Kepler- 78b : an exo- planet, Earth twin .

Astronomers have discovered a terrestrial (** ) exoplanet (*) the size of ower Earth.

This planet , named Kepler - 78b was discovered by the Kepler space telescope of NASA launched in 2009 to discover Earth -like planets orbiting to distant stars . For 4 years , the "family Kepler " is expanding and many rocky planets have been identified , of different sizes .

Two different research teams have confirmed and characterized Kepler-78b by ground-based telescopes : to determine its mass , they are using the radial velocity method to measure the influence of the gravitational drag of a planet on the oscillations of its star. On the other hand , Kepler sat. determines the size or the planetary radius by the amount of starlight obscured by the passage of the planet in front of his "sun" .

Comparison between our Earth and the planet Kepler- 78b - NASA doc / Credit: David A. Aguilar ( CfA )

Kepler- 78b is 1.2 times the size of Earth, and is 1.7 times more massive , which makes its density similar to the Earth's density , and suggests a rock / iron comparable composition .

His star is a bit smaller and less massive than our sun, and located at 400 light-years from Earth in the constellation Cygnus . Kepler- 78b goes around its star in just eight hours and a half, is much closer and seems to have a permanent one side to it . The temperature of this face is 2000-2800 ° C , making life impossible on the planet ... molten !
                   Artist's view of Kepler- 78b and its star - Karen Teramure (UH - IfA)

Kepler- 78b may not have always had this configuration. It could have been more massive and have an atmosphere at the time of its formation. Its migration to its star have caused the loss of the atmosphere. What remains today of the original planet is the heart of a once larger planet.

Kepler- 78b is a paradise for astronomers , but a hell for all life.

Glossary :
(*) Exo- planet : a planet in broad theme , located outside our solar system
(**) terrestrial : a terrestrial planet , as opposed to gaseous planets , a planet composed of rock and metal .

Sources :

- Nasa news – Scientists Discover the First Earth-Sized Rocky Planet – by Michele Johnson 650-604-6982 Ames Research Center, Moffett Field, Calif. - link   

- Nature – An Earth-sized planet with an Earth-like density – by Francisco Pepe & al. - link    

- Nature- A rocky composition for an Earth-sized exoplanet – by A.W.Howard & al. - link 

- Kepler’s Tally of Planets -  link