55 Cancri (Rho1 Cancri)
A visual binary star system in the constellation Cancer consisting of a middle-aged, Sun-like
primary of high metallicity, 55 Cancri
A, and a red dwarf companion, 55 Cancri
B. (55 Cancri is the star's Flamsteed
designation. Its Bayer designation is Rho1 Cancri.) The component stars are separated by a mean
distance of about 1,150 astronomical units (172 billion km, or 108 billion
miles). In orbit around the primary have been discovered five planets which,
in order of increasing distance are Ae, Ab, Ac, Af, and Ad. This is the
largest number of planets currently known to exist around a star other than
|Comparison of the solar system with
the 55 Cancri system
Ae, the innermost planet, is about 8 times as massive and twice as big as
the Earth, making it the first super-Earth to be found around a main sequence
star. It moves in a tiny orbit that must result in an extremely high surface
temperature. At first it was thought that Ae might be a water planet, covered
in a deep ocean of supercritical water, but hydrogen was never found in
its spectrum. An alternative suggestion, put forward in 2012 is that at
least a third of the planet consists of carbon, most of which may be in
the form of diamond.
Ab, the second planet, is an epistellar
Jovian, or "hot Jupiter," only the fourth extrasolar planet
of all to be discovered. It circles the host star at less than one third
the distance of Mercury from the Sun and
has a warm, puffy atmosphere which is slowly evaporating into space. The
third planet, Ac, is a Saturn-sized world
in a highly elliptical orbit that takes it well within intra-Mercurian distance
of the star. The fifth planet, Ad, is a high-mass classical
Also surrounding 55 Cancri A is a dust disk, which is presumably a regenerated
disk, extending out to about 40 astronomical units from the star with
an inclination of about 25°.3, 4, 5
55 Cnc was one of the five targets of the Feb. 14, 2003 "Cosmic Call" initiative
(see interstellar radio messages).
| Host star (55 Cancri A)
||40.9 light-years (12.5 pc)
||4,980°C (5,250 K)
|luminosity (Sun = 1)
|mass (Sun = 1)
|mass (Jupiter = 1)
|year of discovery
||Marcy et al7
||Marcy et al2
||Marcy et al6
||Marcy et al
||Marcy et al6
|method of discovery
- Gonzalez, G., and Vanture, A. "Parent Stars of Extrasolar Plnets III:
Rho1 Cancri Revisited," Astronomy & Astrophysics, 339, L29 (1998).
- Butler, P., Marcy, G., Williams, E., Hauser, H., and Shirts, P. "Three
New 51 Peg-type Planets," Astrophysical Journal Letters, 474,
- Baliunas, S., Henry, G. W., Donahue, R. A., Fekel, F. C., and Soon,
W. H. "Properties of Sunlike Stars with Planets," Astrophysical Journal
Letters, 474, L119 (1997).
- Dominik, C., Laureijs, R. J., Jourdain de Mouizon, M., and Habing,
H. J. "A Vega-like Disk Associated with the Planetary System of Rho1 Cancri," Astronomy & Astrophysics, 329, L53 (1998).
- Trilling, D., and Brown, R. "A Circumstellar Dust Disk Around a Star
with a Known Planetary Companion," Nature, 395, 775 (1998).
- Marcy G., Butler, P., Fischer D., Laughlin G., Vogt S., Henry G.,
and Pourbaix D. "A Planet at 5 AU Around 55 Cancri," ApJ., 581,
- McArthur B., Endl M., Cochran W., Benedict F., Fischer D., Marcy G.,
Butler P., Naef D., Mayor M;, Queloz D., Udry S., and Harrison T. "Detection
of a Neptune-Mass Planet in the 55 Cancri System by the HET," ApJ.
Letters, accepted (2004).
PLANETS AND SUBSTELLAR OBJECTS