Key parameters at a glance

A radius of 14.20 Earth radii
A mass of 166.22 Earth masses
Surface gravity around 0.82 g
An orbital period of 3.097 days
Semi-major axis 0.0426 AU
Distance from Earth 149.88 light-years
Earth Similarity Index 0.257
Travel time at Voyager 1 speed 2,643,210 years

1 sibling around HD 187123

HD 187123 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 187123 b this	Gas Giant	14.20	166.22	3.097	—	1998
HD 187123 c	Gas Giant	13.20	912.17	3,810.000	—	2008

HD 187123 b Planet Profile

Physical Specs

Radius

14.20 R⊕

Radius (Jupiter)

1.270 R♃

Mass

166.22 M⊕

Mass (Jupiter)

0.523 M♃

Density

0.32 g/cm³

Surface Gravity

0.82 g (Earth)

Classification

Planet Type

Gas Giant

ESI Score 0.257

HZ Position Unknown

Controversial No

Discovery

Year 1998

Method Radial Velocity

Facility W. M. Keck Observatory

Telescope 10 m Keck I Telescope

Size rank in cohort

Rank by radius

#334of 1771

top 18.8%

This planet

14.20R⊕

Gas Giant median

13.52R⊕

Nearest-size peers

OGLE-2011-BLG-0251L b 14.20 R⊕ OGLE-2017-BLG-0406L b 14.20 R⊕ HIP 57274 c 14.20 R⊕

Metric	Earth	HD 187123 b	Jupiter
Radius (R⊕)	1.00	14.20	11.21
Mass (M⊕)	1.00	166.22	317.83
Density (g/cm³)	5.51	0.32	1.33
Surface Gravity (g)	1.00	0.82	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	166.218 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 187123

HIP

HIP 97336

TIC

TIC 58559140

Gaia DR2

Gaia DR2 2047452661412980736

Gaia DR3

Gaia DR3 2047452661412980736

System

HD 187123

Percentile among Gas Giant cohort

Radius 14.200 R⊕ · percentile 79 / cohort 1771

Mass 166.218 M⊕ · percentile 14 / cohort 1747

Orbital period 3.10 d · percentile 17 / cohort 1533

Distance 45.95 pc · percentile 17 / cohort 1759

ESI 0.257 · percentile 47 / cohort 1771

Orbit & Habitability

Orbital Dynamics

Period

3.097 days

Semi-major axis

0.0426 AU

Eccentricity

0.010

Inclination

79.00 °

Year Length

A year here lasts approximately 3.10 Earth days (0.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0426 AU.

Extended Orbital Architecture

RV semi-amplitude (K)

69.400 m/s

Transit mid-time (BJD)

2,455,665.9340

Long. of periastron (ω)

25.00°

Angular separation (arcsec)

0.92700

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.257

0 = alien, 1 = Earth-identical

Detection Signatures

Radial velocity

Stellar wobble has been measured spectroscopically.

Astrometry

Positional wobble of the host star was measured.

Discovery Paper

Primary reference

Butler et al. 1998

Instrument

HIRES Spectrometer

Publication

1998-12

Observation locale

Ground

Discovery cohort

Planets confirmed in 1998 at W. M. Keck Observatory (2 shown).

HD 168443 b · Gas Giant HD 210277 b · Gas Giant

Host System: HD 187123

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,790 K — hotter than the Sun (5,778 K)

Estimated Age

7.40 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

1.150 R☉

Stellar Mass

1.040 M☉

Metallicity [Fe/H]

0.09

Extended Stellar Properties

Surface gravity (log g)

4.333 dex

Stellar density

0.963 g/cm³

Systemic radial velocity

-16.99 km/s

Rotational v·sin i

2.10 km/s

Activity index (log R'HK)

-5.030

Metallicity ratio

[M/H]

Distance

45.95 parsec

Light-years 149.88 ly

V-band magnitude

7.83 mag

Voyager-speed travel 2,643,210 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

21.732 mas

Total Proper Motion

188.698 mas/yr

PM Right Ascension

142.58 mas/yr

PM Declination

-123.60 mas/yr

Galactic Cartesian (pc)

x = 0.371 · y = -0.737 · z = 0.565

Equatorial (J2000)

RA 296.74288° · Dec 34.41899°

Galactic ℓ, b

69.466° · 4.679°

Ecliptic λ, β

309.449° · 54.256°

HTM-20 index

-767094899

Observation Record

Photometric series

RV measurements

Stellar spectra