Diamond exoplanet 55 Cancri e

55 Cancri e is a rocky exoplanet a strongly irradiated super earth, which has a diameter twice as large as that of the earth, or ≈ 25 000 km.
It is located about 40 light years (12 parsecs) of the solar system in the constellation Cancer.
55 Cancri e was discovered in 2004 by examining the radial velocity variations of the star.
The binary system 55 Cancri is composed of a yellow dwarf star, 55 Cancri A, similar to our Sun, and a red dwarf star, 55 Cancri B separated from A by more than 1000 AU (1 AU = 149 597 870 700 meters).
55 Cancri e discovery is the fifth planet around 55 Cancri A, since 2007. Three of these planets are gas giants like Jupiter, while the planet 55 Cancri e, closest to 55 Cancri A is rocky.
Since many scientists observe planets orbiting their sun, it seems that the exoplanets one to four times the size of Earth is abundant in the galaxy. Planet 55 Cancri e is not in the habitable zone of its star as the Earth relative to the sun. On the contrary it is very close to its star, it turns around it in 17 hours 46 minutes only. But the most surprising is that the French-American team of astronomers who discovered this very hot planet thinks it is largely composed of diamond.
"The surface of this planet is probably covered with graphite and diamond rather than water and granite", "This is our first glimpse of an exoplanet rock with a chemical composition radically different from that of the Earth," said Nikku Madhusudhan Yale University in the journal Astrophysical Journal Letters.
Density 55 Cancri e is close to the lead, its weight is 8.57 times that of the earth, so that its size is only two times that of the Earth.
It is very inhospitable, its surface temperature reaches 2148 degrees Celsius due to its proximity (2,393,000 km) with its star.
In 2011 astronomers had measured the radius for the first time bur in 2012, thanks to computer models, they were able to estimate its mass and also refine the chemical composition of the planet.

This is a simulation information from all possible combinations of elements that researchers have deduced the main features. The conclusion is surprising, it is composed mainly of carbon as graphite, diamond, iron and silicon. According to scientists, the diamond could fill a huge part of the world, at least one third of the mass of 55 Cancri e. Inside our Earth is oxygen rich but very poor in carbon, said Kanani Lee, a geophysicist at the University of Yale, one of the other co-authors of the study. The identification of this super-Earth carbon rich means that "we can no longer assume that remote rocky planets have the same chemical composition, the same internal structure and atmosphere than Earth," Nikku Madhusudhan. According to the scientists, this discovery opens new avenues for studying geochemical processes and geophysical exoplanets whose size is close to that of the Earth. Olivier Mousis, a planetary scientist at the Institute of Astrophysics Research in Toulouse, France, is also co-author of the study. 

NB: 55 Cancri system has a vast area of ​​stability between planets c and d could harbor additional planets similar to Earth. On 6 July 2003 a radio message called Cosmic Call 2 was sent toward 55 Cancri via radar antenna 70 meters in Eupatoria Ukraine, on the Black Sea coast. This message will arrive in 2044.