HD 20781 d is an
extrasolar planet orbiting the
K-type main-sequence star HD 20781
HD 20781 is a star which is part of a wide binary system with HD 20782. The companion star has a very large angular separation of 252 arcsec, corresponding to 9080 AU at the distance of HD 20782. Both stars possess their own planetary ...
away in the southern
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Fornax. It was discovered in 2011 during a survey for southern exoplanets conducted with
HARPS[ using doppler spectroscopy, the radial velocity variations caused by the gravitational pull of the planet. Its existence was confirmed in another survey during 2017.][
]
Naming
This planet was initially reported in a 2011 preprint
In academic publishing, a preprint is a version of a scholarly or scientific paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal. The preprint may be available, often as a non-typeset versio ...
, which referred to it as HD 20781 b.[ However, the 2017 paper (published in a journal in 2019) that confirmed the planet designated it HD 20781 d, using the b designation for a different, shorter-period planet.][
]
Properties
Orbit
HD 20781 d takes only 29 days to orbit its host star, classifying it as a hot Neptune. However, its orbit is slightly eccentric, carrying it as close as and as far as .[ HD 20781 d is the second outermost planet in its system after ]HD 20781 e
HD 20781 e is a hot Neptune around the star HD 20781. The planet has a minimum mass of 14.03 Earth masses and it orbits with a semi-major axis of 0.3374 astronomical units and an orbital eccentricity of approximately 0.06. With the same composi ...
.
Characteristics
With a minimum mass 10.6 times that of Earth,[ it is probably a ]sub-Neptune
The term sub-Neptune can refer to a planet with smaller radius than Neptune even though it may have a larger mass or to a planet with a smaller mass than Neptune even though it may have a larger radius like a super-puff and both meanings can even ...
, a planet that is larger than Earth but smaller than Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
. Due to indirect detection, most of its properties can't be studied such as inclination, density, and temperature. Due to HD 20781 d's mass, it is estimated to be about 3 times larger than Earth.[
]
References
{{DEFAULTSORT:HD 20781 d
Exoplanets discovered in 2011
Fornax
Hot Neptunes
Exoplanets detected by radial velocity