Astronomers have discovered at least two, and possibly three, planets orbiting a nearby star - a planetary system so close that a new generation of telescopes should be able to scrutinize it for potential chemical signatures of a living world, according to a report published Thursday in the journal Science.
The star is officially GJ 887, or Gliese 887, named for the scientist who put together a catalogue of stars. It's a red dwarf star - cooler than our sun and not nearly as big. It is 11 light-years away, or 64 trillion miles, which is cosmically right next door. Only 11 star systems are closer to our sun than this one.
Astronomers studied the light from the star for months and could see that it was being tugged by the gravity of orbiting bodies, according to the new report. The planets are outside our solar system - what astronomers call exoplanets.
"I would really like to go and explore," said Carole Haswell, an author of the paper and an exoplanet expert at Open University in London. "I would like to think that's where the human adventure is going."
At the simplest level, the discovery is the latest reminder that planets around stars are common - something no one knew just a generation ago, before the hunt for exoplanets took off in 1995, the year Swiss astronomers announced they'd detected a planet orbiting the star 51 Pegasi.
"Our dream is that every star has planets. It's becoming a reality," said Sara Seager, an astrophysicist at Massachusetts Institute of Technology who was not involved with this study. "It's incredible to see it come true."
Astronomers have found more than 4,000 exoplanets in recent decades. Scientists are eager to know whether these worlds have atmospheres - and, if so, what kind of gases envelop them. Water vapor, carbon dioxide and oxygen gas, in particular, may be markers of life on an alien world.
But many exoplanets are too far beyond the reach of atmosphere-sensing telescopes. Which is why this study is part of a project, run by the European Southern Observatory, focused on the closest stars. The team has so far found seven exoplanets around four stars.
"The newly detected planets orbiting Gliese 887 are the best possibilities, of all the known planets in close proximity to the sun, to see if they have atmospheres," said study author Sandra Jeffers, an astrophysicist at Germany's University of Göttingen.
Astrobiologists have long debated whether red dwarf stars are congenial to life. Most of them writhe with magnetic activity and erupt in flares, belching radiation potent enough to sterilize life. Yet GJ 887, the study authors observe, is remarkably calm. "This particular one presents a benign environment for its planets," Haswell said. "It's quite a nice one."
GJ 887 is the brightest red dwarf in the night sky but nonetheless is too dim to see with the naked eye.
What red dwarf stars lack in mass and brightness they make up in longevity. "Because they're burning their nuclear fuel so much more prudently, their life is very much longer" than suns like ours, Haswell said.
Jeffers, Haswell and an international team of astronomer colleagues used a planet-hunting telescope in the Chilean desert to monitor the star for three months. The device used in the study is so sensitive it can detect movements of a meter per second, Haswell said - it can sense a sun trillions of miles away, moving at speeds as slow as a person walks.
Subtle perturbations in the star's light revealed that gravity from nearby planets tugged on Gliese 887.
The pattern of those shifts of starlight suggested that two "superEarths" - at least four to seven times the size of our own - are orbiting the star at a close distance and at a dizzying rate, with one needing just nine days to complete a full tour and the other, 22 days.
Additional wobbles in the starlight hint at the existence of a third planet. "Whether there's more planets in the system, I don't know," said study author Paul Butler, an astrophysicist at the Carnegie Institution for Science.
The scientists could not say conclusively that they had found it because the star's natural activity might have created a false signal of a third orbiting body.
But if that planet is really there, it would be in the "habitable zone," an orbital region in which the amount of radiation from the star would allow water to remain liquid at the planet's surface rather than freezing or boiling away.