47 Ursae Majoris
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|47 Ursae Majoris|
|Right ascension (Epoch J2000)||10h 59m 27.97s|
|Declination (Epoch J2000)||+40° 25' 48.9"|
|Spectral type||G1 V|
|Distance from Sol||45.9 ± 0.2 ly|
|Other designations||Coyote, 47 UMa, BD+41°2147, FK5 1282, GC 15087, GCTP 2556.00, Gl 407, HD 95128, HIP 53721, HR 4277, LTT 12934, SAO 43557|
47 Ursae Majoris is G-type star, very similar to Sol, with at least two planets.
Wikipedia data dump (as of 29 January 2010) follows.
47 Ursae Majoris
47 Ursae Majoris, often abbreviated as 47 UMa, is a solar twin, yellow dwarf star approximately 46 light-years away from Earth in the constellation of Ursa Major. As of 2008, it has been confirmed that two extrasolar planets orbit the star. Because of this, 47 Ursae Majoris was listed as one of top 100 target stars for NASA's former Terrestrial Planet Finder mission.
Distance and visibility
47 Ursae Majoris is located fairly close to our solar system: according to astrometric measurements made by the Hipparcos astrometry satellite, the star exhibits a parallax of 71.11 milliarcseconds, corresponding to a distance of 14.1 parsecs. With an apparent magnitude of +5.03, it is visible to the naked eye under good conditions.
47 Ursae Majoris has a similar mass to that of our Sun. It is slightly more metal-rich than the Sun, having around 110% of the solar abundance of iron. With a spectral type of G1V, it is also slightly hotter than the Sun, at around 5,882 K. 47 Ursae Majoris has an absolute magnitude of +4.29, implying it has a visual luminosity around 60% greater than the Sun.
Like the Sun, 47 Ursae Majoris is on the main sequence, converting hydrogen to helium in its core by nuclear fusion. Based on its chromospheric activity, the star may be around 6,000 million years old, though evolutionary models suggest an older age of around 8,700 million years.
In 1996 an extrasolar planet was announced in orbit around 47 Ursae Majoris by Geoffrey Marcy and R. Paul Butler. The discovery was made by observing the change in the star's radial velocity as the planet's gravity pulled it around. The measurements were made by observing the Doppler shift of the star's spectrum. The planet, designated 47 Ursae Majoris b was the first long-period extrasolar planet discovered. Unlike the majority of known long-period extrasolar planets, 47 Ursae Majoris b has a low-eccentricity orbit. The planet is at least 2.62 times the mass of Jupiter and takes 1,095 days to orbit its star. If it were to be located in our solar system, it would lie between the orbits of Mars and Jupiter.
In 2001, preliminary astrometric measurements made by the Hipparcos probe suggest the orbit of 47 Ursae Majoris b is inclined at an angle of 63.1° to the plane of the sky. If these measurements are confirmed, this implies the planet's true mass is around 2.9 times that of Jupiter. However, subsequent analysis suggests that the Hipparcos measurements are not precise enough to accurately determine the orbits of substellar companions, and the inclination and true mass remain unknown.
A second planet, designated 47 Ursae Majoris c was announced in 2002 by Debra Fischer, Geoffrey Marcy, and R. Paul Butler. The discovery was made using the same radial velocity method used to detect the first planet. According to Fischer et al., the planet takes around 2,594 days to complete an orbit. This configuration is similar to the configuration of Jupiter and Saturn in our solar system, with the orbital ratio (close to 5:2), and mass ratio roughly similar.
Subsequent measurements failed to confirm the existence of the second planet, and it was noted that the dataset used to determine its existence left the planet's parameters "almost unconstrained". Analysis of a longer dataset spanning over 6,900 days suggests that while a second planet in the system is likely, periods near 2,500 days have a high false alarm probability, and the best fit model gives an orbital period of 7,586 days at a distance of 7.73 AU from the star. Nevertheless, the parameters of the second planet are still highly uncertain. On the other hand, the Catalog of Nearby Exoplanets gives a period of 2,190 days, which would put the planets close to a 2:1 ratio of orbital periods, though the reference for these parameters is uncertain: the original Fischer et al. paper is cited as a reference in spite of the fact that it gives different parameters, though this solution has been adopted by the Extrasolar Planets Encyclopaedia.
Simulations suggest that the inner part of the habitable zone of 47 Ursae Majoris could host a terrestrial planet on a stable orbit, though the outer regions of the habitable zone would be disrupted by the gravitational influence of the planet 47 Ursae Majoris b. However, the presence of a giant planet within 2.5 AU of the star may have disrupted planet formation in the inner system, and reduced the amount of water delivered to inner planets during accretion. This may mean any terrestrial planets orbiting in the habitable zone of 47 Ursae Majoris are likely to be small and dry. As of 2008, there have been two METI messages sent to 47 Ursae Majoris. Both were transmitted from Eurasia's largest radar — 70-meter (230-foot) Eupatoria Planetary Radar. The first message, the Teen Age Message, was sent on September 3, 2001, and it will arrive at 47 Ursae Majoris in July 2047. The second message, Cosmic Call 2, was sent on July 6, 2003, and it will arrive at 47 Ursae Majoris in May 2049.
47 Ursae Majoris b
|47 Ursae Majoris b|
|Orbit||2.14 AU from primary (Semimajor axis)|
|Year||1095.0 ± 2.9 days|
47 Ursae Majoris b is an extrasolar planet approximately 46 light-years away in the constellation of Ursa Major. The planet was discovered located in a long-period around the star 47 Ursae Majoris. The planet is currently the innermost known planet in its planetary system. 47 Ursae Majoris b was discovered in January 1996 and has a mass at least 2.62 times that of Jupiter.
Like the majority of known extrasolar planets, 47 Ursae Majoris b was discovered by detecting the changes in its star's radial velocity as the planet's gravity pulls the star around. This was achieved by observing the Doppler shift of the spectrum of 47 Ursae Majoris. After the discovery of the first extrasolar planet around a Sun-like star, 51 Pegasi b, astronomers Geoffrey Marcy and R. Paul Butler searched through their observational data for signs of extrasolar planets and soon discovered two: 47 Ursae Majoris b and 70 Virginis b. The discovery of 47 Ursae Majoris b was announced in 1996.
Orbit and mass
47 Ursae Majoris b orbits at a distance of 2.14 AU from its star, taking 1,095 days to complete a revolution. It was the first long-period planet around a main sequence star to be discovered. Unlike the majority of known long-period extrasolar planets, the eccentricity of the orbit of 47 Ursae Majoris b is low.
A limitation of the radial velocity method used to detect 47 Ursae Majoris b is that only a lower limit on the planet's mass can be obtained. Preliminary astrometric measurements made by the Hipparcos satellite suggest the planet's orbit is inclined at an angle of 63.1° to the plane of the sky, which would imply a true mass 12% greater than the lower limit determined by radial velocity measurements. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterise the orbits of substellar companions, and the true inclination of the orbit (and hence the true mass) are regarded as unknown.
Given the planet's high mass, it is likely that 47 Ursae Majoris 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. Due to its mass it is likely to have a surface gravity 6–8 times that of Earth. Assuming a composition similar to that of Jupiter and an environment close to chemical equilibrium, the upper atmosphere of the planet is expected to contain water clouds, as opposed to the ammonia clouds typical of Jupiter.
While 47 Ursae Majoris b lies outside its star's habitable zone, its gravitational influence would disrupt the orbit of planets in the outer part of the habitable zone. In addition, it may have disrupted the formation of terrestrial planets and reduced the delivery of water to any inner planets in the system. Therefore planets located in the habitable zone of 47 Ursae Majoris are likely to be small and dry.
It has been theorized that light reflections and infrared emissions from 47 UMa b, along with tidal influence, could warm any moons in orbit around it to be habitable, despite the planet being outside the normally accepted habitable zone.
47 Ursae Majoris c
|47 Ursae Majoris c|
|Orbit||3.39 AU from primary (Semimajor axis)|
|Year||2190 ± 460 days|
47 Ursae Majoris c is an extrasolar planet approximately 46 light-years away in the constellation of Ursa Major. The planet was discovered located in a long-period around the star 47 Ursae Majoris. It is currently the outermost known planet in its planetary system. Its orbit lasts 6 years and the planet has a mass at least 0.46 times that of Jupiter.
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 in 2001, 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 explained by assuming that 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 suggested that the periodicity could not be explained by stellar activity, making the planet interpretation more likely. The planet was announced in 2002.
Further measurements of 47 Ursae Majoris failed to detect the planet, calling its existence into question. Furthermore, it was noted that the data used to determine its existence left the planet's parameters "almost unconstrained". A more recent study with datasets spanning over 6,900 days came to the conclusion that while the existence of a second planet in the system is likely, periods around 2,500 days have high false-alarm probabilities. The best solution gives a period of 7,586 days (almost 21 years), which would place the planet at 7.73 AU from the star. The parameters are still highly uncertain. The Catalog of Nearby Exoplanets gives an orbital period of 2,190 days, however the reference it uses is Fischer et al. (2002), which does not support this assertion. Nevertheless, these parameters have also been adopted by the Extrasolar Planets Encyclopaedia.
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.