Key parameters at a glance

A radius of 2.16 Earth radii
A mass of 5.30 Earth masses
Surface gravity around 1.14 g
An orbital period of 33.747 days
Semi-major axis 0.1300 AU
Distance from Earth 40.70 light-years
Earth Similarity Index 0.757
Travel time at Voyager 1 speed 717,664 years
Almost certainly tidally locked to its host star given the close orbit

1 sibling around 55 Cnc B

55 Cnc B 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
55 Cnc B b	Super-Earth	1.69	3.50	6.799	—	2025
55 Cnc B c this	Sub-Neptune	2.16	5.30	33.747	—	2025

55 Cnc B c Planet Profile

Physical Specs

Radius

2.16 R⊕

Radius (Jupiter)

0.193 R♃

Mass

5.30 M⊕

Mass (Jupiter)

0.017 M♃

Density

2.89 g/cm³

Surface Gravity

1.14 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.757

HZ Position Unknown

Controversial No

Discovery

Year 2025

Method Radial Velocity

Facility Mauna Kea Observatory

Telescope 3.58 m Canada-France-Hawaii Telescope (CFHT)

Size rank in cohort

Rank by radius

#1731of 1978

top 87.5%

This planet

2.16R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-291 b 2.16 R⊕ Kepler-142 d 2.16 R⊕ Kepler-308 c 2.16 R⊕

Metric	Earth	55 Cnc B c	Jupiter
Radius (R⊕)	1.00	2.16	11.21
Mass (M⊕)	1.00	5.30	317.83
Density (g/cm³)	5.51	2.89	1.33
Surface Gravity (g)	1.00	1.14	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	5.300 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

TIC

TIC 332064684

Gaia DR2

Gaia DR2 704966762213039488

Gaia DR3

Gaia DR3 704966762213039488

System

55 Cnc

Percentile among Sub-Neptune cohort

Radius 2.160 R⊕ · percentile 12 / cohort 1978

Mass 5.300 M⊕ · percentile 13 / cohort 1978

Orbital period 33.75 d · percentile 76 / cohort 1946

Distance 12.48 pc · percentile 2 / cohort 1975

ESI 0.757 · percentile 97 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

33.747 days

Semi-major axis

0.1300 AU

Eccentricity

0.000

Inclination

— °

Year Length

A year here lasts approximately 33.75 Earth days (9.2% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1300 AU.

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.757

0 = alien, 1 = Earth-identical

Insufficient insolation data. Close-orbiting tidally-locked around a cool host.

Discovery Paper

Primary reference

Moutou et al. 2025

Instrument

SPIRou

Publication

2025-10

Observation locale

Ground

Discovery cohort

Planets confirmed in 2025 at Mauna Kea Observatory (2 shown).

55 Cnc B b · Super-Earth Gl 410 b · Sub-Neptune

Host System: 55 Cnc B

Spectral Class

M-type red dwarf

Effective Temperature

3,286 K — cooler than the Sun (5,778 K)

Estimated Age

10.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.274 R☉

Stellar Mass

0.260 M☉

Metallicity [Fe/H]

0.16

Extended Stellar Properties

Surface gravity (log g)

4.860 dex

Stellar density

15.368 g/cm³

Rotational v·sin i

1.29 km/s

Rotation period

92.00 days

Metallicity ratio

[M/H]

Distance

12.48 parsec

Light-years 40.70 ly

V-band magnitude

13.15 mag

Voyager-speed travel 717,664 yr

Multi-band Host Photometry — 7 bands

Astrometric Data

Parallax

80.117 mas

Total Proper Motion

539.883 mas/yr

PM Right Ascension

-481.20 mas/yr

PM Declination

-244.78 mas/yr

Galactic Cartesian (pc)

x = -0.602 · y = 0.642 · z = 0.474

Equatorial (J2000)

RA 133.16791° · Dec 28.31529°

Galactic ℓ, b

196.819° · 37.711°

Ecliptic λ, β

127.749° · 10.357°

HTM-20 index

568990408