Key parameters at a glance
- A radius of 3.25 Earth radii
- A mass of 10.61 Earth masses
- Surface gravity around 1.00 g
- An orbital period of 29.158 days
- Semi-major axis 0.1647 AU
- Distance from Earth 117.32 light-years
- Earth Similarity Index 0.612
- Travel time at Voyager 1 speed 2,068,995 years
- Almost certainly tidally locked to its host star given the close orbit
Context from the literature
HD 20781 d is an extrasolar planet orbiting the K-type main-sequence star HD 20781 117 light years away in the southern constellation 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.
Excerpted from Wikipedia · full article
3 siblings around HD 20781
HD 20781 d shares its host star with 3 other confirmed planets. Side-by-side measurements below.
| Planet | Type | Radius (R⊕) | Mass (M⊕) | Period (d) | Eq. T (K) | Year |
|---|---|---|---|---|---|---|
| HD 20781 b | Rocky Terrestrial | 1.21 | 1.93 | 5.314 | — | 2019 |
| HD 20781 c | Sub-Neptune | 2.17 | 5.33 | 13.891 | — | 2019 |
| HD 20781 d this | Sub-Neptune | 3.25 | 10.61 | 29.158 | — | 2019 |
| HD 20781 e | Sub-Neptune | 3.83 | 14.03 | 85.507 | — | 2019 |
HD 20781 d Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#312of 1978
top 15.7%
This planet
3.25R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | HD 20781 d | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 3.25 | 11.21 |
| Mass (M⊕) | 1.00 | 10.61 | 317.83 |
| Density (g/cm³) | 5.51 | 1.70 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.00 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Minimum mass (M sin i) | 10.610 M⊕ | Lower bound from radial-velocity fitting. |
Star Catalogue Identifiers
HD
HD 20781
HIP
HIP 15526
TIC
TIC 144503312
Gaia DR2
Gaia DR2 5060105892897388288
Gaia DR3
Gaia DR3 5060105897197110144
System
HD 20782
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 29.16 Earth days (8.0% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1647 AU.
Eq. Temperature
—
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.612
0 = alien, 1 = Earth-identical
Insufficient insolation data. Close-orbiting tidally-locked around a cool host.
Discovery Paper
Primary reference
Udry et al. 2019Instrument
HARPS Spectrograph
Publication
2019-02
Observation locale
Ground
Discovery cohort
Planets confirmed in 2019 at La Silla Observatory (12 shown).
Host System: HD 20781
Spectral Class
K-type orange
Effective Temperature
5,256 K — cooler than the Sun (5,778 K)
Estimated Age
—
Stellar Radius
0.834 R☉
Stellar Mass
0.700 M☉
Metallicity [Fe/H]
-0.11
Extended Stellar Properties
Surface gravity (log g)
4.370 dex
Stellar density
1.962 g/cm³
Systemic radial velocity
40.31 km/s
Rotational v·sin i
1.10 km/s
Rotation period
46.80 days
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 7 bands
Astrometric Data
Parallax
27.771 mas
Total Proper Motion
355.159 mas/yr
PM Right Ascension
348.85 mas/yr
PM Declination
-66.66 mas/yr
Galactic Cartesian (pc)
x = 0.563 · y = 0.672 · z = -0.482
Equatorial (J2000)
RA 50.01398° · Dec -28.78412°
Galactic ℓ, b
224.673° · -57.272°
Ecliptic λ, β
37.008° · -45.145°
HTM-20 index
-935964729
Similar Worlds
TOI-2093 b
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HD 48948 d
Sub-Neptune · K-type orange
Radius 3.24 R⊕ · 55.1 ly
Kepler-287 c
Sub-Neptune · K-type orange
Radius 3.26 R⊕ · 2,726.2 ly
K2-348 b
Sub-Neptune · K-type orange
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Kepler-742 b
Sub-Neptune · K-type orange
Radius 3.24 R⊕ · 1,595.7 ly
Kepler-278 c
Sub-Neptune · K-type orange
Radius 3.27 R⊕ · 1,445.0 ly