Key parameters at a glance

A radius of 4.17 Earth radii
A mass of 22.10 Earth masses
Surface gravity around 1.27 g
An orbital period of 2.644 days
Semi-major axis 0.0291 AU
Equilibrium temperature 686 K (413 °C)
Distance from Earth 31.81 light-years
Earth Similarity Index 0.318
Travel time at Voyager 1 speed 560,981 years
Almost certainly tidally locked to its host star given the close orbit

GJ 436 b Planet Profile

Physical Specs

Radius

4.17 R⊕

Radius (Jupiter)

0.372 R♃

Mass

22.10 M⊕

Mass (Jupiter)

0.070 M♃

Density

1.80 g/cm³

Surface Gravity

1.27 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.318

HZ Position Inner

Controversial No

Discovery

Year 2004

Method Radial Velocity

Facility W. M. Keck Observatory

Telescope 10 m Keck I Telescope

Size rank in cohort

Rank by radius

#526of 574

top 91.5%

This planet

4.17R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

GJ 2056 b 4.17 R⊕ Kepler-619 d 4.17 R⊕ Kepler-421 b 4.16 R⊕

Metric	Earth	GJ 436 b	Jupiter
Radius (R⊕)	1.00	4.17	11.21
Mass (M⊕)	1.00	22.10	317.83
Density (g/cm³)	5.51	1.80	1.33
Surface Gravity (g)	1.00	1.27	2.53
Insolation (S⊕)	1.00	29.43	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	22.100 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	21.360 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HIP

HIP 57087

TIC

TIC 138819293

Gaia DR2

Gaia DR2 4017860992519744384

Gaia DR3

Gaia DR3 4017860992519744384

System

GJ 436

Percentile among Neptune-like cohort

Radius 4.170 R⊕ · percentile 8 / cohort 574

Mass 22.100 M⊕ · percentile 35 / cohort 574

Orbital period 2.64 d · percentile 2 / cohort 524

Distance 9.75 pc · percentile 2 / cohort 572

ESI 0.318 · percentile 54 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

2.644 days

Semi-major axis

0.0291 AU

Eccentricity

0.138

Inclination

86.44 °

Year Length

A year here lasts approximately 2.64 Earth days (0.7% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0291 AU.

Transit Fingerprint

Depth

0.682 %

Duration

1.005 h

Impact parameter b

0.736

Rp / R★

0.082200

Transit midpoint (BJD)

2,454,510.8016

Photometric dip

Transit produces a flux drop of 6,819 ppm lasting ≈ 1.01 h.

Extended Orbital Architecture

Planet / star radius ratio

0.082200

Semi-major axis / stellar radius

13.730

Impact parameter (b)

0.736

RV semi-amplitude (K)

17.090 m/s

Transit mid-time (BJD)

2,454,510.8016

Long. of periastron (ω)

351.00°

Sky-projected obliquity (λ)

72.00°

True obliquity (ψ)

80.00°

Angular separation (arcsec)

2.98000

Eq. Temperature

686K

(413 °C)

Insolation (S⊕)

29.43

Earth = 1.00

Earth Similarity (ESI)

0.318

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

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

Butler et al. 2004

Instrument

HIRES Spectrometer

Publication

2004-12

Observation locale

Ground

Discovery cohort

Planets confirmed in 2004 at W. M. Keck Observatory (6 shown).

HD 99492 b · Neptune-like HD 183263 b · Gas Giant HD 117207 b · Gas Giant HD 45350 b · Gas Giant HD 188015 b · Gas Giant HD 88133 b · Gas Giant

Host System: GJ 436

Spectral Class

M-type red dwarf

Effective Temperature

3,586 K — cooler than the Sun (5,778 K)

Estimated Age

6.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.455 R☉

Stellar Mass

0.470 M☉

Metallicity [Fe/H]

0.10

Extended Stellar Properties

Surface gravity (log g)

4.792 dex

Stellar density

7.000 g/cm³

Systemic radial velocity

9.60 km/s

Rotational v·sin i

0.33 km/s

Rotation period

44.09 days

Metallicity ratio

[Fe/H]

Distance

9.75 parsec

Light-years 31.81 ly

V-band magnitude

10.67 mag

Voyager-speed travel 560,981 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

102.501 mas

Total Proper Motion

1,209.858 mas/yr

PM Right Ascension

895.05 mas/yr

PM Declination

-814.03 mas/yr

Galactic Cartesian (pc)

x = -0.891 · y = 0.069 · z = 0.449

Equatorial (J2000)

RA 175.55054° · Dec 26.70307°

Galactic ℓ, b

210.556° · 74.572°

Ecliptic λ, β

164.775° · 22.626°

HTM-20 index

-55855595

Observation Record

Photometric series

RV measurements

Stellar spectra

Transmission spectra

Emission spectra