2017-11-15 06:52:03
Eleven Light-Years Away, an Earth-Size Planet That May Be Habitable

06:52, November 15 43 0

There’s a new place to look for life in the universe.

Astronomers announced on Wednesday the discovery of an Earth-size planet around a small red star in our corner of the galaxy. The planet could hold liquid water and conditions favorable for life.

The star, Ross 128, is not the closest with a planet similar in size to ours. That would be the sun’s next door neighbor, Proxima Centauri, just 4.2 light-years away.

And there appears to be just one planet orbiting Ross 128 — not the bounty of seven Earth-size planets that circle Trappist-1, a red dwarf about 40 light-years from here.

But unlike those stars, Ross 128, about 11 light-years from Earth, appears to be a quiet, well-behaved star, without the violent eruptions of radiation that might wipe out any beginnings of life before they had a chance to take hold on the planet.

“Those flares can sterilize the atmosphere of the planet,” said Xavier Bonfils of the Institute of Planetology and Astrophysics in Grenoble, France, the lead author of a paper describing the planet. “Ross 128 is one of the quietest stars of the neighborhood.”

The findings appear in the journal Astronomy and Astrophysics.

The astronomers did not directly see the planet but instead used a telescope in Chile to measure wobbles in the wavelengths of light coming from the star. The wobbles are caused by the gravitational pull of the unseen planet.

The magnitude of the wobbles indicates that the planet is at least 1.35 times the mass of Earth but could easily be twice the mass of Earth.

Astronomers’ instruments are not yet sensitive enough to spot Earth-size planets in Earthlike orbits around stars similar to our sun. It is easier to detect Earth-size planets around dimmer and cooler stars known as red dwarfs, which are the most common type of star in the Milky Way.

Astronomers have in the past couple of decades discovered an abundance of star-hugging planets, far different from anything in our solar system. The Ross 128 planet is only about 4.5 million miles from the star, much closer than the 93 million miles between Earth and the sun. Even Mercury, the innermost planet of the solar system, is 36 million miles from the sun.

If the newly discovered planet were the same distance from the red dwarf as Earth is from the sun, it would be frigid. But it is close enough to Ross 128 that it absorbs warmth sufficient for liquid water, one of the requisite ingredients for life, to potentially exist on the surface. (If anything, the planet may be too warm, more like the planet Venus.)

Dr. Bonfils said Ross 128 appears to be at least 5 billion years old — older than our solar system — and perhaps as old as 10 billion years. The star may have been more turbulent in its youth. But even if solar flares billions of years ago stripped away the planet’s atmosphere, it could have been replenished by gases emanating from the planet’s interior, Dr. Bonfils said.

Vladimir Airapetian, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md., questioned whether Ross 128 would be such a benign star.

“Even being quiet, its X-ray to extreme U.V. emission can be 10 times higher than that of the sun,” said Dr. Airapetian. That amount of radiation might be enough to destroy the planet’s atmosphere.

In an Astrophysical Journal Letters article in February, he and his colleagues noted that radiation from red dwarf stars might strip oxygen from the atmospheres of nearby planets.

William C. Danchi, also a Goddard astrophysicist and an author of that article, was more positive.

“There is potential for an atmosphere and hence habitability, but it is highly uncertain,” he said. “This is an important discovery and well worth many follow-up studies.”

The next generation of large terrestrial telescopes, with mirrors 100 feet or more in diameter, should be able to make out the planet circling Ross 128 and possibly identify specific molecules in its atmosphere.

“It would be rather easy to search for oxygen in the atmosphere of such a planet,” Dr. Bonfils said.