47 Ursae Majoris
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Planetary System Summary
47 Ursae Majoris (UMa) is located about 45.9 light-years from Sol. It lies in the southcentral part (10:59:28.0+40:25:48.9, ICRS 2000.0) of Constellation Ursa Major, the Great Bear -- southeast of Omega UMa, southwest of Psi UMa, northeast of 46 UMa, and northwest of 55 UMa. with 47 UMa labeled). In 1996, astronomers announced the discovery of a Jupiter-like planet around this Sun-like star (Butler and Marcy, 1996. with indications of an even larger planet in an outer orbit. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)The Star
47 UMa is a yellow-orange main sequence dwarf star of spectral and luminosity type G0-1 V, with about 1.03 times the mass of Sol (47 UMa, 1.26 times its diameter. Useful catalogue numbers and designations for the star include: 47 UMa, HR 4277, Gl 407, Hip 53721, HD 95128, BD+41 2147, SAO 43557, FK5 1282, and LTT 12934.Stable Orbits in the Habitable Zone
Recently, astronomers at the University of Texas at Arlington performed refined calculations to determine that the habitable zone around 47 Ursae Majoris, where an inner rocky planet (with suitable mass and atmospheric gas composition and density) can have liquid water on its surface, lies between 1.05 and 1.83 AUs of the star. They found that the development of an Earth-like planet in the inner portion of this zone may survive disruption from the development of known planetary candidates planet b and c. If a small, rocky planet can develop without the interference of planet b, then stable orbits appear to be possible in the inner portion of the habitable zone Subsequent analysis suggests that the habitability of such an inner rocky planet would be boosted if the star was "relatively young" at six or less billion years old and has a "relatively small stellar luminosity". |
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47 Ursae Majoris B
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47 Ursae Majoris B Statistics
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47 Ursae Majoris b, like 70 Virginis b, is a very promising world. It too lies with in the right distance range from its sun for liquid water to exist, lending more hope that one day Earth-like worlds may be detected at habitable orbits around sun-like stars. But unlike hot 70 Virginis b, 47 Ursae Majoris b is a cooler place. Twice the distance from 47 Ursae Majoris than Earth is from our own sun, 47 Ursae Majoris b is colder than Mars. |
Like 70 Virginis b and Jupiter, 47 Ursae Majoris b is not likely to have an abundance of water in the atmosphere, although this is not a certainty. But frozen water could be found on the moons of 47 Ursae Majoris b. In the case of hot 70 Virginis b, the moons are entirely rocky, like Mars or Mercury. Jupiter's moons, significately further out from the sun, have rocky cores but substantial mantles of water ice. Farther out still, the moons of Saturn are probably all or mostly ice, with surfaces of frozen methane. The more distant a non-jovian world is from its sun, the more ice and the less rock it contains.
So the moons of 47 Ursae Majoris b, not as scalded as those of 70 Virginis, and not as frozen as those of Jupiter, exist at a medium. They probably have rocky cores and mantles, but their surfaces may be thick with ice. Larger more tectonically active moons will have channels and valleys where rivers of water were melted by geothermic heat and then frozen again after the heat disapated. Meteoric impacts would also melt the ice into running streams of water. Such features can be seen on Mars, where volcanic eruptions heated subsurface ice into rivers which cut channels into the terrain until the water froze once more.
One very interesting possibility is that one of the larger, tectonically active moons may hide a global ocean under a thin crust of ice. Heated by volcanism and ocean floor fumerals, such dark oceans may be warm enough for life to thrive. There is actually support for this possibility in our own solar system. Many astronomers speculate that the Jovian moon Europa itself has a deep ocean of water, headed by tidal fiction caused by it's close orbit to Jupiter, underneath its icy surface. Deep below the frozen surface of a moon of 47 Ursae Majoris b may be seas of water teeming with swimming creatures which have never seen sunlight.
47 Ursae Majoris C
47 Ursae Majoris C Statistics
| Object Type: | Jupiter-twin |
| Parent Star: | 47 Ursae Majoris (G0 V) |
| Discovery Status: | Confirmed |
| Mass : | 0.76 Jupiters |
| Mean Distance: | 3.73 AU |
| Orbital Period: | 2594 + 90 Days |
| Eccentricity: | 0.1 + 0.1 |
| Planet Appearance: | White ammonia and water ice clouds, brown hydrocarbon stains |
| Estimated Radius: | 0.975 Jupiters |
| Estimated Mean Temp: | 128 Kelvin |
| Mean Angular Star Size: | 0.149 Degrees |
| Year Discovered: | 2001 |
| Detection Method: | Doppler Spectroscopy |
| Discovered By: | D. Fischer et al |
Planetary Orbits Around 47 Ursae Majoris
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