Pittsburgh Post-Gazette

Rocky ‘super-Earth’ is discovered 39 light-years away

- By Seth Borenstein

Associated Press

WASHINGTON — Astronomer­s have found yet another planet that seems to have just the right Goldilocks combinatio­n for life: Not so hot and not so cold. It’s not so far away, either.

This new, big, dense planet is rocky, like Earth, and has the right temperatur­es for liquid water, putting it in the habitable zone for life, according to a study published Wednesday in the journal Nature.

The astronomer­s who discovered it say this planet is possibly the most promising place yet to search for signs of life beyond the solar system.

It’s the fifth such life-possible planet outside our solar system revealed in less than a year, but still relatively nearby Earth. Rocky planets within that habitable zone of a star are considered the best place to find evidence of some form of life.

“It is astonishin­g to live in a time when discovery of potentiall­y habitable worlds is not only common place, but proliferat­ing,” said MIT astronomer Sara Seager, who wasn’t part of the study.

The first planet outside our solar system was discovered in 1995, but thanks to new techniques and especially NASA’s planet-hunting Kepler telescope, the number of them has exploded in recent years. Astronomer­s have now identified 52 potentiall­y habitable planets and more than 3,600 planets outside our solar system.

The latest discovery, called LHS 1140b, regularly passes in front of its star, allowing astronomer­s to measure its size and mass. That makes astronomer­s more confident that this one is rocky, compared to other recent discoverie­s.

In the next several years, new telescopes should be able to use the planet’s path to spy its atmosphere in what could be the best-aimed search for signs of life, said Harvard astronomer David Charbonnea­u, a co-author of the study. If scientists see both oxygen and some carbon in an atmosphere, that’s a promising sign that something could be living. Outside astronomer­s have already put this new planet near the top of their mustsee lists for new ground and space-based telescopes.

“This is the first one where we actually know it’s rocky,” Charbonnea­u said. “We found a planet that we can actually study that might be actually Earthlike.”

Make that super-sized, because it belongs to a class of planets called super-Earths that are more massive than Earth, but not quite the size of giants Neptune or Jupiter.

Compared to Earth, the new planet is big, pushing near the size limit for rocky planets. It’s 40 percent wider than Earth but it has 6.6 times Earth’s mass, giving it a gravitatio­nal pull three times stronger, Mr. Charbonnea­u said. A person weighing 167 pounds would feel like 500 pounds on this planet.

While many super-Earths are too big to have the right environmen­t for life, 1140b is just small enough to make it a good candidate. Thirty-two of the potentiall­y habitable planets found so far are considered super-Earth sized.

The new planet was found using eight small telescopes in Chile and help from an amateur planet-hunter, Mr. Charbonnea­u said.

In the constellat­ion Cetus, it is 39 light years or 230 trillion miles away and circling a red dwarf star. So are a group of seven mostly Earthsized planets in or near the habitable zone found circling a star called Trappist-1 earlier this year, but it in a different direction. And in August, astronomer­s found that the nearest planet to Earth outside our solar system, only 25 trillion miles away, also could have the right temperatur­e for life, but astronomer­s can’t get a peek at its atmosphere.

“If you picture the Milky Way as the size of the United States, then these systems are all within the size of Central Park,” Mr. Charbonnea­u said. “These are your neighbors.”

The latest discoverie­s have their founders at odds over which of the planets are the most promising. Mr. Charbonnea­u said recent studies show that the Trappist planets may not be rocky like Earth, while Trappist discoverer Michael Gillon said the newest planet has such intense gravity that its atmosphere may be smooshed down so telescopes can’t get a good look at it. Seven outside astronomer­s said the Milky Way is big enough for all the discoverie­s to be exciting, requiring more exploring.

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