Another Earth could be circling the star right next door to us.
Astronomers announced Wednesday that they had detected a planet orbiting Proxima Centauri, the closest neighbor to our solar system. Intriguingly, the planet is in the star’s “Goldilocks zone,” where it may not be too hot nor too cold. That means liquid water could exist at the surface, raising the possibility for life.
Although observations in recent years, particularly by NASA’s Kepler planet-finding mission, have uncovered a bounty of Earth-size worlds throughout the galaxy, this one holds particular promise because it might someday, decades from now, be possible to reach. It’s 4.2 light-years, or 25 trillion miles, away from Earth, which is extremely close in cosmic terms.
One astronomer likened it to a flashing neon sign.
“I’m the nearest star, and I have a potentially habitable planet!” said R. Paul Butler, an astronomer at the Carnegie Institution for Science and a member of the team that made the discovery.
Guillem Anglada-Escudé, an astronomer at Queen Mary University of London and the leader of the team that made the discovery reported in the journal Nature, said, “We know there are terrestrial planets around many stars, and we kind of expected the nearby stars would contain terrestrial planets. This is not exciting because of this. The excitement is because it is the nearest one.”
Beyond the planet’s size and distance from its parent star, much about it is still mysterious. Scientists are working off computer models that offer mere hints of what’s possible: Conditions could be Earthlike, but they could also be hellish like Venus, or cold and dry like Mars.
There is no picture of the planet, which has been designated Proxima b. Instead, Anglada-Escudé and his colleagues detected it indirectly, studying via telescope the light of the parent star. They zeroed in on clocklike wobbles in the starlight, as the colors shifted slightly to the reddish end of the spectrum, then slightly bluish. The oscillations, caused by the bobbing back-and-forth motion of the star as it is pulled around by the gravity of the planet, are similar to how the pitch of a police siren rises or falls depending on whether the patrol car is traveling toward or away from the listener.
From the size of the wobbles, the astronomers determined that Proxima b is at least 1.3 times the mass of Earth, although it could be several times larger. A year on Proxima b — the time to complete one orbit around the star — lasts just 11.2 days.
Although the planet, lost in the glare of the star, cannot be viewed by current telescopes, astronomers hope to see it when the next generation is built a decade from now.
And the planet’s proximity to Earth gives hope that robotic probes could someday be zooming past the planet for a close-up look. A privately funded team of scientists and technology titans, led by the Russian entrepreneur Yuri Milner and the theoretical physicist Stephen Hawking, have announced Breakthrough Starshot Initiative, a project to develop and launch a fleet of iPhone-size spacecraft within two to three decades. Their proposed destination is the Alpha Centauri star system, which includes two larger sunlike stars in addition to Proxima Centauri.
“We will definitely aim at Proxima,” said Avi Loeb, a Harvard astronomer who is chairman of an advisory committee for Breakthrough Starshot. “This is like finding prime real estate in our neighborhood.”
This newly discovered planet is much closer to its parent star, about 5 million miles apart, than Earth is to the sun, 93 million miles. Even Mercury, the innermost planet of our solar system, is 36 million miles from the sun.
While Proxima b might be similar to Earth, its parent star, Proxima Centauri, is very different from the sun. It is tiny, belonging to a class of stars known as red dwarfs, with only about 12 percent of the mass of the sun and about 1/600th the luminosity — so dim that it cannot be seen from Earth with the naked eye.
Thus Proxima b, despite its closeness to the star, receives less warmth than Earth, but enough that water could flow on the surface. Whether the planet has liquid water or an atmosphere is “pure speculation at this point,” Anglada-Escudé said in a news conference.
© 2016 The New York Times Company
