47 Ursae Majoris c

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**47 Ursae Majoris c**
Parent star
Extrasolar planet		Lists of extrasolar planets
Star		47 Ursae Majoris
Constellation		Ursa Major
Right ascension	(α)	10^h 59^m 28.0^s
Declination	(δ)	+40° 25′ 49″
Spectral type		G1V
Orbital elements
Semimajor axis	(a)	3.79 ± 0.24 AU
Eccentricity	(e)	0.00 ± 0.12
Orbital period	(P)	2594 ± 90 d
Inclination	(i)	?°
Longitude of periastron	(ω)	127 ± 56°
Time of periastron	(τ)	2,451,360 ± 500 JD
Physical characteristics
Mass	(m)	>0.79 ± 0.13 M_J
Radius	(r)	? R_J
Density	(ρ)	? kg/m³
Temperature	(T)	? K
Discovery information
Discovery date		2002
Discoverer(s)		Fischer, Butler, Marcy, et al.
Detection method		Doppler Spectroscopy
Discovery status		Confirmed

47 Ursae Majoris c is an extrasolar planet orbiting the Sun-like star 47 Ursae Majoris, making one orbital revolution every 2,594 days. The planet was discovered in 2002 and has a mass at least 79% that of Jupiter. 47 Ursae Majoris c is the outermost known planet in its planetary system.

1 Discovery
2 Orbit and mass
3 Characteristics
4 See also
5 References
6 External links

[edit] Discovery

Like the majority of known extrasolar planets, 47 Ursae Majoris c was discovered by detecting changes in its star's radial velocity caused by the planet's gravity. This was done by measuring the Doppler shift of the star's spectrum.

At the time of discovery, 47 Ursae Majoris was already known to host one extrasolar planet, designated 47 Ursae Majoris b. Further measurements of the radial velocity revealed another periodicity in the data unaccounted for by the first planet. This periodicity could be fitted by assuming a second planet, designated 47 Ursae Majoris c existed in the system with an orbital period close to 7 years. Observations of the photosphere of 47 Ursae Majoris suggest that the periodicity could not be explained by stellar activity, making the planet interpretation more likely. The planet was announced in 2002.^[1]

A more recent study with additional data points cannot confirm the original orbital solution. Still, the study does not dismiss the existence of a second planet around 47 Ursae Majoris. The planet may orbit further out, best orbital solution gives a period of 7586 days (almost 21 years). However, more data is required before the new orbital solution can be confirmed.^[2]

[edit] Orbit and mass

47 Ursae Majoris c orbits further out than the previously-known planet 47 Ursae Majoris b, at a distance comparable to that of the outer asteroid belt in our solar system. It is slightly less massive than Jupiter. The orbital eccentricity is not well constrained, but it is likely to be low.^[3] The planet is located close to the 5:2 orbital resonance with 47 Ursae Majoris b, a similar configuration to Jupiter and Saturn in our solar system. In addition, the ratio of the masses of 47 Ursae Majoris b and c is similar to the mass ratio of Jupiter and Saturn.^[1]

A limitation of the radial velocity method used to detect 47 Ursae Majoris c is that only a lower limit on the planet's mass can be obtained. This lower limit is 0.792 times the mass of Jupiter. Stability considerations suggest that the true mass of the planet is likely to lie close to this lower limit.^[1]

[edit] Characteristics

Since 47 Ursae Majoris c was detected indirectly, properties such as its radius, composition and temperature are unknown. Based on its high mass, the planet is likely to be a gas giant with no solid surface.