Key parameters at a glance

A radius of 2.85 Earth radii
A mass of 8.50 Earth masses
Surface gravity around 1.05 g
An orbital period of 3.250 days
Semi-major axis 0.0410 AU
Distance from Earth 75.86 light-years
Earth Similarity Index 0.658
Travel time at Voyager 1 speed 1,337,854 years

HD 39855 b Planet Profile

Physical Specs

Radius

2.85 R⊕

Radius (Jupiter)

0.254 R♃

Mass

8.50 M⊕

Mass (Jupiter)

0.027 M♃

Density

2.02 g/cm³

Surface Gravity

1.05 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.658

HZ Position Unknown

Controversial No

Discovery

Year 2019

Method Radial Velocity

Facility Las Campanas Observatory

Telescope 6.5 m Magellan II Clay Telescope

Size rank in cohort

Rank by radius

#685of 1978

top 34.6%

This planet

2.85R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-358 c 2.85 R⊕ Kepler-288 c 2.85 R⊕ K2-199 c 2.85 R⊕

Metric	Earth	HD 39855 b	Jupiter
Radius (R⊕)	1.00	2.85	11.21
Mass (M⊕)	1.00	8.50	317.83
Density (g/cm³)	5.51	2.02	1.33
Surface Gravity (g)	1.00	1.05	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	8.500 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 39855

HIP

HIP 27922 A

TIC

TIC 160301040

Gaia DR2

Gaia DR2 2966316109264052096

Gaia DR3

Gaia DR3 2966316109264052096

System

HD 39855

Percentile among Sub-Neptune cohort

Radius 2.850 R⊕ · percentile 65 / cohort 1978

Mass 8.500 M⊕ · percentile 60 / cohort 1978

Orbital period 3.25 d · percentile 5 / cohort 1946

Distance 23.26 pc · percentile 5 / cohort 1975

ESI 0.658 · percentile 89 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

3.250 days

Semi-major axis

0.0410 AU

Eccentricity

0.140

Inclination

— °

Year Length

A year here lasts approximately 3.25 Earth days (0.9% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0410 AU.

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.658

0 = alien, 1 = Earth-identical

Discovery Paper

Primary reference

Feng et al. 2019

Instrument

Carnegie Planet Finder Spectrograph

Publication

2019-06

Observation locale

Ground

Discovery cohort

Planets confirmed in 2019 at Las Campanas Observatory (12 shown).

HIP 54373 b · Sub-Neptune HD 103949 b · Sub-Neptune HD 24085 b · Sub-Neptune HIP 54373 c · Sub-Neptune HIP 35173 b · Sub-Neptune HD 211970 b · Sub-Neptune HD 64114 b · Neptune-like HIP 71135 b · Neptune-like HD 206255 b · Neptune-like HD 21411 b · Neptune-like HD 8326 b · Neptune-like HD 102843 b · Gas Giant

Host System: HD 39855

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,576 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.745 R☉

Stellar Mass

0.870 M☉

Metallicity [Fe/H]

—

Extended Stellar Properties

Surface gravity (log g)

4.665 dex

Stellar density

3.131 g/cm³

Systemic radial velocity

42.58 km/s

Rotational v·sin i

3.00 km/s

Distance

23.26 parsec

Light-years 75.86 ly

V-band magnitude

7.51 mag

Voyager-speed travel 1,337,854 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

42.964 mas

Total Proper Motion

96.023 mas/yr

PM Right Ascension

92.85 mas/yr

PM Declination

-24.47 mas/yr

Galactic Cartesian (pc)

x = 0.023 · y = 0.941 · z = -0.337

Equatorial (J2000)

RA 88.62607° · Dec -19.70445°

Galactic ℓ, b

224.966° · -21.085°

Ecliptic λ, β

88.224° · -43.135°

HTM-20 index

-387805016