Key parameters at a glance

A radius of 12.22 Earth radii
A mass of 387.75 Earth masses
Surface gravity around 2.60 g
An orbital period of 3.634 days
Semi-major axis 0.0494 AU
Equilibrium temperature 1,590 K (1317 °C)
Distance from Earth 1,351.05 light-years
Earth Similarity Index 0.090
Travel time at Voyager 1 speed 23,825,749 years

WASP-138 b Planet Profile

Physical Specs

Radius

12.22 R⊕

Radius (Jupiter)

1.090 R♃

Mass

387.75 M⊕

Mass (Jupiter)

1.220 M♃

Density

1.20 g/cm³

Surface Gravity

2.60 g (Earth)

Classification

Planet Type

Gas Giant

ESI Score 0.090

HZ Position Inner

Controversial No

Discovery

Year 2016

Method Transit

Facility SuperWASP

Telescope Canon 200mm f/1.8L

Size rank in cohort

Rank by radius

#1404of 1771

top 79.2%

This planet

12.22R⊕

Gas Giant median

13.52R⊕

Nearest-size peers

HAT-P-31 b 12.22 R⊕ WASP-160 B b 12.22 R⊕ NGTS-8 b 12.22 R⊕

Metric	Earth	WASP-138 b	Jupiter
Radius (R⊕)	1.00	12.22	11.21
Mass (M⊕)	1.00	387.75	317.83
Density (g/cm³)	5.51	1.20	1.33
Surface Gravity (g)	1.00	2.60	2.53
Insolation (S⊕)	1.00	1,133.73	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	387.753 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 35857242

Gaia DR2

Gaia DR2 2498515516990171392

Gaia DR3

Gaia DR3 2498515516990171392

System

WASP-138

Percentile among Gas Giant cohort

Radius 12.218 R⊕ · percentile 21 / cohort 1771

Mass 387.753 M⊕ · percentile 41 / cohort 1747

Orbital period 3.63 d · percentile 25 / cohort 1533

Distance 414.23 pc · percentile 71 / cohort 1759

ESI 0.090 · percentile 23 / cohort 1771

Orbit & Habitability

Orbital Dynamics

Period

3.634 days

Semi-major axis

0.0494 AU

Eccentricity

—

Inclination

88.50 °

Year Length

A year here lasts approximately 3.63 Earth days (1.0% of a terrestrial year) at a mean orbital distance of 0.0494 AU.

Transit Fingerprint

Depth

0.683 %

Duration

3.773 h

Impact parameter b

0.190

Rp / R★

0.082600

Transit midpoint (BJD)

2,457,326.6218

Photometric dip

Transit produces a flux drop of 6,830 ppm lasting ≈ 3.77 h.

Extended Orbital Architecture

Planet / star radius ratio

0.082600

Semi-major axis / stellar radius

7.390

Impact parameter (b)

0.190

Transit mid-time (BJD)

2,457,326.6218

Angular separation (arcsec)

0.11900

Eq. Temperature

1,590K

(1317 °C)

Insolation (S⊕)

1,133.73

Earth = 1.00

Earth Similarity (ESI)

0.090

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

Lam et al. 2017

Instrument

iKon-L CCD Camera

Publication

2017-03

Observation locale

Ground

Discovery cohort

Planets confirmed in 2016 at SuperWASP (11 shown).

WASP-157 b · Gas Giant WASP-120 b · Gas Giant WASP-123 b · Gas Giant WASP-136 b · Gas Giant WASP-127 b · Gas Giant WASP-118 b · Gas Giant WASP-92 b · Gas Giant WASP-93 b · Gas Giant WASP-90 b · Gas Giant WASP-121 b · Gas Giant WASP-76 b · Gas Giant

Host System: WASP-138

Spectral Class

F-type yellow-white

Effective Temperature

6,272 K — hotter than the Sun (5,778 K)

Estimated Age

3.44 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

1.360 R☉

Stellar Mass

1.220 M☉

Metallicity [Fe/H]

-0.09

Extended Stellar Properties

Surface gravity (log g)

4.250 dex

Stellar density

0.687 g/cm³

Rotational v·sin i

7.70 km/s

Metallicity ratio

[Fe/H]

Distance

414.23 parsec

Light-years 1,351.05 ly

V-band magnitude

11.80 mag

Voyager-speed travel 23,825,749 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

2.386 mas

Total Proper Motion

36.252 mas/yr

PM Right Ascension

11.25 mas/yr

PM Declination

-34.46 mas/yr

Galactic Cartesian (pc)

x = 0.747 · y = 0.664 · z = -0.008

Equatorial (J2000)

RA 41.63916° · Dec -0.46413°

Galactic ℓ, b

173.747° · -51.603°

Ecliptic λ, β

39.052° · -15.767°

HTM-20 index

1655872869