Three planets in the life zone of a nearby star

A study by the Southern European Telescope Consortium reexamines the Gliese 667c Reexamined family which, as its name suggests, is the third in a triple star system. Citrus on these planets enjoy three suns in the sky

A team of astronomers combined new observations of the star Gliese 667C with previous data from the 3.6-meter HARPS telescope of the European Southern Observatory in Chile, revealing that the star hosts a solar system with at least six planets.

No fewer than three of these planets are super-Earths that reside in the region around the star where liquid water can exist. This makes them possible candidates for the presence of life. This is the first system discovered with a high density of planets in the habitable zone.

Gliese 667C is a well-studied star. Its mass is slightly more than a third of the mass of the Sun. It is part of a triple star system known as Gliese 667 (also known as GJ 667). It is only 22 light years away from us in the Scorpio group. This is a spitting distance from the cosmic point of view. Planets much further away than him were discovered using the Kepler space telescope.

In previous studies, only three of the seven holiday planets were discovered around Gliese 667C, one of which is in the habitable zone. Now researchers from the University of Gottingen in Germany, the University of Washington in the US and the University of Herefordshire in the UK have published a study in which they re-examined the previous HARPS observations of the system plus new observations with the European Southern Observatory's Very Large Telescope, the Keck Telescope in Hawaii and the Magellan Space Telescope. From the new data it appears that four more planets have been added to the existing picture.

The planets orbit the faint star in a three-star system. The observer on the ground of one of the planets orbiting these suns will be able to see the other two suns - apart from his own - as a pair of bright stars in the sky that are also visible during the day and will provide illumination like that of the full moon at night.
The new planets fill the habitable zone of Gliese 667C because there are no longer stable orbits where the planets can exist at a reasonable distance from each other. "We know that the star already had three planets from previous studies, so we wanted to see if there were a few more," says Miko Tomi from the University of Hertfordshire. "By adding observations and reexamining existing data we were able to find even more. The detection of three low-mass planets in the habitable zone is very exciting."

Three of the planets have been confirmed as "super-Earths" - that is, stars more massive than Earth but smaller than planets such as Uranus and Neptune (Uron and Rahab). All three are in the habitable zone, a thin shell around the star where water can exist in a liquid state if the other conditions are right. This is the first time that three planets have been observed orbiting in the habitable zone of the same system.

"The number of potential life-supporting planets in our galaxy may increase if, instead of the average of one rocky planet in 10 solar systems, we also find a system where three such planets are in the habitable zone." said Rory Barnes from the University of Washington in the US, one of the signatories of the article.

Compact solar systems surrounding sun-like stars are very common in the Milky Way. Around such stars, the planets orbit too close to the star and then they will be too hot to be able to support life, but this is not true for cold and dim stars such as Gliese 667C. In this case, the area of ​​life resides entirely outside an orbit similar to that of our planet Mercury, that is, much closer to the sun. A lot. The Gliese 667C system is the first example of a system where low-mass stars appear to host several rocky planets in the habitable zone.

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