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D. E. Trilling, R. H. Brown (LPL)
Radial-velocity searches have indirectly detected that a planet with minimum mass 0.84 times that of Jupiter ({\rm MJ}) orbits the star 55~Cancri, a 3~billion year old G8 star, with a period of 14.65~days and an orbital separation of 0.11~AU (Butler et al. 1997). Furthermore, the detection of excess far infrared emission from 55~Cancri is suggestive of circumstellar dust in that system (Dominik et al. 1998). We have reported results of an infrared coronagraphic search for a mature planetary system around 55~Cancri (Trilling and Brown 1998). We have found a circumstellar disk of material whose inferred mass is approximately 10~times that estimated for our Solar System's Kuiper Belt. The observed disk around 55~Cancri extends to at least 40~AU, consistent with the expected extent of our Solar System's Kuiper Belt (Weissman 1995). Our observations show that 55~Cancri's dust disk is relatively dark at 2.3~microns, consistent with absorption due to methane ice. Assuming that 55~Cancri's disk is coplanar with the radial-velocity planet's orbit, we measure the inclination of the system and find the planet's mass to be {1.9+1.1-0.4} {\rm MJ}. All the available evidence (a definite radial velocity companion; the suggestion of a second radial velocity companion in the system (Butler et al. 1997); the far infrared excess reported by Dominik et al.; and our imaging and characterization of a disk out to at least 40~AU) is suggestive of a mature planetary system around 55~Cancri.