55 Cancri b

Planetbox begin
name=55 Cancri bPlanetbox 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=0.115 ± 0.0000011cite journal | author =DA Fischer "et al." | title=Five Planets Orbiting 55 Cancri |journal=Astrophysical Journal |issue=675| page=790-801 |doi=10.1086/525512 |month=March |year=2008]
eccentricity=0.014 ± 0.008
period=14.65162 ± 0.0007
ang_dist = 8.582
long_peri=131.94 ± 30
t_peri=2,450,002.94749 ± 1.2
semi-amp=71.32 ± 0.41Planetbox character
mass=>0.824 ± 0.007Planetbox discovery
discovery_date=April 12, 1996
discovery_site=California, USA
discovery_method=Radial velocity
discoverers=Butler, Marcy
discovery_status=PublishedPlanetbox catalog
names=55 Cancri Ab, Rho¹ Cancri b, HD 75732 b

55 Cancri b (occasionally referred to as 55 Cancri Ab in order to distinguish it from the star 55 Cancri B) is an extrasolar planet orbiting the Sun-like star 55 Cancri A every 14.65 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter. Discovered in 1996 by Geoffrey Marcy and R. Paul Butler, 55 Cancri b was the fourth known extrasolar planet, excluding pulsar planets.

Discovery

Like the majority of known extrasolar planets, 55 Cancri b was discovered by detecting variations in its star's radial velocity caused by the planet's gravity. By making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A, a 15-day periodicity was detected. The planet was announced in 1996, together with the planet of Tau Boötis and the innermost planet of Upsilon Andromedae. [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]

Even when this inner planet, with a mass at least 78% times that of Jupiter was accounted for, the star still showed a drift in its radial velocity. This eventually led to the discovery of the outer planet 55 Cancri d in 2002.

Orbit and mass

55 Cancri b is in a short-period orbit, though not so extreme as that of the previously detected hot Jupiter 51 Pegasi b. The orbital period indicates that the planet is located close to a 1:3 mean motion resonance with 55 Cancri c, however investigations of the planetary parameters in a Newtonian simulation indicate that while the orbital periods are close to this ratio, the planets are not actually in the resonance.

A limitation of the radial velocity method used to discover the planet is that only a lower limit on the mass can be determined. Astrometric measurements made with the Hubble Space Telescope suggest that the outer planet is inclined at around 53° with respect to the plane of the sky. [cite journal|url=http://xxx.lanl.gov/abs/astro-ph/0408585|author=McArthur 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] The system is further expected to be coplanar. Assuming all this is confirmed, the planet's true mass is around 1.03 Jupiter masses.

Characteristics

Given the planet's high mass, it is likely that 55 Cancri b is a gas giant with no solid surface. Since the planet has only been detected indirectly, properties such as its radius, composition and temperature are unknown. Assuming a composition similar to that of Jupiter and that its environment is close to chemical equilibrium, 55 Cancri b is predicted to have a cloudless upper atmosphere with a spectrum dominated by alkali metal absorption. [cite journal|url=http://adsabs.harvard.edu/abs/2003ApJ...588.1121S|author=Sudarsky, D. et al.|title=Theoretical Spectra and Atmospheres of Extrasolar Giant Planets|journal=The Astrophysical Journal|volume=588|issue=2|pages=1121 – 1148|year=2003|doi=10.1086/374331]

The planet is unlikely to have large moons, since tidal forces would either eject them from orbit or destroy them on short timescales relative to the age of the system. [cite journal|url=http://adsabs.harvard.edu/abs/2002ApJ...575.1087B|author=Barnes, J., O'Brien, D.|title=Stability of Satellites around Close-in Extrasolar Giant Planets|journal=The Astrophysical Journal|volume=575|issue=2|pages=1087 – 1093|year=2002|doi=10.1086/341477]

References

ee also

*55 Cancri c
*55 Cancri d
*55 Cancri e
*55 Cancri f
*Appearance of extrasolar planets

External links

* [http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=%2A+55+Cnc+b SIMBAD: * 55 Cnc b -- Extra-solar Planet Candidate]
* [http://exoplanet.eu/planet.php?p1=55+Cnc&p2=b The Extrasolar Planets Encyclopaedia: Notes for Planet 55 Cnc b]
* [http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=9 Extrasolar Visions: 55 Cancri b]