Key parameters at a glance
- A radius of 2.17 Earth radii
- A mass of 5.33 Earth masses
- Surface gravity around 1.13 g
- An orbital period of 13.891 days
- Semi-major axis 0.1004 AU
- Distance from Earth 117.32 light-years
- Earth Similarity Index 0.755
- 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 c 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 this | 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 c Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1720of 1978
top 86.9%
This planet
2.17R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | HD 20781 c | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.17 | 11.21 |
| Mass (M⊕) | 1.00 | 5.33 | 317.83 |
| Density (g/cm³) | 5.51 | 2.87 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.13 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Minimum mass (M sin i) | 5.330 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 13.89 Earth days (3.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1004 AU.
Eq. Temperature
—
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.755
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-1009 b
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 1,157.9 ly
Kepler-1329 b
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 1,917.9 ly
Kepler-304 c
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 1,417.7 ly
Kepler-102 e
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 351.6 ly
Kepler-1653 b
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 2,462.5 ly
TOI-904 c
Sub-Neptune · K-type orange
Radius 2.17 R⊕ · 150.3 ly