Four planets are now known (or are at least suspected) to orbit 55 Cancri (Cnc), making it appear something like our own Solar System. In addition, the star has a distant red dwarf companion. Farthest out, at 5.9 Astronomical Units (AU) from the star, is the most massive, 55 Cnc-d, which is at least 4.1 times the mass of Jupiter and takes 14.7 years to orbit. The other three are much closer and less massive. Next in order are 55 Cnc c, b, and e with minimum masses of 0.21, 0.84, 0.045 solar, orbital radii of 0.24, 0.11, 0.038 AU, and periods of 44, 14.7, and 2.81 days. The existence of 55 Cnc-c is questionable. 55 Cnc-e has the smallest measured minimum mass, only about that of Uranus or Neptune. It is also closest to its parent star, its orbit just 10 percent the size of that of Mercury.
55 Cancri
Newfound Planetary System Has "Hometown" LookThe star, 55 Cancri in the constellation Cancer, was already known to have one planet, announced by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter and whips around the star in 14.6 days at a distance only one-tenth that from Earth to the Sun. Using as a yardstick the 93-million mile Earth-Sun distance, called an astronomical unit or AU, the newfound planet orbits at 5.5 AU, comparable to Jupiter's distance from our Sun of 5.2 AU (or about 512 million miles). Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter's orbital period of 11.86 years. It is 3.5 to 5 times the mass of Jupiter... The star 55 Cancri is 41 light years from Earth and is about 5-billion years old. Further data are needed to determine whether yet another planet is orbiting it, because the two known planets do not explain all the observed Doppler wobbling. One possible explanation is a Saturn-mass planet orbiting about .24 AU from the star.
NASA
Jet Propulsion Laboratory
University of California, Berkeley
June 13, 2002
Astronomers Discover Two More Neptune-Sized Planets[T]he planet recently discovered around the sun-like 55 Cancri completes a full orbit in less than three days, compared to the 365-day year of planet Earth. This Neptune-sized planet circles its star much more closely than the Earth orbits the Sun. In fact, it circles 55 Cancri at a distance of 3.5 million miles — less than 4% the distance between the Earth and the Sun. The other planet just announced — which circles Gliese 436 at a distance of 2.6 million miles — also orbits at relatively short range, at least when compared to Earth’s 93 million mile distance from the Sun... As the only four-planet system known thus far, in McArthur’s view the 55 Cancri system is “the closest analog we have to our own solar system.” In fact, the earlier detection of planets around 55 Cancri was sufficient reason to put it toward the top of the list of stars to be observed by the SETI Institute’s Project Phoenix, which looked at the star several years ago. Using a custom-made supercomputer and the National Radio Astronomy Observatory at Green Bank, West Virginia, 55 Cancri was examined as part of as part of the world’s most sensitive search for extraterrestrial intelligence. No signs of intelligence were found.
by Doug Vakoch
SETI Institute
September 2, 2004
55 (Rho1) Cancri 2The star may be roughly twice (186 percent) as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Marcy et al, 2002, in pdf; and exoplanets.org). It appears to be either a super metal-rich dwarf or a slightly metal-poor K0 subgiant (Baliunas et al, 1997), but a recent study suggests that the metals enrichment may have been primordial (Santos et al, 2001). According to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 3522, enhanced CN and C2 and perhaps CH has been detected in its spectrum. The star may be between two to eight billion years old (e.g., five billion years old, see: Marcy et al, 2002, in pdf; and Baliunas et al, 1997) -- appearing to be middle aged and chromospherically inactive. 55 Cancri A has a widely separated, dim companion Star ("B") located about 1,100 AUs (85" at 40.9 ly) away that seems to be gravitationally bound to it.
Sol Station
Sun and planets:55 Cancri b is a massive planet, orbiting very close to its parent star. In this respect it is similar to 51 Pegasi b, though these two worlds are different in some important aspects. Both planets are sufficiently massive to retain an atmosphere, but for 51 Pegasi b, it will be blown into space by the nearby star. 55 Cancri b has more than twice the orbital radius than 51 Pegasi b and a higher mass, so it would retain most of its gases. If it actually formed at its current position, an issue highly disputed among scientists, it would have a large, rocky core. With its high mass and dense atmosphere, 55 Cancri b may look like a hybrid between Venus and Jupiter.
55 Cancri system:
Extrasolar Planets: 55 Cancri
There are strong sources of heat on 55 Cancri b. One of them is the intense radiation from the nearby star, but another source is tidal friction caused by the star's gravity. The planet's surface may even be completely molten. Enormous volcanic eruptions would fill the atmosphere with carbondioxide and sulphur compounds, producing a thick yellowish cloud cover. Any daring explorer would be crushed by the immense pressure at ground level, and vaporized by the heat - and he could not even see the disk of dust recently discovered around 55 Cancri.
No known form of life could exist on 55 Cancri b. A volcanically hyperactive world, where pure sulphuric acid rains on oceans of molten rock, and titanic strikes of lightning from earth-sized thunderclouds give an eerie illumination, 55 Cancri b would be among the best places to call Hell.
Orbital Parameters and Planet Mass
Data provided by California & Carnegie Planet Search Team
Lick Observatory
Latest Orbital Parameters Planet Period Tperi (JD-2450000) ecc omega (deg) Vel Amp, K (m/s) M sin i (Mjup) a (AU) b 14.653 d 1.479 .02 99 72.2 0.84 0.115 c 44.28 d 31.4 .34 61 13.0 0.21 0.24 d 5360 d 2785 .16 201 49.3 4.05 5.9 The inner planet was announced by Butler et al. in January 1997. Analysis of extended velocity measurements reveals additional velocity variations.
