Gliese 581

Gliese 581 g, an exoplanet in the Libra

Gliese 581 is a red dwarf located in the constellation Libra to 20.5 light years from us. This star has a mass equal to 1/3 of the mass of our Sun. In 2009, Gliese 581 is the 87th closest known star. Six exoplanets have been detected around the red star, two, Gliese 581 c and Gliese 581 d is the first exoplanet to have been found in the habitable zone of this star. At 20 light years from us, the red dwarf in recent years is the subject of attention. Indeed, astronomers point their telescopes permanently in his direction. Of telescopes on Earth have detected in the oscillations of the star, the trace of a multiple planetary system, whose the existence of some planets is contested (Gliese 581 d and g). Two planets are situated near the habitable zone of their star. The circumstellar habitable zone or ecosphere is a theoretical sphere surrounding a star where the temperature on the surface of planets orbiting it would allow the appearance of liquid water. A team led by Steven Vogt (UCO Lick) and Paul Butler (Carnegie DTM Inst.). Announced in October 2010, the detection of a planet around Gliese over 581. Set this time it is located in the middle of the habitable zone of the star. This planet is a very serious contender under the first habitable planet orbiting a star very close. This planet is currently called Gliese 581 g, unfortunately, his existence is not certain. The data indicate that Gliese 581 g has a circular orbit of 37 days. Its semi-major axis is 0.146 astronomical unit (AU) and its mass is equivalent to 3.17 times that of Earth.

The models also predict that Gliese 581 g has a radius of 1.5 Earth and its surface gravity between 1.1 and 1.7 times that we have on Earth. The Gliese 581 system has an age estimated at 4.3 billion years almost equivalent to the age of our solar system. The discovery of a habitable terrestrial planet so close to ours suggests that they are numerous in our Galaxy. The discovery of exoplanets began in 1990 and 2010, 490 exoplanets were referenced.

Image: Illustration of the red dwarf Gliese 581 and Gliese 581 g ice planet. The name of the star Gliese 581 refers to the designation Gliese Catalogue, which lists the nearby stars.

NB: The astronomers classify stars in dwarf or giant. Gliese catalog, named Wilhelm Gliese (1915-1993), list the stars within 25 parsecs (25 x 3.08567758 × 10¹³ km).

The number of habitable planets increases!

A team of planet hunters led by astronomers from the University of California Santa Cruz and Carneegie Institute of Washington, delivered the results of their work in 2010.
They are derived from 11 years of observation.
"Our results offer a compelling case for a potentially habitable planet"
"The fact that we are able to detect this planet so quickly and so close to us that such a planet must be really normal." Said Steven Vogt.
Gliese 581 g is in synchronous rotation with its star.
One side is always facing the sun and the other in eternal night.
One effect of this feature is to stabilize the climate at the surface of the planet, according to S. Vogt.
The area would be the most livable line, called "Terminator," which defines the dark side, face lit up. Thus the surface temperature increase and decrease gradually according to the side.

"Depending on the longitude, emerging life forms have a wide range of climates stable to enable them to evolve" S. Vogt. This discovery changes the previous estimates of stellar systems in our galaxy, which may have a habitable planet. Given the relatively small number of stars that were followed closely by the planet hunters, this discovery came surprisingly quickly.
"If habitable planets are so rare, we should not have found one so quickly and so close to us."
"The number of systems with potentially habitable planets is probably about 10 or 20 percent, when you multiply that by hundreds of billions of stars in the Milky Way, there could be tens of billions of similar systems in our galaxy. "Steven Vogt

Image: Gliese 581 g is in synchronous rotation with its star. One side is always facing the sun and the other in eternal night.