Key parameters at a glance

A radius of 1.88 Earth radii
A mass of 7.99 Earth masses
Surface gravity around 2.27 g
An orbital period of 0.737 days
Semi-major axis 0.0154 AU
Equilibrium temperature 1,958 K (1685 °C)
Distance from Earth 41.05 light-years
Earth Similarity Index 0.129
Travel time at Voyager 1 speed 723,888 years

4 siblings around 55 Cnc

55 Cnc e 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 this	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	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 e Planet Profile

Physical Specs

Radius

1.88 R⊕

Radius (Jupiter)

0.167 R♃

Mass

7.99 M⊕

Mass (Jupiter)

0.025 M♃

Density

6.66 g/cm³

Surface Gravity

2.27 g (Earth)

Classification

Planet Type

Super-Earth

ESI Score 0.129

HZ Position Inner

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

#166of 1176

top 14.0%

This planet

1.88R⊕

Super-Earth median

1.60R⊕

Nearest-size peers

Kepler-1683 b 1.87 R⊕ TOI-2322 c 1.87 R⊕ HD 23472 c 1.87 R⊕

Metric	Earth	55 Cnc e	Jupiter
Radius (R⊕)	1.00	1.88	11.21
Mass (M⊕)	1.00	7.99	317.83
Density (g/cm³)	5.51	6.66	1.33
Surface Gravity (g)	1.00	2.27	2.53
Insolation (S⊕)	1.00	2,657.83	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	7.990 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	9.350 M⊕	Lower bound from radial-velocity fitting.
Computed mass	7.809 M⊕	Model-computed mass (e.g. from mass-radius relation).

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 Super-Earth cohort

Radius 1.875 R⊕ · percentile 86 / cohort 1176

Mass 7.990 M⊕ · percentile 95 / cohort 1176

Orbital period 0.74 d · percentile 3 / cohort 1164

Distance 12.59 pc · percentile 3 / cohort 1171

ESI 0.129 · percentile 2 / cohort 1176

Orbit & Habitability

Orbital Dynamics

Period

0.737 days

Semi-major axis

0.0154 AU

Eccentricity

0.050

Inclination

83.59 °

Year Length

A year here lasts roughly 17.7 hours long on a nearly circular orbit at a mean orbital distance of 0.0154 AU.

Transit Fingerprint

Depth

0.038 %

Duration

1.544 h

Impact parameter b

0.390

Rp / R★

0.018200

Transit midpoint (BJD)

2,457,063.2096

Photometric dip

Transit produces a flux drop of 385 ppm lasting ≈ 1.54 h.

Extended Orbital Architecture

Planet / star radius ratio

0.018200

Semi-major axis / stellar radius

3.520

Impact parameter (b)

0.390

RV semi-amplitude (K)

6.020 m/s

Occultation depth

0.008 ppm

Transit mid-time (BJD)

2,457,063.2096

Long. of periastron (ω)

86.00°

Sky-projected obliquity (λ)

72.40°

True obliquity (ψ)

23.00°

Angular separation (arcsec)

1.23000

Eq. Temperature

1,958K

(1685 °C)

Insolation (S⊕)

2,657.83

Earth = 1.00

Earth Similarity (ESI)

0.129

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched.

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

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 c · Neptune-like

Host System: 55 Cnc

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,172 K — cooler than the Sun (5,778 K)

Estimated Age

5.50 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.943 R☉

Stellar Mass

0.905 M☉

Metallicity [Fe/H]

0.35

Extended Stellar Properties

Surface gravity (log g)

4.430 dex

Stellar density

1.521 g/cm³

Systemic radial velocity

27.41 km/s

Rotational v·sin i

1.23 km/s

Rotation period

38.80 days

Activity index (log R'HK)

-5.040

Metallicity ratio

[Fe/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

Transmission spectra

Emission spectra

Archive notes