Space breakthrough
Planet found orbiting star nearest our solar system
Scientists announced on Wednesday the discovery of an Earth-sized planet orbiting the star nearest our sun, opening up the glittering prospect of a habitable world that may one day be explored by robots.
Named Proxima b, the planet is in a “temperate” zone compatible with the presence of liquid water — a key ingredient for life.
The finding, based on data collected over 16 years, was reported in the peer-reviewed journal Nature.
“We have finally succeeded in showing that a small-mass planet, most likely rocky, is orbiting the star closest to our solar system,” said co-author Julien Morin, an astrophysicist at the University of Montpellier in southern France.
“Proxima b would probably be the first exoplanet visited by a probe made by humans,” he told AFP.
An exoplanet is any planet outside our solar system.
Lead author Guillem Anglada-Escude, an astronomer at Queen Mary University London, described the find as the “experience of a lifetime”.
Working with European Southern Observatory telescopes in the north Chilean desert, his team used the so-called Doppler method to detect Proxima b and describe its properties.
The professional stargazers spent 60 consecutive days earlier this year looking for signs of gravitational pull on its host star, Proxima Centauri.
Regular shifts in the star’s light spectrum — repeating every 11.2 days — gave a tantalizing clue.
They revealed that the star alternately moved towards and away from our solar system at the pace of a leisurely stroll, about 5 kilometers per hour.
After cross-checking an inconclusive 2000-2014 dataset and eliminating other possible causes, the researchers determined that the tug of an orbiting planet was responsible for this tiny to-and-fro.
“Statistically, there is no doubt,” Anglada-Escude told journalists in a briefing.
“We have found a planet around Proxima Centauri.”
Proxima b is a mere four light years from the solar system, meaning that it is essentially in our backyard on the scale of our galaxy, the Milky Way.
It has a mass around 1.3 times that of Earth, and orbits about 7 million km from its star.
A planet so near to sun — 21 times closer than Earth — would be an unlivable whitehot ball of fire. But Proxima Centauri is a so-called red dwarf, meaning a star that burns at a lower temperature.
As a result, the newly discovered planet is in a “Goldilocks” sweet spot: neither so hot that water evaporates, nor so cold that it freezes solid.
But liquid water is not the only essential ingredient for the emergence of life.
An atmosphere is also required, and on that score the researchers are still in the dark. It all depends, they say, on how Proxima b evolved as a planet.
“You can come up with formation scenarios that end up with an Earth-like atmosphere, a Venus-like atmos- phere” — 96 percent carbon dioxide — “or no atmosphere at all,” said co-author Ansgar Reiners, an expert on “cold” stars at the University of Goettingen’s Institute of Astrophysics in Germany.
Computer models suggest the planet’s temperature, with an atmosphere, could be “in the range of minus 30 Celsius on the dark side, and 30C on the light side,” Reiners told journalists.
Like the moon in relation to Earth, Proxima b is “tidally locked,” with one face always exposed to its star and the oth- er perpetually in shadow.
Emerging life forms would also have to cope with ultraviolet and X-rays bombarding Proxima b 100 times more intensely than on Earth.
But even high doses of radiation do not preclude life, especially if we think outside the box, scientists say.
“We have to be very openminded as to what we call ‘life’,” Jean Schneider, an expert on exoplanets at the Observatoire de Paris, told AFP.
Liu Cixin, author of The Three-Body Problem and the first Asian to win the Hugo Award last year for best science fiction, told China Daily on Thursday he is aware of the news, but denied he is a prophet. “What I write is science fiction, but this is an astronomical discovery. They are unrelated,” he said. “I am not a prophet and I didn’t say it’s Centaurus in The ThreeBody Problem. I think people are just joking when they make the connection.”
We have to be very open-minded as to what we call ‘life’.” Jean Schneider, expert on exoplanets at the Observatoire de Paris