Using new observations of Gliese 667C with existing data from HARPS at ESO's 3.6-metre telescope in Chile,
an international team of astronomers has found a system with at least six planets.
This is the first system found with a fully packed habitable zone.
Three of these planets are super-Earths lying in the zone around the star where liquid water could exist,
making them possible candidates for the presence of life.
Artist's impression of the Gliese 667C system. Credits: ESO / M. Kornmesser
Gliese 667C is a very well-studied star. Just over one third of the mass of the Sun, it is part of a triple
star system known as Gliese 667, 22 light-years away in the constellation of Scorpius (The Scorpion).
"We knew that the star had three planets from previous studies, so we wanted to see whether there were any more,"
"By adding some new observations and revisiting existing data we were able to confirm these three and
confidently reveal several more. Finding three low-mass planets in the star's habitable zone is very exciting!"
said Dr Mikko Tuomi of the University of Hertfordshire, UK.
This is quite close to us-within the Sun's neighbourhood-and much closer than the star systems investigated
using telescopes such as the planet-hunting Kepler space telescope.
Previous studies of Gliese 667C had found that the star hosts three planets with one of them in the habitable zone.
These planets orbit the third fainter star of a triple star system. Viewed from one of these newly found
planets the two other suns would look like a pair of very bright stars visible in the daytime and at night
they would provide as much illumination as the full Moon.
The new planets completely fill up the habitable zone of Gliese 667C, as there are no more stable orbits in
which a planet could exist at the right distance to it.
The planetary system around Gliese 667C
"The number of potentially habitable planets in our galaxy is much greater if we can expect to find several of
them around each low-mass star-instead of looking at ten stars to look for a single potentially habitable planet,
we now know we can look at just one star and find several of them," adds co-author Rory Barnes (University of
Compact systems around Sun-like stars have been found to be abundant in the Milky Way. Around such stars,
planets orbiting close to the parent star are very hot and are unlikely to be habitable. But this is not
true for cooler and dimmer stars such as Gliese 667C.
In this case the habitable zone lies entirely within an orbit the size of Mercury's, much closer in than
for our Sun. The Gliese 667C system is the first example of a system where such a low-mass star is seen to
host several potentially rocky planets in the habitable zone.
"These new results highlight how valuable it can be to re-analyse data in this way and combine results from
different teams on different telescopes."