Key parameters at a glance

A radius of 8.51 Earth radii
A mass of 54.47 Earth masses
Surface gravity around 0.75 g
An orbital period of 44.394 days
Semi-major axis 0.2470 AU
Distance from Earth 41.05 light-years
Earth Similarity Index 0.340
Travel time at Voyager 1 speed 723,888 years

4 siblings around 55 Cnc

55 Cnc c shares its host star with 4 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
55 Cnc e	Super-Earth	1.88	7.99	0.737	1,958	2004
55 Cnc b	Gas Giant	13.90	263.98	14.652	700	1996
55 Cnc c this	Neptune-like	8.51	54.47	44.394	—	2004
55 Cnc f	Neptune-like	7.59	44.81	260.580	—	2007
55 Cnc d	Gas Giant	13.00	1,232.49	4,799.000	—	2002

55 Cnc c Planet Profile

Physical Specs

Radius

8.51 R⊕

Radius (Jupiter)

0.760 R♃

Mass

54.47 M⊕

Mass (Jupiter)

0.171 M♃

Density

0.49 g/cm³

Surface Gravity

0.75 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.340

HZ Position Unknown

Controversial No

Discovery

Year 2004

Method Radial Velocity

Facility McDonald Observatory

Telescope 9.2 m Hobby-Eberly Telescope

Size rank in cohort

Rank by radius

#122of 574

top 21.1%

This planet

8.51R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

Kepler-719 b 8.52 R⊕ TOI-5786 b 8.54 R⊕ TOI-4994 b 8.54 R⊕

Metric	Earth	55 Cnc c	Jupiter
Radius (R⊕)	1.00	8.51	11.21
Mass (M⊕)	1.00	54.47	317.83
Density (g/cm³)	5.51	0.49	1.33
Surface Gravity (g)	1.00	0.75	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	54.474 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	56.600 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 75732

HIP

HIP 43587

TIC

TIC 332064670

Gaia DR2

Gaia DR2 704967037090946688

Gaia DR3

Gaia DR3 704967037090946688

System

55 Cnc

Percentile among Neptune-like cohort

Radius 8.510 R⊕ · percentile 79 / cohort 574

Mass 54.474 M⊕ · percentile 75 / cohort 574

Orbital period 44.39 d · percentile 68 / cohort 524

Distance 12.59 pc · percentile 3 / cohort 572

ESI 0.340 · percentile 61 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

44.394 days

Semi-major axis

0.2470 AU

Eccentricity

0.088

Inclination

89.73 °

Year Length

A year here lasts approximately 44.39 Earth days (12.2% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.2470 AU.

Extended Orbital Architecture

RV semi-amplitude (K)

10.170 m/s

Transit mid-time (BJD)

2,455,491.2300

Long. of periastron (ω)

31.00°

Angular separation (arcsec)

19.60000

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.340

0 = alien, 1 = Earth-identical

Discovery Paper

Primary reference

Mcarthur et al. 2004

Instrument

High Resolution Spectrograph

Publication

2004-10

Observation locale

Ground

Discovery cohort

Planets confirmed in 2004 at McDonald Observatory (2 shown).

HD 37605 b · Gas Giant 55 Cnc e · Super-Earth

Host System: 55 Cnc

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,198 K — cooler than the Sun (5,778 K)

Estimated Age

10.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.980 R☉

Stellar Mass

1.015 M☉

Metallicity [Fe/H]

0.39

Extended Stellar Properties

Surface gravity (log g)

4.300 dex

Stellar density

1.521 g/cm³

Systemic radial velocity

27.41 km/s

Rotational v·sin i

1.06 km/s

Rotation period

39.00 days

Activity index (log R'HK)

-5.040

Metallicity ratio

[M/H]

Distance

12.59 parsec

Light-years 41.05 ly

V-band magnitude

5.95 mag

Voyager-speed travel 723,888 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

79.427 mas

Total Proper Motion

539.133 mas/yr

PM Right Ascension

-485.87 mas/yr

PM Declination

-233.65 mas/yr

Galactic Cartesian (pc)

x = -0.602 · y = 0.642 · z = 0.475

Equatorial (J2000)

RA 133.14684° · Dec 28.32982°

Galactic ℓ, b

196.795° · 37.697°

Ecliptic λ, β

127.727° · 10.366°

HTM-20 index

570333148

Observation Record

Photometric series

RV measurements

Stellar spectra

Archive notes