Key parameters at a glance

A radius of 5.16 Earth radii
A mass of 23.30 Earth masses
Surface gravity around 0.88 g
An orbital period of 66.500 days
Semi-major axis 0.3090 AU
Equilibrium temperature 429 K (156 °C)
Distance from Earth 973.16 light-years
Earth Similarity Index 0.417
Travel time at Voyager 1 speed 17,161,701 years

2 siblings around K2-157

K2-157 d shares its host star with 2 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
K2-157 b	Rocky Terrestrial	0.94	1.14	0.365	2,432	2018
K2-157 c	Neptune-like	6.08	30.80	25.942	587	2025
K2-157 d this	Neptune-like	5.16	23.30	66.500	429	2025

K2-157 d Planet Profile

Physical Specs

Radius

5.16 R⊕

Radius (Jupiter)

0.461 R♃

Mass

23.30 M⊕

Mass (Jupiter)

0.073 M♃

Density

0.93 g/cm³

Surface Gravity

0.88 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.417

HZ Position Inner

Controversial No

Discovery

Year 2025

Method Radial Velocity

Facility Paranal Observatory

Telescope 8.2 m ESO VLT UT3 Melipal Telescope

Size rank in cohort

Rank by radius

#362of 574

top 62.9%

This planet

5.16R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

Kepler-678 b 5.14 R⊕ TOI-3785 b 5.14 R⊕ MOA-2008-BLG-310L b 5.18 R⊕

Metric	Earth	K2-157 d	Jupiter
Radius (R⊕)	1.00	5.16	11.21
Mass (M⊕)	1.00	23.30	317.83
Density (g/cm³)	5.51	0.93	1.33
Surface Gravity (g)	1.00	0.88	2.53
Insolation (S⊕)	1.00	6.46	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	23.300 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

TIC

TIC 349445372

Gaia DR2

Gaia DR2 3596333042162818304

Gaia DR3

Gaia DR3 3596333042162818304

System

K2-157

Percentile among Neptune-like cohort

Radius 5.160 R⊕ · percentile 37 / cohort 574

Mass 23.300 M⊕ · percentile 38 / cohort 574

Orbital period 66.50 d · percentile 75 / cohort 524

Distance 298.37 pc · percentile 47 / cohort 572

ESI 0.417 · percentile 76 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

66.500 days

Semi-major axis

0.3090 AU

Eccentricity

0.500

Inclination

— °

Year Length

A year here lasts approximately 66.50 Earth days (18.2% of a terrestrial year) on a highly eccentric trajectory at a mean orbital distance of 0.3090 AU.

Extended Orbital Architecture

Semi-major axis / stellar radius

77.300

RV semi-amplitude (K)

3.960 m/s

Transit mid-time (BJD)

2,458,589.3000

Angular separation (arcsec)

1.04000

Eq. Temperature

429K

(156 °C)

Insolation (S⊕)

6.46

Earth = 1.00

Earth Similarity (ESI)

0.417

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

Discovery Paper

Primary reference

Castro Gonz & Aacute Lez et al. 2025

Instrument

ESPRESSO

Publication

2025-04

Observation locale

Ground

Discovery cohort

Planets confirmed in 2025 at Paranal Observatory (8 shown).

TOI-771 c · Super-Earth HD 35843 b · Sub-Neptune WISPIT 1 c · Gas Giant WISPIT 1 b · Gas Giant WISPIT 2 b · Gas Giant K2-157 c · Neptune-like HD 143811 AB b · Gas Giant HD 135344 A b · Gas Giant

Host System: K2-157

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,334 K — cooler than the Sun (5,778 K)

Estimated Age

8.80 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.860 R☉

Stellar Mass

0.890 M☉

Metallicity [Fe/H]

0.02

Extended Stellar Properties

Surface gravity (log g)

4.450 dex

Stellar density

1.679 g/cm³

Systemic radial velocity

43.45 km/s

Rotational v·sin i

3.00 km/s

Activity index (log R'HK)

-5.077

Metallicity ratio

[Fe/H]

Distance

298.37 parsec

Light-years 973.16 ly

V-band magnitude

12.94 mag

Voyager-speed travel 17,161,701 yr

Multi-band Host Photometry — 12 bands

Astrometric Data

Parallax

3.324 mas

Total Proper Motion

37.511 mas/yr

PM Right Ascension

36.72 mas/yr

PM Declination

-7.65 mas/yr

Galactic Cartesian (pc)

x = -0.993 · y = -0.065 · z = -0.101

Equatorial (J2000)

RA 183.75150° · Dec -5.78202°

Galactic ℓ, b

286.604° · 55.930°

Ecliptic λ, β

185.736° · -3.815°

HTM-20 index

1503740923

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