to discover 55 Cancri d is that only a lower limit on the planet's mass can be obtained. In the case of 55 Cancri d, this lower limit was around 3.835 times the mass of Jupiter. In 2004, astrometric measurements with the Fine Guidance Sensors on the Hubble Space Telescope suggest that the planet's orbit is inclined by around 53° with respect to the plane of the sky. If this measurement is confirmed, it implies that the planet's true mass is 25% greater than the lower limit, at around 4.8 Jupiter masses; and that 55 Cancri d is not coplanar with the innermost planets e and b (both at about 85°). This measurement is dependent on the planet's accurate orbital period, estimates for which have changed since 2004. Characteristics Given the planet's high mass, the planet is a gas giant with no solid surface. Since the planet has only been detected indirectly, parameters such as its radius, composition, and temperature are unknown. Assuming a composition similar to that of Jupiter and that the planet's atmosphere is close to chemical equilibrium, it is predicted that 55 Cancri d is covered in a layer of water clouds: the planet's internal heat probably keeps it too warm to form the ammonia-based clouds that are typical of Jupiter. Its surface gravity is likely to be about 4 to 5 times stronger than Jupiter, or about 10 to 15 times that of Earth which is because the radius of the planet is unlikely to be much more than Jupiter's and is probably slightly smaller than Jupiter due to the high metal content in the parent star. See also Appearance of extrasolar planets Cancer (Chinese astronomy) Lists of exoplanets Gliese 1132 b, Rocky exoplanet with a confirmed atmosphere. Mu Arae c, At constellation Ara Planetary system References External links 55 Cancri Cancer (constellation) Exoplanets discovered in 2002 Giant planets Exoplanets detected by radial velocity Exoplanets detected by astrometry Exoplanets with proper names