Key parameters at a glance
- A radius of 1.21 Earth radii
- A mass of 1.93 Earth masses
- Surface gravity around 1.32 g
- An orbital period of 5.314 days
- Semi-major axis 0.0529 AU
- Distance from Earth 117.32 light-years
- Earth Similarity Index 0.939
- 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 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 systems in S type orbits, with a total of five known planets around both stars. This is the first known example of planets being found orbiting both components of a wide binary system. HD 20781 has no noticeable starspot activity.
Excerpted from Wikipedia · full article
3 siblings around HD 20781
HD 20781 b 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 this | Rocky Terrestrial | 1.21 | 1.93 | 5.314 | — | 2019 |
| HD 20781 c | Sub-Neptune | 2.17 | 5.33 | 13.891 | — | 2019 |
| HD 20781 d | Sub-Neptune | 3.25 | 10.61 | 29.158 | — | 2019 |
| HD 20781 e | Sub-Neptune | 3.83 | 14.03 | 85.507 | — | 2019 |
HD 20781 b Planet Profile
Physical Specs
Classification
Planet Type
Rocky Terrestrial
Discovery
Size rank in cohort
Rank by radius
#56of 570
top 9.6%
This planet
1.21R⊕
Rocky Terrestrial median
1.01R⊕
Nearest-size peers
| Metric | Earth | HD 20781 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 1.21 | 11.21 |
| Mass (M⊕) | 1.00 | 1.93 | 317.83 |
| Density (g/cm³) | 5.51 | 5.99 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.32 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Minimum mass (M sin i) | 1.930 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 Rocky Terrestrial cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 5.31 Earth days (1.5% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0529 AU.
Eq. Temperature
—
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.939
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
Kepler-415 b
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 1,730.2 ly
Kepler-80 f
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 1,205.0 ly
K2-228 b
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 422.2 ly
Kepler-326 d
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 1,590.6 ly
Kepler-1284 b
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 2,877.8 ly
Kepler-169 c
Rocky Terrestrial · K-type orange
Radius 1.21 R⊕ · 1,325.9 ly