55 Cancri e may be a planet that has a similar origin to Neptune, formed a long way from its star and which drew much closer to it later on. The intense radiation of its star caused the rapid evaporation of its original atmosphere which was not very dense, leaving only a core of rock and ice. The external layer of the planet, rich in volatile components, is also slowly evaporating, which in a few billion years will leave only a core of rock several times the mass of the Earth, like CoRoT 7, another Super-Earth. This scenario is only hypothetical 55 Cancri e could have a different origin and nature. According to some models, it could even be a solid planet lacking an atmosphere

Observing the transit of the planet at first 

55 Cancri e is an exoplanet which was discovered in 2005; by ground telescopes thanks to the method for calculating radial velocity (see Physicists from liége in seventh heaven). It is not so far from our Earth as it orbits the 55 Cancri star, at a distance of “only” 40 light-years and visible to the naked eye in the Cancer constellation. This makes it one of the closest exoplanets to our solar system.

A preliminary estimation assumed that there was a revolution, an orbital period of more than two days (compared with the 365,25 days that our planet takes to make a complete orbit of the sun). However, in 2009, a new analysis of the radial velocity reduced this period to less than a day! “It is therefore practically attached to its star. And this reassessment of the orbit greatly increased the chances of the planet transiting its star, that is to say that it eclipses each time it passes between it and the Earth (such a configuration makes possible a whole series of complementary measurements of the planet, Editor’s note.). The probability of a favorable alignment of the orbit went from 7 to 25%. Indeed, the nearer a planet is to its sun the greater the chances that it will partially hide it during each orbit”.

Just when this correction of the orbital period became known, Michaël Gillon, in association with researchers at MIT in Boston, led a research program on exoplanets in transit with the help of NASA’s spatial telescope Spitzer “We therefore decided to point the telescope at the 55 Cancri star, and we detected the transit which was a big surprise. This transit was also observed by the Canadian spatial telescope MOST. Because the planet has an almost circular orbit and it passes between the Earth and its star every eighteen hours, it must therefore also be occulted by its star with the same frequency each time it passes behind it. Knowing its size and radiation, we deduced that it would be possible to detect its thermal emission. We therefore directly launched this new study project continuing on from the discovery of the transit,” explains the delighted researcher.