61 Virginis

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61 Virginis
Observational Data
Astronomical designation HD 115617
HIP 64924
Right ascension 13h 18m 24.3s
Declination −18o 18′ 40.3″
Constellation Virgo
Type of object Star
Magnitude Apparent Mag: 4.74
Absolute Mag: 5.07
Distance from Earth 27.8 ly
Radial Velocity -8.2 km/s
Proper Motion RA: -1,069.90 mas/yr
Dec.: -1,063.78 mas/yr
Parallax 117.35 ± 0.69 mas

61 Virginis is a star located in the constellation of Virgo some 27.8 light years from Earth. It is visible to the unaided eye in sufficiently dark skies as a dim point of light with an apparent magnitude of 4.74. This otherwise nondescript star is noted for the recent discovery of three extrasolar planets in orbit.

Star System

61 Virginis has garnered interest because of its similarity to our Sun, and is considered one of the top 100 target stars for NASA's planned Terrestrial Planet Finder (TPF). This interest has increased in December 2009 when two "super-Earth" and one Neptune sized world was announced found orbiting the star.[1]

In addition to the planets, a large debris disk of icy dust lies in orbit around 61 Virginis either some 95 ±5 to 195 ± 10 AUs away if the dust are black bodies (emit no electromagnetic radiation), or 120 ±20 to 220 ±10 AUs away, if the dust emits radiation in the infrared.[2] This dust ring has open the hypothetical possibility of a fourth world far out from the star, shepherding the dust ring.

The Star

61 Virginis is a yellow-orange main sequence dwarf of spectral type G5-6 V. The star is a near twin of our own Sun, with 92 to 96 percent of its mass, and 94 to 98 percent of its diameter.[3] The star is also somewhat less luminous in comparison, with a total bolometric luminosity of 81 percent that of our Sun.[4] The star is considered "metal-rich" with a metallicity 1.1 times that of our Sun, based on the abundance of iron in the star.

61 Virginis b

61 Virginis b is the closest known planet to the star 61 Virginis, orbiting at a distance of only 0.050201 AU, with an orbital eccentricity of 0.12. At this distance, the world would complete an orbit in only 4.215 days. The planet has a mass 5.1 ±0.5 times of the Earth, classifying the world as a "super Earth". If the planet has a solid, terrestrial surface, it would be mostly molten rock.[5]

61 Virginis c

61 Virginis c is the second closest known planet to the star 61 Virginis. The world has a minimum mass 18.2 times that of the Earth making it likely a small gas giant not unlike Uranus or Neptune. The world orbits at a mean distance of 0.2175 AU with an eccentricity of 0.14. At this distance, the planet would orbit in only 38 days.[5]

61 Virginis d

61 Virginis d is the farthest known planet that orbits the star 61 Virginis. The planet has the greatest orbital eccentricity of the 61 Virginis system, with an eccentricity of 0.35. The mean distance of the world's orbit is 0.476 AU, a little less than one half of the size of the orbit of the Earth. The world is also the most massive known at 23 times the mass of the Earth. As such, the world is most likely a gas giant not unlike Uranus or Neptune.[5]

For an Earth-like planet to have liquid water on its surface, it would need to be centered around 0.9 AU from the star. Such a world would have an orbital period of roughly 317 days. Such a small world would be extremely difficult to detect with present technology.