Key parameters at a glance

A radius of 12.78 Earth radii
A mass of 680.15 Earth masses
Surface gravity around 4.17 g
An orbital period of 6.135 days
Semi-major axis 0.0713 AU
Equilibrium temperature 1,361 K (1088 °C)
Distance from Earth 300.91 light-years
Earth Similarity Index 0.113
Travel time at Voyager 1 speed 5,306,511 years
Almost certainly tidally locked to its host star given the close orbit

1 sibling around HD 118203

HD 118203 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 118203 b this	Gas Giant	12.78	680.15	6.135	1,361	2005
HD 118203 c	Gas Giant	12.40	3,747.20	5,103.000	146	2024

HD 118203 b Planet Profile

Physical Specs

Radius

12.78 R⊕

Radius (Jupiter)

1.140 R♃

Mass

680.15 M⊕

Mass (Jupiter)

2.140 M♃

Density

1.79 g/cm³

Surface Gravity

4.17 g (Earth)

Classification

Planet Type

Gas Giant

ESI Score 0.113

HZ Position Inner

Controversial No

Discovery

Year 2005

Method Radial Velocity

Facility Haute-Provence Observatory

Telescope 1.93 m Telescope

Size rank in cohort

Rank by radius

#1120of 1771

top 63.2%

This planet

12.78R⊕

Gas Giant median

13.52R⊕

Nearest-size peers

TOI-1820 b 12.78 R⊕ TOI-5232 b 12.78 R⊕ WASP-97 b 12.78 R⊕

Metric	Earth	HD 118203 b	Jupiter
Radius (R⊕)	1.00	12.78	11.21
Mass (M⊕)	1.00	680.15	317.83
Density (g/cm³)	5.51	1.79	1.33
Surface Gravity (g)	1.00	4.17	2.53
Insolation (S⊕)	1.00	593.40	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	680.153 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	688.099 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 118203

HIP

HIP 66192

TIC

TIC 286923464

Gaia DR2

Gaia DR2 1560420854826284928

Gaia DR3

Gaia DR3 1560420854826284928

System

HD 118203

Percentile among Gas Giant cohort

Radius 12.778 R⊕ · percentile 37 / cohort 1771

Mass 680.153 M⊕ · percentile 57 / cohort 1747

Orbital period 6.13 d · percentile 40 / cohort 1533

Distance 92.26 pc · percentile 33 / cohort 1759

ESI 0.113 · percentile 30 / cohort 1771

Orbit & Habitability

Orbital Dynamics

Period

6.135 days

Semi-major axis

0.0713 AU

Eccentricity

0.314

Inclination

88.48 °

Year Length

A year here lasts approximately 6.13 Earth days (1.7% of a terrestrial year) on a highly eccentric trajectory at a mean orbital distance of 0.0713 AU.

Transit Fingerprint

Depth

0.386 %

Duration

5.643 h

Impact parameter b

0.155

Rp / R★

0.055730

Transit midpoint (BJD)

2,458,731.0642

Photometric dip

Transit produces a flux drop of 3,860 ppm lasting ≈ 5.64 h.

Extended Orbital Architecture

Planet / star radius ratio

0.055730

Semi-major axis / stellar radius

7.460

Impact parameter (b)

0.155

RV semi-amplitude (K)

216.900 m/s

Transit mid-time (BJD)

2,458,731.0642

Long. of periastron (ω)

155.50°

Sky-projected obliquity (λ)

-11.70°

True obliquity (ψ)

75.00°

Angular separation (arcsec)

0.77300

Eq. Temperature

1,361K

(1088 °C)

Insolation (S⊕)

593.40

Earth = 1.00

Earth Similarity (ESI)

0.113

0 = alien, 1 = Earth-identical

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

Da Silva et al. 2006

Instrument

ELODIE Spectrograph

Publication

2006-02

Observation locale

Ground

Discovery cohort

Planets confirmed in 2005 at Haute-Provence Observatory (3 shown).

HD 33564 b · Gas Giant HD 149143 b · Gas Giant HD 189733 b · Gas Giant

Host System: HD 118203

Spectral Class

K-type orange

Effective Temperature

5,742 K — cooler than the Sun (5,778 K)

Estimated Age

4.73 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

2.040 R☉

Stellar Mass

1.270 M☉

Metallicity [Fe/H]

0.29

Extended Stellar Properties

Surface gravity (log g)

3.920 dex

Stellar density

0.196 g/cm³

Systemic radial velocity

-29.36 km/s

Rotational v·sin i

5.89 km/s

Rotation period

23.10 days

Metallicity ratio

[Fe/H]

Distance

92.26 parsec

Light-years 300.91 ly

V-band magnitude

8.05 mag

Voyager-speed travel 5,306,511 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

10.810 mas

Total Proper Motion

116.628 mas/yr

PM Right Ascension

-85.88 mas/yr

PM Declination

-78.91 mas/yr

Galactic Cartesian (pc)

x = -0.543 · y = -0.236 · z = 0.806

Equatorial (J2000)

RA 203.50996° · Dec 53.72819°

Galactic ℓ, b

109.345° · 62.262°

Ecliptic λ, β

169.127° · 56.467°

HTM-20 index

814331595

Observation Record

Photometric series

RV measurements

Archive notes

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Explore Related Categories

Gas Giant Planets Radial Velocity Discoveries Haute-Provence Observatory Mission K-type orange Hosts