EARTHLIKE PLANET DISCOVERED AROUND THE SUN'S CLOSEST NEIGHBOR

Astronomers have discovered an earthlike planet orbiting Proxima Centauri--the star closest to our sun. "It's the closest extra-terrestrial planet that will ever be found--there are no stars closer to Earth," says Guillem Anglada-Escude, at Queen Mary University of London, and one of the authors of the Nature article detailing the discovery.

Finding that our closest celestial neighbor harbors a small, rocky planet similar to Earth in the star's temperate zone suggests that potentially habitable earthlike planets are far from rare. Proxima Centauri is a red dwarf, smaller, cooler and less massive than the sun. M dwarfs like Proxima Centauri are the most abundant stars in the Milky Way Galaxy. Since M dwarfs live much longer than stars like our sun, life could have ample time to develop on their planets. "If only a small fraction of M dwarfs have temperate-zone planets, our Galaxy could be teeming with life," writes Artie Hatzes, an astronomer at the Thuringian State Obsevatory, in Germany.

Artist's impression of newly discovered exoplanet Proxima b, with Proxima Centauri and its companions, double star Proxima AB just above the horizon.
Credit: ESO/M. Kornmesser

The newly discovered planet circles Proxima Centauri well within the star's habitable zone--the so-called Goldilocks region that's neither too hot nor too cold for liquid water to exist on the planet's surface. The researchers calculate that Proxima b receives less heat from its star than Earth gets from the sun, but add that an atmosphere, if it has one, could boost its surface temperature enough to keep water from freezing or boiling away, just as Earth's atmosphere does for us.

Graphic showing that Proxima b orbits very close to its star, and within the star's habitable zone. Mercury's orbit around our sun is shown for comparison.
Credit: ESO/M.Kornmesser/G. Coleman

Although potentially habitable, Proxima B is by no means Earth's twin. It's at least 1.3 times as massive as Earth, its "year" is only 11.2 days long, and, like Mercury in our solar system, it's almost certainly tidally locked, with one side always facing its star. It's also blasted by far more high-energy particles and radiation than Earth, perhaps 100 times as much. Despite these differences, the researchers think a protective atmosphere could remain. "None of this excludes the existence of an atmosphere or of water," says Ansgar Reiners, an astrophysicist at the University of Gottingen.

Although astronomers saw the first hints of a planet around Proxima Centauri more than a decade ago, it took months of detailed observations by an international team using the state-of-the-art ESO telescopes in Chile earlier this year to confirm its existence beyond doubt. "When we combined the old and new data, the significance went sky high," says Anglada-Escude.

Researchers would love to learn more about Proxima b, starting with whether it does have an atmosphere and if so, what it's composed of. Another key question is whether the planet has a magnetic field like Earth's, strong enough to protect the atmosphere (and any life the planet might harbor) from stellar flares.

Although the planet is "just" 4.2 light-years away, it would take thousands of years to send a spacecraft to study it, using current technology. (Russian billionare Yuri Milner hopes to change that by using powerful laser blasts from Earth to boost smartphone-sized spacecraft to 20 percent of the speed of light. If his project, called Breakthrough Starshot, succeeds, it could speed a probe to Proxima Centauri in just 20 years).

Still, the star is close enough that the next generation of space telescopes could detect and analyze light from Proxima b and its atmosphere by blocking out light from the star. "We know the planet and its period," says Anglada-Escude. "So in the next months or years we can design an instrument to measure its properties. That will be a priority."

You can view an excellent video about the discovery, from Nature, at this URL.

Artist's impression of Proxima b orbiting reddish Proxima Centauri, with double star Proxima AB also visible. 

Credit: ESO/M. Kornmesser