists were beginning to wonder if Earth was an unduplicated oddity.

“At least (Kepler-78b) shows that nature can do it outside the solar system,” Howard said.

Howard and his team used data collected by NASA’s Kepler telescope, combined with eight nights of Keck I observations. While they were working on their observations and calculations, a second team, led by a Swiss astronomer, used the same Kepler data and independent telescope observations to study Kepler-78b.

“We basically confirmed each other,” Howard said, adding it was unusual for two separate teams to tackle the same question and agree to publish their papers at the same time without discussing their data or findings. Also unusual, he said, was for one journal to agree to simultaneously publish the resulting academic papers. “I breathed a huge sigh of relief when we agreed.”

The papers were published this week in the journal Nature.

Howard said he would like to learn more about Kepler-78b. The planet’s presence proves more planets exist with Earth’s size and density.

“It’s hard to imagine how it formed,” Howard said, noting one of the big questions the discovery raised.

Keck Director Taft Armandroff said Keck officials were thrilled to play a role in the discovery.

“It shows we can find things that are this size and mass,” Armandroff said. “It will only be a matter of time until we find one in the Goldilocks zone.”

Other team members included Massachusetts Institute of Technology’s Roberto Sanchis-Ojeda, who analyzed the transit data taken by the Kepler spacecraft to find the planet and calculate its size, Geoffrey Marcy from the University of California, Berkeley, John Johnson from Harvard University, Debra Fischer from Yale, UH-Manoa graduate students Benjamin Fulton and Evan Sinukoff and Jonathan Fortney from the University of California, Santa Cruz.