55 Cancri c

Planetbox begin
name=55 Cancri cPlanetbox star
star=55 Cancri A
constell=Cancer
RA=RA|08|52|35.8
DEC=DEC|+28|19|51
dist_ly=40.9
dist_pc=12.5
class=G8VPlanetbox orbit
semimajor=0.240 ± 0.00005cite journal | author = Fischer, D.A. "et al." |url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2008ApJ...675..790F&db_key=AST&nosetcookie=1| title=Five Planets Orbiting 55 Cancri |journal=Astrophysical Journal |issue=675| page=790-801 |doi=10.1086/525512 |month=March |year=2008]
eccentricity=0.086 ± 0.052
period=44.3446 ± 0.007
ang_dist = 18
long_peri=77.9 ± 29
t_peri=2,449,989.3385 ± 3.3
semi-amp=10.18 ± 0.43Planetbox character
mass=>0.169 ± 0.008Planetbox discovery
discoverers=Marcy et al.
discovery_site=California, USA
discovery_date=June 13, 2002
discovery_method=Radial velocity
discovery_status=PublishedPlanetbox catalog
names=Rho¹ Cancri c, HD 75732 c

55 Cancri c is an extrasolar planet in an eccentric orbit around the Sun-like star 55 Cancri A, making one revolution every 44.34 days. It is the third known planet in order of distance from its star. 55 Cancri c was discovered on June 13, 2002 and has a mass comparable to that of Saturn.

Discovery

Like the majority of known extrasolar planets, 55 Cancri c was detected by observing changes in its star's radial velocity. This was achieved by making sensitive measurements of the Doppler shift of the star's spectrum. At the time of discovery, 55 Cancri A was already known to possess one planet (55 Cancri b), however there was still a drift in the radial velocity measurements which was unaccounted-for. [cite journal|url=http://www.journals.uchicago.edu/doi/full/10.1086/310444|author=Butler, R. et al.|title=Three New 51 Pegasi-Type Planets|journal=The Astrophysical Journal|volume=474|year=1997|pages=L115 – L118|doi=10.1086/310444]

In 2002, further measurements revealed the presence of a long-period planet in an orbit at around 5 AU from the star. Even when both of the two planets were accounted for, there was still a periodicity at around 43 days. However this period is close to the rotation period of 55 Cancri A, which led to the possibility that the 43-day period was caused by stellar rotation rather than a planet. Both the 43-day planet (designated 55 Cancri c) and the 5 AU planet (designated 55 Cancri d) were announced in the same paper, labelled in order of increasing distance from the star. [cite journal|url=http://www.citebase.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0207294|author=Marcy, G. et al.|title=A planet at 5 AU Around 55 Cancri|journal=The Astrophysical Journal|volume=581|pages=1375 – 1388|year=2002|doi=10.1086/344298]

Further measurements which led to the discovery of the inner planet 55 Cancri e in 2004 lent support to the planet hypotheseis.cite journal|url=http://xxx.lanl.gov/abs/astro-ph/0408585|author=McArthur, B. et al.|title=Detection of a NEPTUNE-mass planet in the ρ¹ Cnc system using the Hobby-Eberly Telescope|journal=The Astrophysical Journal|volume=614|year=2004|pages=L81 – L84|doi=10.1086/425561] Photometric measurements of the star over 11 years show no activity with the same period as 55 Cancri c's radial velocity variations, and furthermore the period is stable over long timescales, which is inconsistent with the hypothesis of stellar activity causing the radial velocity variations. The amplitude of the radial velocity signal is inconsistent with stellar variations on stars with 55 Cancri A's low level of chromospheric activity.

Orbit and mass

In the 5-planet solution for the 55 Cancri system, the orbit of 55 Cancri c is mildly eccentric: at apoastron the planet is about 19% further from the star as it is at periastron. It is located closer to 55 Cancri A than Mercury is to our sun, though it has a longer orbital period than the hot Jupiters. The planet is located close to a 3:1 resonance with the inner planet 55 Cancri b, however simulations indicate that the two planets are not actually in this resonance.

A limitation of the radial velocity method used to discover the planet is that only a lower limit on the mass can be obtained. Further astrometric observations with the Hubble Space Telescope on the outer planet 55 Cancri d, on the other hand, suggest that planet is inclined at 53° to the plane of the sky. The system is further expected to be coplanar. If all this is confirmed, this would mean the true mass of 55 Cancri c is about 0.21 times that of Jupiter.

Characteristics

Since the planet was detected indirectly through observations of its star, properties such as its radius, composition and temperature are unknown. With a mass similar to that of Saturn, 55 Cancri c is likely to be a gas giant with no solid surface.

References

ee also

* 55 Cancri b
* 55 Cancri d
* 55 Cancri e
* 55 Cancri f

External links

* [http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=%2A+55+Cnc+c SIMBAD: * 55 Cnc c -- Extra-solar Planet Candidate]
* [http://exoplanet.eu/planet.php?p1=55+Cnc&p2=c The Extrasolar Planets Encyclopaedia: Notes for Planet 55 Cnc c]
* [http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=10 Extrasolar Visions: 55 Cancri c]