.png) An artist's impression of HD 20781 d orbiting its host star. | |
| Discovery[1] | |
|---|---|
| Discovered by | Mayor et al. |
| Discovery site | La Silla Observatory[2] |
| Discovery date | 2011 |
| Doppler spectroscopy (HARPS) | |
| Orbital characteristics[3] | |
| Periastron | 0.15 AU |
| Apoastron | 0.18 AU |
| 0.1647+0.0076 −0.0083 AU | |
| Eccentricity | 0.11+0.05 −0.06 |
| 29.1580+0.0102 −0.0100 d | |
| 2,455,511.3258+2.4394 −2.4382 JD | |
| 60.99°+30.79° −30.03° | |
| Semi-amplitude | 2.82+0.17 −0.16 m/s |
| Physical characteristics | |
| ~3.18 R🜨 (estimate)[2] | |
| Mass | ≥10.61+1.20 −1.19 M🜨[3] |
HD 20781 d is anextrasolar planet orbiting theK-type main-sequence starHD 20781117 light years away in the southernconstellationFornax. It was discovered in 2011 during a survey for southern exoplanets conducted withHARPS[1] usingdoppler spectroscopy, the radial velocity variations caused by the gravitational pull of the planet. Its existence was confirmed in another survey during 2017.[3]
This planet was initially reported in a 2011preprint, which referred to it as HD 20781 b.[1] 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.[3]
HD 20781 d takes only 29days to orbit its host star, classifying it as ahot Neptune. However, its orbit is slightly eccentric, carrying it as close as0.15 AU and as far as0.18 AU.[3] HD 20781 d is the second outermost planet in its system afterHD 20781 e.
With aminimum mass 10.6 times that ofEarth,[3] it is probably asub-Neptune, a planet that is larger thanEarth but smaller thanNeptune. Due to indirect detection, most of its properties can't be studied such asinclination, density, and temperature. Due to HD 20781 d's mass, it is estimated to be about 3 times larger thanEarth.[2]
