A small star only 11 light-years from our solar system may play host to a clutch of planets, one of which might be suitable for life.
The astronomers observed the red dwarf using HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph the European Southern Observatory in Chile.
The worldwide "RedDots" team - joined by Australian astronomers at UNSW Sydney, Macquarie University and University of Southern Queensland for this work - has detected a system of super-Earth planets orbiting the brightest red dwarf star in the sky, Gliese 887. For those who do not know, super Earth is planets that have a higher mass than Earth but are much less than Neptune and Uranus.
But stars like these are cooler than the Sun, which means the habitable zone - the orbital band where temperatures are mild enough to allow liquid surface water - is much closer to GJ 887 in comparison with the Earth's distance from the Sun.
"We used a technique known as Doppler wobble, which enables us to measure the tiny back and forth wobbles of the star caused by the gravitational pull of the planets", they explained. Now, researchers say they've spotted a nearby star that appears to host not one, not two, but up to three so-called "super Earths".
Two planets have been definitively identified, one orbiting Gliese 887 every nine days and the other every 21 days.
Both planets are interior to, but close to the inner edge of, the liquid-water habitable zone.
"These planets will provide the best prospects for more detailed studies, including the search for life outside our solar system", said Jeffers.
The researchers also detected an unconfirmed signal, raising hopes of a third planet with a more "temperate" orbit, but they are "cautious" about the finding. "If someone had to live around a red dwarf, they would want to choose a quieter star like GJ 887", writes Melvyn Davies in a related Perspective.
The astronomers also found that the red dwarf is less active than our Sun. Scientists note that these new planets can have a thicker atmosphere than Earth, and may even host life. "By a quiet star, I mean that it doesn't have the dark starspots or the energetic outbursts [flares] that we see on the Sun".
An artist's impression of the multiplanetary system of super-Earths orbiting the nearby red dwarf star Lacaille 9352.
Another thing that the researchers found is that Gliese 887's brightness is quite constant, which would make future studies of the super-Earths' atmospheres much easier. The research team led by the University of Göttingen was able to detect a pair of large rocky bodies orbiting this small star, and they say there might be a third.
This planetary system will be a key target for study using NASA's next-generation James Webb Space Telescope, due for a 2021 launch, Jeffers said. Still, "we've been looking for exoplanets orbiting Gliese 887 for almost 20 years, and while we saw hints of a planetary signal, it wasn't strong enough to convince ourselves that it was a planet", study lead author Sandra Jeffers, an astrophysicist at the University of Göttingen in Germany, told Space.com.