61 Virginis

Steven Vogt,
UCSC,




Larger map.




61 Virginis
is located
southwest of
the bright
type-B binary
Spica, Alpha
Virginis, in
Constellation
Virgo (more).

On December 14, 2009, a team of astronomers announced the discovery of one super-Earth and two Neptune-class planets (with at least 5, 18, and 24 Earth-masses, respectively) in moderately circular, inner orbits around 61 Virginis with periods of 4.2, 38.0, and 124.0 days (U.C. Santa Cruz news release; AAO press release; Keck press release; the Lick-Carnegie Exoplanet Survey Team's "Systemic Console;" and Vogt et al, 2009 -- more below). The super-Earth is one of the first two found around a spectral type G star, like our Sun, Sol. According to astronomers working with the Spitzer Space Telescope, a thick belt of dust (that is probably being generated by collisions between Edgeworth-Kuiper-Belt-type, icy objects) lies some 96 to 195 AUs out from the star (Bryden et al, 2009; Tanner et al, 2009, see HD 115617; and Vogt et al, 2009 -- more below).

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	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Earths)	Diameter (Earths)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
61 Vir	0.0	...	...	...	314,000	105	...	...	1.1
Planet "b"	0.050	0.011	0.12	?	=>5.1	>1	...	...	...
Planet "c"	0.218	0.104	0.14	?	=>18.2	>1	...	...	...
Planet "d"	0.476	0.340	0.35	?	=>24.0	>1	...	...	...
Inner H.Z. Edge	0.764	0.685	0	?	...	...	...	...	...
Outer H.Z. Edge	1.520	1.923	0	?	...	...	...	...	...
Inner Debris Orbit	96	965	0	?	...	...	...	...	...
Outer Debris Orbit	195	1,793	0	?	...	...	...	...	...

The Star

61 Virginis is a yellow-orange main sequence dwarf of spectral and luminosity type G5-6 V, with about 92 to 96 percent of Sol's mass (95 percent using the isochrone mass estimate of Valenti and Fischer, 2005; and NASA Star and Exoplanet Database, based on David F. Gray, 1992), 94 to 98 percent of its diameter (96 percent for Valenti and Fischer, 2005; Johnson and Wright, 1983, page 677; and NASA Star and Exoplanet Database, derived from the exponential formula of Kenneth R. Lang, 1980), and around 78 percent of its visual luminosity and nearly 81 percent of its theoretical bolometric luminosity, with infrared radiation (Sousa et al, 2008; Valenti and Fischer, 2005; NASA Star and Exoplanet Database, based on Kenneth R. Lang, 1980). The star may be as much as 1.1 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (NASA Star and Exoplanet Database from Valenti and Fischer, 2005; and Cayrel de Strobel et al, 1991, page 295). It appears to be "an old, inactive star" of 6.3 to 9.0 billion years in age (Vogt et al, 2009; Takeda et al, 2007; and Valenti and Fischer, 2005). Over 16 years of photometric observations indicate that 61 Virginis is photometically stable (Vogt et al, 2009). Useful star catalogue numbers for the star include: 61 Vir, HR 5019, Gl 506, Hip 64924, HD 115617, BD-17 3813, SAO 157844, FK5 1345, LHS 349, LTT 5111, LPM 467, LFT 990, and GC 18007.

Sky View, NASA



Larger false-color image.



61 Virginis is a little
smaller, less massive,
and dimmer than our
Sun, Sol.

Habitable Zone

According to one type of model calculations performed for the NASA Star and Exoplanet Database, the inner edge of 61 Vir's habitable zone should be located around 0.76 AU from the star, while the outer edge edge lies around 1.52 AUs. Hence, all of the known planets of 61 vir orbit withing the star's habitable zone's inner edge and so are presumed to be too hot to have liquid water on their surface. Astronomers are hoping that someday they will be able to use NASA's indefinitely postponed Terrestrial Planet Finder (TPF) and the ESA's Darwin similarly postponed groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around 61 Virginis. As proposed, the TPF will include two complementary observatory groups: a visible-light coronagraph; and a "formation-flying" infrared interferometer, while Darwin would launch a flotilla of three mid-infrared telescopes and a fourth communications hub. (See a larger animation of the planetary orbits, dust disk, and potentially habitable zone around 61 Virginis.)

Debris Disk

Planetary System

As of December 14, 2009, the 61 Virginis system is known to have one super-Earth and two Neptune-class planets, as well as a circumstellar debris disk. Prior to 2009, small but significant variations in radial velocity had been detected which may have been caused by a substellar companion of one to nine Jupiter-masses with an orbital period of 50 years of less (Campbell et al, 1988, pages 904, 906, and 919). A subsequent radial velocity study also failed to detect a brown dwarf sized companion (with 20 to 80 times the mass of Jupiter) within 10 AUs of 61 Virginis (Murdoch et al, 1993). A few years later, even a brown dwarf or Jupiter- or Saturn-class planet in a inner orbit was discounted with further observations (Cumming et al, 1999).

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