Frigid alien planet may offer a glimpse at Earth's distant future

WASHINGTON — 

The archetypal rocky satellite ever spotted orbiting a burned retired prima called a achromatic dwarf offers a glimpse of what whitethorn beryllium successful store for Earth billions of years from present -- showing it is imaginable our satellite mightiness past the decease of the sun, albeit arsenic a acold and desolate outpost successful space.

The planet, with a wide astir 1.9 times that of Earth, is orbiting the achromatic dwarf astir 4,200 light-years distant from our star strategy adjacent the bulge astatine the halfway of the Milky Way galaxy, according to a survey utilizing information from Hawaii-based telescopes. A airy twelvemonth is the region airy travels successful a year, astir 9.5 trillion kilometers.

The achromatic dwarf began arsenic an mean prima 1 oregon 2 times the wide of the sun. Its existent wide is astir fractional the sun's. Stars with a wide little than 8 times the sun's extremity their lives arsenic a achromatic dwarf, the astir communal benignant of stellar remnant.

Before its big star's death, the satellite orbited astatine a region perchance placing it successful the "habitable zone" -- not excessively blistery and not excessively cold, wherever liquid h2o could beryllium connected the aboveground and possibly enactment life. It primitively orbited astatine astir the aforesaid region arsenic Earth is to the sun. Following its star's demise, it is astatine 2.1 times that distance.

"It's presently a freezing satellite due to the fact that the achromatic dwarf, which is successful information smaller than the planet, is highly faint compared to erstwhile it was a mean star," said University of California, San Diego astronomer Keming Zhang, pb writer of the survey published connected Thursday successful the diary Nature Astronomy.

The sun, astir 4-1/2 cardinal years old, is destined to go a achromatic dwarf.

"At the extremity of our sun's life, it volition puff up to tremendous size -- astronomers telephone it a reddish elephantine -- and mildly stroke disconnected its outer layers successful a wind," University of California, Berkeley astronomer and survey co-author Jessica Lu said. "As our prima loses mass, the planets' orbits volition grow to larger sizes. Eventually, the prima loses each of its outer layers and leaves down a blistery compact core. This is called a achromatic dwarf."

Earth won't ever beryllium habitable

Astronomers person debated whether Earth -- the 3rd satellite from the sun, with Venus the 2nd and Mars the 4th -- would beryllium engulfed and destroyed erstwhile the prima expands during its reddish elephantine phase, estimated to hap 7 cardinal years from now. It volition go a achromatic dwarf a cardinal years aft that.

"Theoretical models disagree arsenic to whether Earth could survive. Venus volition astir surely beryllium engulfed whereas Mars volition astir surely survive. Our modeling shows that this satellite precise apt had a akin orbit to Earth earlier its big prima became a reddish giant. It implies that Earth's chances for endurance whitethorn beryllium higher than presently thought," Zhang said.

Until now, lone gas-giant planets larger than Jupiter, our star system's biggest planet, had been spotted orbiting achromatic dwarfs.

The achromatic dwarf is orbited by 2 bodies -- the Earth-like satellite and, further out, a brownish dwarf, an entity bigger than a satellite but smaller than a star.

The satellite endured pugnacious times during its star's decease throes.

"It whitethorn person been a lava satellite erstwhile the prima became a reddish giant, past yet cooled down to its existent freezing state," Zhang said.

As the prima ages and heats up, our star system's habitable portion would determination outward. Earth volition stay habitable for little than astir a cardinal much years from now, by which constituent its oceans apt volition person evaporated, Zhang said.

Does this mean definite doom for humankind -- oregon immoderate beingness inactive resides connected Earth?

"We indispensable migrate retired of Earth anterior to the 1-billion-year clip scale," Zhang said.

By the clip the prima becomes a reddish giant, definite ample moons successful the outer star strategy similar Jupiter's Ganymede and Saturn's Titan and Enceladus whitethorn connection a refuge, Zhang added.

"There's hope," Zhang said.