55 Cancri D
55 Cancri D is a Exoplanète orbits about it around 55 Cancri. (Other designations: Rho1 Cancri D , HD 75732 D ).
Planetary system
In 1996, one discovered a planet orbits about it around 55 Cancri has, similar to that detected little before in the system 51 Pegasi. At the same time, one announced the discovery of two another planets around two other planetary systems (around the stars τ Bootis and υ Andromedae). The planet was detected by measuring the radial Speed, whose periodicity of 14,7 Jour S corresponded to a planet having a mass equivalent to 78% of that of Jupiter. This planet was named 55 Cancri B , but to distinguish it from the star 55 Cancri B, it is called also 55 Cancri Ab . The radial velocity measurements taken for this planet showed an unexplainable shift. Only the gravitational influence of a more distant object could explain this variation.In 1998, one announced the probable discovery of a possible disc of dust around 55 Cancri A. One at least estimated the ray disc of dust at 40 UA, it is equivalent to the Ceinture of Kuiper of our solar system. Its slope is of 25° on the plan of the sky. Despite everything, this discovery could not be checked, and it was considered even erroneous. Indeed, one allotted this observation to cosmic radiations.
In 2002, after many radial velocity measurements, the researchers were able to announce the discovery of a new planet, 55 Cancri D , at an approximate distance of 5 astronomical units. At that time, it was thought that the eccentricity of the orbit was very weak (lower than 0,1), but this value was re-examined with the rise following additional observations. Even by taking into account these the first two planets, a 43 days periodicity remained, can be because of a third planet. The assumption was put forth that this signal was caused by the stellar activity. The third supposed planet was named 55 Cancri C.
In 2004 the discovery of a planet of the mass of Neptune, indicated under the name of 55 Cancri E was officialized. It buckles an orbit around its sun in 2,8 days. This planet can be a gas Géante of small size, or a very large telluric Planet. The observations carried out to discover 55 Cancri E confirm the existence of 55 Cancri C. Moreover, the astrometrical data carried out by the Space telescope Hubble enabled us to estimate the slope orbit of this external planet: 53° on the plan of the sky. On the basis of the postulate which the system is Coplanaire, that means that the real masses of planets are 25% more important than envisaged (the low assumptions formulated hitherto used the method radial speed).
In 2005, the existence of a hypothetical planet E was called into question by Jack Wisdom, after a meticulous re-examination of the data. According to him, instead of a planet which would buckle its orbit in 2.8 days, there would be a planet of a mass similar to Neptune, on a 261 days orbit (either 0.77 UA in term of distance). The assumption of this researcher was not confirmed.
Even if one does not take account of this planet E, data-processing simulations suggest that the system of 55 Cancri shelters a vast zone of stability (between the planets C and d) which could shelter additional planets. Moreover, the data-processing models predict that planets comparable with the Earth are suitable for be formed in the interstice between Cancri C and D, even if these planets (present in possible a " zone habitable") are undetectable with our current technologies. This planetary system is thus of an interest for the exobiologists.