Key parameters at a glance

A radius of 2.49 Earth radii
A mass of 7.16 Earth masses
Surface gravity around 1.16 g
An orbital period of 4.990 days
Semi-major axis 0.0296 AU
Equilibrium temperature 324 K (51 °C)
Distance from Earth 86.41 light-years
Earth Similarity Index 0.713
Travel time at Voyager 1 speed 1,523,797 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

LP 791-18 (TOI-736) is a cool M dwarf star in the constellation Crater, located 26.65 parsecs away from Earth. The star is one of the smallest known stars to host exoplanets. In 2019 two exoplanets in transit around it were announced by TESS, and a third planet was discovered in Spitzer Space Telescope data in 2023.

Excerpted from Wikipedia · full article

2 siblings around LP 791-18

LP 791-18 c 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
LP 791-18 b	Rocky Terrestrial	1.21	1.94	0.948	564	2019
LP 791-18 d	Rocky Terrestrial	1.03	0.91	2.755	396	2023
LP 791-18 c this	Sub-Neptune	2.49	7.16	4.990	324	2019

LP 791-18 c Planet Profile

Physical Specs

Radius

2.49 R⊕

Radius (Jupiter)

0.222 R♃

Mass

7.16 M⊕

Mass (Jupiter)

0.023 M♃

Density

2.56 g/cm³

Surface Gravity

1.16 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.713

HZ Position Inner

Controversial No

Discovery

Year 2019

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#1208of 1978

top 61.0%

This planet

2.49R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

Kepler-1946 b 2.49 R⊕ Kepler-11 f 2.49 R⊕ Kepler-184 d 2.49 R⊕

Metric	Earth	LP 791-18 c	Jupiter
Radius (R⊕)	1.00	2.49	11.21
Mass (M⊕)	1.00	7.16	317.83
Density (g/cm³)	5.51	2.56	1.33
Surface Gravity (g)	1.00	1.16	2.53
Insolation (S⊕)	1.00	2.64	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	7.160 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 181804752

Gaia DR2

Gaia DR2 3562427951852172288

Gaia DR3

Gaia DR3 3562427951852172288

System

LP 791-18

Percentile among Sub-Neptune cohort

Radius 2.488 R⊕ · percentile 39 / cohort 1978

Mass 7.160 M⊕ · percentile 43 / cohort 1978

Orbital period 4.99 d · percentile 12 / cohort 1946

Distance 26.49 pc · percentile 6 / cohort 1975

ESI 0.713 · percentile 93 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

4.990 days

Semi-major axis

0.0296 AU

Eccentricity

0.000

Inclination

89.94 °

Year Length

A year here lasts approximately 4.99 Earth days (1.4% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0296 AU.

Transit Fingerprint

Depth

1.893 %

Duration

1.167 h

Impact parameter b

0.037

Rp / R★

0.125180

Transit midpoint (BJD)

2,458,546.5092

Photometric dip

Transit produces a flux drop of 18,931 ppm lasting ≈ 1.17 h.

Extended Orbital Architecture

Planet / star radius ratio

0.125180

Semi-major axis / stellar radius

37.050

Impact parameter (b)

0.037

Transit mid-time (BJD)

2,458,546.5092

Angular separation (arcsec)

1.12000

Eq. Temperature

324K

(51 °C)

Insolation (S⊕)

2.64

Earth = 1.00

Earth Similarity (ESI)

0.713

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — liquid water is physically possible with adequate atmospheric pressure. Close-orbiting tidally-locked around a cool host.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Crossfield et al. 2019

Instrument

TESS CCD Array

Publication

2019-09

Observation locale

Space

Discovery cohort

Planets confirmed in 2019 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

LTT 1445 A b · Super-Earth TOI-270 d · Sub-Neptune L 98-59 d · Super-Earth GJ 357 b · Rocky Terrestrial GJ 143 b · Sub-Neptune HD 23472 c · Super-Earth L 98-59 c · Super-Earth LP 791-18 b · Rocky Terrestrial TOI-270 c · Sub-Neptune HD 23472 b · Sub-Neptune TOI-270 b · Super-Earth L 98-59 b · Rocky Terrestrial

Host System: LP 791-18

Spectral Class

M-type red dwarf

Effective Temperature

2,960 K — cooler than the Sun (5,778 K)

Estimated Age

0.50 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.182 R☉

Stellar Mass

0.139 M☉

Metallicity [Fe/H]

-0.09

Extended Stellar Properties

Surface gravity (log g)

5.115 dex

Stellar density

32.511 g/cm³

Systemic radial velocity

14.10 km/s

Rotational v·sin i

2.00 km/s

Metallicity ratio

[Fe/H]

Distance

26.49 parsec

Light-years 86.41 ly

V-band magnitude

16.91 mag

Voyager-speed travel 1,523,797 yr

Multi-band Host Photometry — 15 bands

Astrometric Data

Parallax

37.718 mas

Total Proper Motion

228.815 mas/yr

PM Right Ascension

-221.08 mas/yr

PM Declination

-59.00 mas/yr

Galactic Cartesian (pc)

x = -0.930 · y = 0.237 · z = -0.282

Equatorial (J2000)

RA 165.69048° · Dec -16.40644°

Galactic ℓ, b

268.566° · 39.106°

Ecliptic λ, β

173.540° · -20.699°

HTM-20 index

2040737228

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