47 Ursae Majoris

47 Ursae Majoris (abbreviated 47 UMa) is a 5th magnitude yellow dwarf star in the constellation of Ursa Major. Its spectral type, G1 V, is similar to our Sun. The star is relatively nearby, distance being only 44 light years. It is visible to the unaided eye under good conditions.

It was one of the first stars known to possess extrasolar planets. It currently has two known planets, designated as 47 Ursae Majoris b and c.

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47 Ursae Majoris b

After the discovery of the first extrasolar planet around a Sun-like star, 51 Pegasi b, astronomers Geoffrey Marcy and Paul Butler searched through their observational data for extrasolar planets and soon discovered two, 47 Ursae Majoris b and 70 Virginis b. Had they known that many planets orbit close their parent stars, they would have been the first extrasolar planet discoverers.

But 47 Ursae Majoris b is different. Like others, it is a massive gas giant, being about 2.5 times as massive as Jupiter. However, its distance from the star is larger than most, little more than that of Mars from our Sun. And, unlike the "eccentric Jupiters", the orbit of the planet is almost circular as is the case with the giant planets in our Solar system.

Unfortunately, the moons of the planet, if it has any, are likely too cold to support any life unless they have subsurface oceans like Jupiter's moon Europa. On the other hand, the planet is still too close to its parent star as its gravitational influence may have prevented formation of any Earth-like planets in the system.

47 Ursae Majoris c

**47 Ursae Majoris c**
Orbital Elements
Semi-Major Axis (a)	3.73 AU
Eccentricity (e)	0.1 ± 0.1
Orbital Period (P)	7 y 39 ± 90 d
Inclination (i)	?°
Longitude of Periastron (ϖ)	127°
Time of Periastron (τ)	2,451,363.5 JD
Physical Characteristics
Mass	>0.76 M_J
Radius	? R_J
Density	? kg/m³
Temperature	? K
Discovery
Discoverers	Fischer, Butler, Marcy, et al.
Discovery Date	2002

The second planet, 47 Ursae Majoris c, orbits further out than planet b, about the distance of the outer asteroid belt in our Solar system. It is slightly less massive than Jupiter, and it too has a fairly circular orbit.

The planetary system of 47 Ursae Majoris shares other similarities with our Solar system, too: the ratio between the masses of b and c is 3.34 (3.32 between Jupiter and Saturn), and the ratio between orbital distances of the planets is 0.560 (0.545). Whether this is just coincidence or has any deeper meaning has not yet been figured out.

References

"47 UMA B." SIMBAD. Accessed on April 17, 2005.
"47 UMA C." SIMBAD. Accessed on April 17, 2005.
"Notes for 47 UMa." The Extrasolar Planets Encyclopaedia. Accessed on April 17, 2005.

External links