Gliese 667 Cc

An extrasolar planet, Gliese 667 Cc orbits Gliese 667 C, which is part of a triple-star system. It lies at a distance of 22.1 light years from Earth within the Scorpius constellation.

Diameter: between 6.3 x 103 and 2.5 x 105 km
Mass: 2.01 x 1025
Composition: unknown
Orbit: 28 Earth days

Gliese 667Cc was discovered in April 2012 by an international group of astronomers working at the European Southern Observatory in the Atacama Desert, northern Chile. It is a super-Earth, some 3.4 times the mass of Earth, orbiting a red dwarf star, Gliese 667 C. At the time of its discovery, scientists called it the most Earth-like object outside of the Solar System.

The discovery was made with the High Accuracy Radial Planetary Searcher (HARPS) telescope. Gliese 667 Cc receives 10% less light from its star than the Earth receives from the Sun, but as this light is mostly in the infra-red part of the electromagnetic spectrum, its effect is that the energy received at its surface is the same as Earth receives from the Sun.

The planet orbits its star over a four-week period at a distance of 0.12 AU (17.9 million kilometres). The likelihood is that it is tidally locked to the star, meaning that it always shows the same hemisphere to the surface of Gliese 667 C.

The temperature on Gliese 667 C is 3,400K (Kelvin) compared with the Sun’s 5,778K. Its habitable zone lies in an orbit between 0.11 astronomical units (AU) (16.4 million kilometres) and 0.23 AU (34.3 million kilometres) from the star. Gliese 667 Cc’s orbital distance seems to be comfortably within the habitable zone, should liquid water be present on its surface.

The surface temperature of Gliese 667 Cc could be approximately 30C in the presence of liquid water, but if the atmosphere consists of more massive molecules, the temperature will be higher, making surface conditions inhospitable to life. The tidal locking adds further complications as one hemisphere of the planet experiences constant daylight while the other is permanently dark. The temperature differences between the two hemispheres will have a strong influence on the planet’s global climate. In addition, the planet will receive frequent flares from its host star.

A further complication is that the Gliese 667 C star is part of a triple-star system. Gliese 667 A and Gliese 667 B are about 230 AU (34.2 billion kilometres) away. Despite the distance, they would be visible from the surface of the planet. The Sun could also be seen as a distant star from the surface of Gliese 667 Cc.

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