Key parameters at a glance

A radius of 4.49 Earth radii
A mass of 18.40 Earth masses
Surface gravity around 0.91 g
An orbital period of 40.870 days
Semi-major axis 0.2416 AU
Distance from Earth 187.82 light-years
Earth Similarity Index 0.509
Travel time at Voyager 1 speed 3,312,128 years

1 sibling around HD 5278

HD 5278 c shares its host star with 1 other confirmed planet. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
HD 5278 b	Sub-Neptune	2.45	7.80	14.339	943	2021
HD 5278 c this	Neptune-like	4.49	18.40	40.870	—	2021

HD 5278 c Planet Profile

Physical Specs

Radius

4.49 R⊕

Radius (Jupiter)

0.401 R♃

Mass

18.40 M⊕

Mass (Jupiter)

0.058 M♃

Density

1.12 g/cm³

Surface Gravity

0.91 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.509

HZ Position Unknown

Controversial No

Discovery

Year 2021

Method Radial Velocity

Facility Paranal Observatory

Telescope 8.2 m ESO VLT UT3 Melipal Telescope

Size rank in cohort

Rank by radius

#461of 574

top 80.1%

This planet

4.49R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

Kepler-1730 b 4.49 R⊕ K2-43 b 4.51 R⊕ Kepler-1769 b 4.47 R⊕

Metric	Earth	HD 5278 c	Jupiter
Radius (R⊕)	1.00	4.49	11.21
Mass (M⊕)	1.00	18.40	317.83
Density (g/cm³)	5.51	1.12	1.33
Surface Gravity (g)	1.00	0.91	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	18.400 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 5278

HIP

HIP 3911

TIC

TIC 263003176

Gaia DR2

Gaia DR2 4617759514501503616

Gaia DR3

Gaia DR3 4617759514501503616

System

HD 5278

Percentile among Neptune-like cohort

Radius 4.490 R⊕ · percentile 20 / cohort 574

Mass 18.400 M⊕ · percentile 23 / cohort 574

Orbital period 40.87 d · percentile 66 / cohort 524

Distance 57.58 pc · percentile 17 / cohort 572

ESI 0.509 · percentile 92 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

40.870 days

Semi-major axis

0.2416 AU

Eccentricity

0.070

Inclination

— °

Year Length

A year here lasts approximately 40.87 Earth days (11.2% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.2416 AU.

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.509

0 = alien, 1 = Earth-identical

Discovery Paper

Primary reference

Sozzetti et al. 2021

Instrument

ESPRESSO

Publication

2021-04

Observation locale

Ground

Discovery cohort

Planets confirmed in 2021 at Paranal Observatory (3 shown).

HD 22496 b · Sub-Neptune b Cen AB b · Gas Giant WASP-110 b · Gas Giant

Host System: HD 5278

Spectral Class

F-type yellow-white

Effective Temperature

6,203 K — hotter than the Sun (5,778 K)

Estimated Age

3.00 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

1.194 R☉

Stellar Mass

1.126 M☉

Metallicity [Fe/H]

-0.12

Extended Stellar Properties

Surface gravity (log g)

4.500 dex

Stellar density

0.932 g/cm³

Rotational v·sin i

4.10 km/s

Rotation period

16.80 days

Metallicity ratio

[Fe/H]

Distance

57.58 parsec

Light-years 187.82 ly

V-band magnitude

7.94 mag

Voyager-speed travel 3,312,128 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

17.337 mas

Total Proper Motion

142.716 mas/yr

PM Right Ascension

139.42 mas/yr

PM Declination

30.48 mas/yr

Galactic Cartesian (pc)

x = 0.106 · y = 0.024 · z = -0.994

Equatorial (J2000)

RA 12.54678° · Dec -83.74377°

Galactic ℓ, b

302.973° · -33.384°

Ecliptic λ, β

285.885° · -67.137°

HTM-20 index

2042616462