38 Virginis b

38 Virginis b is a super-Jupiter exoplanet orbiting within the habitable zone of the star 38 Virginis about 107 light-years (32.7 parsecs, or nearly 7015101000000000000♠1.01×10¹⁵ km) from Earth in the constellation Virgo. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star.

Characteristics

Mass, radius and temperature

38 Virginis b is a super-Jupiter, an exoplanet that has a radius and mass larger than that of the planet Jupiter. It has a temperature of 258 K (−15 °C; 5 °F).^[3] It has a mass of 4.51 M_J^[2] and a likely radius of around 1.05 R_J based on its mass.

Host star

The planet orbits a (F-type) star named 38 Virginis. The star has a mass of 1.18 M_☉ and a radius of around 1.46 R_☉. It has a temperature of 6557 K and is about 1.9 billion years old. In comparison, the Sun is about 4.6 billion years old^[4] and has a temperature of 5778 K.^[5] The star is metal-rich, with a metallicity ([Fe/H]) of 0.16, or 117% the solar amount. Its luminosity (L_☉) is 3.48 times that of the Sun.^{[note 1]}

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 6.11. Therefore, 38 Virginis is on the edge of not being visible to the naked eye, but it can be clearly spotted with binoculars.

Orbit

38 Virginis b orbits its star every 825 days at a distance of 1.82 AU (close to Mars's orbital distance from the Sun, which is 1.53 AU). It likely receives 3% more sunlight as the Earth does from the Sun, due to its effective temperature being close to that of the Earth (in fact, only 3 degrees warmer).

Habitability

38 Virginis b resides in the habitable zone of the parent star. The exoplanet, with a mass of 4.51 M_J, is too massive to likely be rocky, and because of this the planet itself may not be habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life. However, such moons do not usually form around planets, they would likely have to be captured from afar; e.g, a protoplanet running astray.

For a stable orbit the ratio between the moon's orbital period P_s around its primary and that of the primary around its star P_p must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.^[6][7] Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or brown dwarf that orbits 1 AU from a Sun-like star.^[8] In the case of 38 Virginis b, the orbital period would have to be no greater than 80 days (a little over 2 months) in order to have a stable orbit.

Tidal effects could also allow the moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature^[9][10] and create a geodynamo effect which would give the satellite a strong magnetic field.^[11]

To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 M_⊕.^[12] One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's moon Ganymede has its own magnetosphere, even though its mass is only 0.025 M_⊕.^[8]

Discovery

The search for 38 Virginis b started when its host star was chosen an ideal target for a planet search using the radial velocity method (in which the gravitational pull of a planet on its star is measured by observing the resulting Doppler shift), as stellar activity would not overly mask or mimic Doppler spectroscopy measurements. It was also confirmed that 38 Virginis is neither a binary star nor a quickly rotating star, common false positives when searching for transiting planets. Analysis of the resulting data found that the radial velocity variations most likely indicated the existence of a planet.^[2] The net result was an estimate of a 4.52 M_J planetary companion orbiting the star at a distance of 1.82 AU with an eccentricity of 0.03.

The discovery of 38 Virginis b was reported in the online archive arXiv on August 29, 2016.

Notes

1. ↑ From , where is the luminosity, is the radius, is the effective surface temperature and is the Stefan–Boltzmann constant.

References

Coordinates: 12^h 53^m 11.3^s, −03° 33′ 11″

2016 in space
Spacecraft launches	ExoMars Trace Gas Orbiter (Mars orbiter) Schiaparelli EDM lander (Mars lander) Hitomi (X-ray observatory) OSIRIS-REx (mission to asteroid)
Selected NEOs	Asteroid close approaches 2013 TX68 252P/LINEAR 2016 EU85 (469219) 2016 HO3 2016 PQ
Planets	Exoplanets HD 19467 b 2MASS J2126-8140 BD+20594b Pr 0211-c TRAPPIST-1b TRAPPIST-1c TRAPPIST-1d Kepler-1229b Kepler-1520b Kepler-1638b Kepler-1647b Kepler-20g V830 Tau b Qatar-3b Qatar-4b Qatar-5b K2-33b HIP 41378 b HIP 41378 c HIP 41378 d HIP 41378 e HIP 41378 f HD 131399 Ab HD 164922 c KELT-11b K2-72b K2-72c K2-72d K2-72e Proxima Centauri b 38 Virginis b TW Hydrae b OGLE-2007-BLG-349(AB)b Gliese 536 b Solar Planet Nine (hypothesized) Rogue 2MASS J1119–1137
Space exploration	Akatsuki: entered Venus orbit Juno: entered Jupiter orbit Rosetta / Philae: end of mission to comet 67P
Miscellaneous	BOSS Great Wall GN-z11 Crater 2 2011 KT19 Virgo I
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