55 Cancri d

Planetbox begin
name=55 Cancri dPlanetbox 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=5.77 ± 0.11cite journal | url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2008ApJ...675..790F&db_key=AST&nosetcookie=1| 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=0.025 ± 0.03
period=5218 ± 230
ang_dist=430
long_peri=181.3 ± 32
t_peri=2,452,500.6 ± 230
semi-amp=46.85 ± 1.8Planetbox character
mass=>3.835 ± 0.08Planetbox discovery
discoverers=Marcy et al.
discovery_site=California, USA
discovery_method=Radial velocity
discovery_date=June 13, 2002
discovery_status=PublishedPlanetbox catalog
names=Rho¹ Cancri d, HD 75732 d

55 Cancri d is an extrasolar planet in a long-period orbit around the Sun-like star 55 Cancri A. Located at a similar distance from its star as Jupiter is from our Sun, it is the fifth and outermost known planet in its planetary system. 55 Cancri d was discovered on June 13, 2002.

Discovery

Like the majority of known extrasolar planets, 55 Cancri d 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.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2002ApJ...581.1375M&db_key=AST&nosetcookie=1|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] The same measurements also indicated the presence of another inner planet, designated 55 Cancri c.

Orbit and mass

When 55 Cancri d was discovered, it was thought to be on a fairly low eccentricity orbit similar to Jupiter in our solar system, though the orbital elements were not well determined. As more data was collected, the best-fit solution for this planet turned out to be highly eccentric, more so than any of the planets in our solar system (including Pluto).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] In 2008, after a complete orbit of this planet had been observed, the true orbit was revealed, indicating that as had been originally suspected, the planet's orbit was in fact near-circular, located about 5.77 AU from the star.

A limitation of the radial velocity method used to discover 55 Cancri d is that only a lower limit on the planet's mass can be obtained. In the case of 55 Cancri d, this lower limit was around 3.835 times the mass of Jupiter. In 2004, astrometric measurements with the Fine Guidance Sensors on the Hubble Space Telescope suggest that the planet's orbit is inclined by around 53° with respect to the plane of the sky. If this measurement is confirmed, it implies that the planet's true mass is 25% greater than the lower limit, at around 4.8 Jupiter masses.

Characteristics

Given the planet's high mass, the planet is a gas giant with no solid surface. Since the planet has only been detected indirectly, parameters such as its radius, composition and temperature are unknown.

Assuming a composition similar to that of Jupiter and that the planet's atmosphere is close to chemical equilibrium, it is predicted that 55 Cancri d is covered in a layer of water clouds: the planet's internal heat probably keeps it too warm to form the ammonia-based clouds that are typical of Jupiter. Its surface gravity is likely to be about 4 times stronger than Jupiter, or about 10 times that of Earth which is because the radius of the planet is unlikely to be much more than Jupiter's. [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]

References

ee also

* 55 Cancri b
* 55 Cancri c
* 55 Cancri e
* 55 Cancri f

External links

* [http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=%2A+55+Cnc+d SIMBAD: * 55 Cnc d -- Extra-solar Planet Candidate]
* [http://exoplanet.eu/planet.php?p1=55+Cnc&p2=d The Extrasolar Planets Encyclopaedia: Notes for Planet 55 Cnc d]
* [http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=192 Extrasolar Visions: 55 Cancri d]