Key parameters at a glance

A radius of 2.45 Earth radii
A mass of 7.80 Earth masses
Surface gravity around 1.30 g
An orbital period of 14.339 days
Semi-major axis 0.1202 AU
Equilibrium temperature 943 K (670 °C)
Distance from Earth 187.82 light-years
Earth Similarity Index 0.274
Travel time at Voyager 1 speed 3,312,128 years

1 sibling around HD 5278

HD 5278 b 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 this	Sub-Neptune	2.45	7.80	14.339	943	2021
HD 5278 c	Neptune-like	4.49	18.40	40.870	—	2021

HD 5278 b Planet Profile

Physical Specs

Radius

2.45 R⊕

Radius (Jupiter)

0.219 R♃

Mass

7.80 M⊕

Mass (Jupiter)

0.025 M♃

Density

2.90 g/cm³

Surface Gravity

1.30 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.274

HZ Position Inner

Controversial No

Discovery

Year 2021

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#1260of 1978

top 63.7%

This planet

2.45R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-1176 b 2.45 R⊕ TOI-2274 b 2.45 R⊕ Kepler-243 b 2.45 R⊕

Metric	Earth	HD 5278 b	Jupiter
Radius (R⊕)	1.00	2.45	11.21
Mass (M⊕)	1.00	7.80	317.83
Density (g/cm³)	5.51	2.90	1.33
Surface Gravity (g)	1.00	1.30	2.53
Insolation (S⊕)	1.00	132.00	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	7.800 M⊕	Direct mass measurement (not derived).

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 Sub-Neptune cohort

Radius 2.450 R⊕ · percentile 36 / cohort 1978

Mass 7.800 M⊕ · percentile 52 / cohort 1978

Orbital period 14.34 d · percentile 49 / cohort 1946

Distance 57.58 pc · percentile 13 / cohort 1975

ESI 0.274 · percentile 22 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

14.339 days

Semi-major axis

0.1202 AU

Eccentricity

0.080

Inclination

89.27 °

Year Length

A year here lasts approximately 14.34 Earth days (3.9% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1202 AU.

Transit Fingerprint

Depth

0.039 %

Duration

4.800 h

Impact parameter b

0.270

Rp / R★

0.018740

Transit midpoint (BJD)

2,458,680.6993

Photometric dip

Transit produces a flux drop of 393 ppm lasting ≈ 4.80 h.

Extended Orbital Architecture

Planet / star radius ratio

0.018740

Semi-major axis / stellar radius

22.400

Impact parameter (b)

0.270

RV semi-amplitude (K)

1.930 m/s

Transit mid-time (BJD)

2,458,680.6993

Long. of periastron (ω)

135.00°

Angular separation (arcsec)

2.09000

Eq. Temperature

943K

(670 °C)

Insolation (S⊕)

132.00

Earth = 1.00

Earth Similarity (ESI)

0.274

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Radial velocity

Stellar wobble has been measured spectroscopically.

Discovery Paper

Primary reference

Sozzetti et al. 2021

Instrument

TESS CCD Array

Publication

2021-04

Observation locale

Space

Discovery cohort

Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

TOI-2257 b · Sub-Neptune TOI-2285 b · Super-Earth TOI-1231 b · Sub-Neptune AU Mic c · Sub-Neptune LHS 1678 c · Rocky Terrestrial LHS 1478 b · Rocky Terrestrial TOI-2406 b · Sub-Neptune HD 207897 b · Sub-Neptune TOI-269 b · Sub-Neptune TIC 172900988 b · Gas Giant TOI-178 g · Sub-Neptune TOI-2076 d · Sub-Neptune

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