38 Virginis b

38 Virginis b is a super-Jupiter exoplanet orbiting within the habitable zone of the star 38 Virginis about 108.5 light-years (33.26 parsecs) 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.

38 Virginis b

Discovery
Discovery date	29 August 2016
Detection method	radial velocity
Orbital characteristics
Semi-major axis	1.82 (± 0.07) AU[1]
Eccentricity	0.03 (± 0.04)[1]
Orbital period (sidereal)	825.9 (± 6.2)[1] d
Time of periastron	2455490.2 ± 177.3[1]
Argument of periastron	−87.3 ± 77.7[1]
Star	38 Virginis
Physical characteristics
Mass	4.51 (± 0.5)[1] MJ

Characteristics

Mass

38 Virginis b is a super-Jupiter, an exoplanet that has a mass larger than that of the planet Jupiter. It has a minimum mass of 4.51 M_J.^[1]

Host star

Main article: 38 Virginis

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^[2] and has a temperature of 5778 K.^[3] 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 and habitability

38 Virginis b orbits its star every 825 days at a semi-major axis of 1.82 AU (this separation is comparable to Mars's semi-major axis, which is 1.53 AU). It likely receives as much sunlight as the Earth does from the Sun, due to its equilibrium temperature (assuming an albedo of 0.3) being only 3 degrees higher than that of Earth.^[4] Since 38 Virginis b is almost a gas giant, the habitability is instead considered for its hypothetical exomoons.^[5]

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.^[1] 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 ${\displaystyle {\begin{smallmatrix}L=4\pi R^{2}\sigma T_{\rm {eff}}^{4}\end{smallmatrix}}}$, where ${\displaystyle {\begin{smallmatrix}L\end{smallmatrix}}}$ is the luminosity, ${\displaystyle {\begin{smallmatrix}R\end{smallmatrix}}}$ is the radius, ${\displaystyle {\begin{smallmatrix}T_{\rm {eff}}\end{smallmatrix}}}$ is the effective surface temperature and ${\displaystyle {\begin{smallmatrix}\sigma \end{smallmatrix}}}$ is the Stefan–Boltzmann constant.

References

1. Borgniet, S.; et al. (2017). "Extrasolar planets and brown dwarfs around AF-type stars. IX. The HARPS southern sample". Astronomy and Astrophysics. 599. A57. arXiv:1608.08257. Bibcode:2017A&A...599A..57B. doi:10.1051/0004-6361/201628805.
2. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
3. Fraser Cain (September 15, 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
4. "38 Vir b". www.exoplanetkyoto.org. Retrieved 2024-09-21.
5. Cowing, Keith (2024-09-20). "The Habitability Of F-Type Star Systems". Astrobiology. Retrieved 2024-09-21.