Difference between revisions of "Rho(1) Cancri"

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The 55 or Rho(1) Cancri binary system is located about 40.3 light-years from Sol. It lies in the northeastern part of the constellation Cancer, the Crab. The system is a member of the Hyades group. The two stars are located about 1,100 AUs apart and seem to be gravitationally bound.

Rho(1) Cancri A

Rho(1) Cancri A is a yellow-orange main sequence dwarf star of spectral and luminosity type G8/K0 V, with around 0.94 +/- 0.05 times the mass of Sol^[1], 1.1 times its diameter^[2], and around 60 (57 to 62) percent of its bolometric luminosity^[1]. The star is now estimated to around twice as enriched as Sol with elements heavier than hydrogen ("metallicity") based on its abundance of iron, where metal enrichment may have been primordial^[1][3][2][4]. Chromospherically "inactive" with a rotation period of 39 days^[1], it appears to be a middle-aged dwarf at between two to eight billion years old^[3][2]

In October 1998, astronomers at the University of Arizona announced the apparent confirmation of a circumstellar dust disk that may be similar in composition to the Edgeworth-Kuiper (E-K) Belt of the Solar System. Detected dust appeared to extend from 27 to beyond 44 AUs out from Star A (possibly with a radius of around 50 AUs, which would be beyond the orbital distances of Neptune and Pluto from Sol). A subsequent study suggested that the sub-millimeter emissions were lower by a factor of 100 than previous thought, with a hole within around 10 AU of the star^[5]. Some astronomers now believe that the dust indications could be spurious, caused by background sub-millimeter emissions located near but not centered on 55 Cancri A^[3][6].

As of November 6, 2007, astronomers have announced the discovery of five planetary candidates around Star A.

Known Places around Rho(1) Cancri A

• Rho(1) Cancri Ab This planet is about 82.4 (but probably 103) percent of Jupiter's mass. It moves around Star A at an average distance of only 0.115 AUs in a slightly elliptical orbit that takes less than 14.7 days to complete.
• Rho(1) Cancri Ac A giant planet in a middle orbit, at about 0.24 AUs from Star A. Planet c has at least a sixth (16.9 percent) but probably has a fifth (21 percent) of Jupiter's mass and an eccentric orbit that takes less than 44.3 days to complete^[1].
• Rho(1) Cancri Ad Residual drift data provides solid evidence of an even larger planet in an outer orbit, now estimated to be about 5.77 AUs from Star A (between the average orbital distances of Jupiter and the Main Asteroid Belt in the Solar System). Planet d has at least 3.83 times the mass of Jupiter and a mildly eccentric orbit that takes around 14.7 years to complete^[1].
• Rho(1) Cancri Ae A Neptune sized planet, about 13.5 times Earth's mass. It orbits it's primary at approximately 0.038 AUs with a period of three days.
• Rho(1) Cancri Af Orbits at a distance of 0.781 AUs from this star, within its "habitable zone"^[7][1]. The planet has at least 45 Earth-masses but probably 57 Earth-masses and may be substantially composed of hydrogen and helium, like Saturn in the Solar System. It has an orbital period of around 260 days.

Rho(1) Cancri B

Rho(1) Cancri B is a red main sequence dwarf star of spectral and luminosity type M3.5-4 V, with about 13 percent of Sol's mass, 30 percent of its diameter, and 76/10,000th of its luminosity.

The orbit of an Earth-like planet (with liquid water) around Star B may be centered as close as 0.028 AU -- well within the orbit distance of Mercury -- with an orbital period of just over 4.6 days. Unfortunately, tidal locking of a planet in such a close orbit would result in perpetual day on one side (and perpetual night on the other).

(Data from SolStation.com)

Notes

1. ↑ ^{1.0 1.1 1.2 1.3 1.4 1.5 1.6} (Fischer et al, 2007)
2. ↑ ^{2.0 2.1 2.2} (Baliunas et al, 1997)
3. ↑ ^{3.0 3.1 3.2} (Marcy et al, 2002)
4. ↑ (Santos et al, 2001)
5. ↑ (Jayawardhana et al, 2000)
6. ↑ (Schneider et al, 2001)
7. ↑ (NASA JPL press release)