Key parameters at a glance

A radius of 1.21 Earth radii
A mass of 1.94 Earth masses
Surface gravity around 1.32 g
An orbital period of 0.948 days
Semi-major axis 0.0098 AU
Equilibrium temperature 564 K (291 °C)
Distance from Earth 86.41 light-years
Earth Similarity Index 0.552
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 b 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 this	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	Sub-Neptune	2.49	7.16	4.990	324	2019

LP 791-18 b Planet Profile

Physical Specs

Radius

1.21 R⊕

Radius (Jupiter)

0.108 R♃

Mass

1.94 M⊕

Mass (Jupiter)

0.006 M♃

Density

5.99 g/cm³

Surface Gravity

1.32 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.552

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

#54of 570

top 9.3%

This planet

1.21R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

K2-32 e 1.21 R⊕ Kepler-415 b 1.21 R⊕ Kepler-169 c 1.21 R⊕

Metric	Earth	LP 791-18 b	Jupiter
Radius (R⊕)	1.00	1.21	11.21
Mass (M⊕)	1.00	1.94	317.83
Density (g/cm³)	5.51	5.99	1.33
Surface Gravity (g)	1.00	1.32	2.53
Insolation (S⊕)	1.00	24.14	0.037

Star Catalogue Identifiers

TIC

TIC 181804752

Gaia DR2

Gaia DR2 3562427951852172288

Gaia DR3

Gaia DR3 3562427951852172288

System

LP 791-18

Percentile among Rocky Terrestrial cohort

Radius 1.212 R⊕ · percentile 90 / cohort 570

Mass 1.940 M⊕ · percentile 82 / cohort 570

Orbital period 0.95 d · percentile 10 / cohort 567

Distance 26.49 pc · percentile 12 / cohort 566

ESI 0.552 · percentile 74 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

0.948 days

Semi-major axis

0.0098 AU

Eccentricity

0.000

Inclination

88.37 °

Year Length

A year here lasts roughly 22.8 hours long on a nearly circular orbit at a mean orbital distance of 0.0098 AU.

Transit Fingerprint

Depth

0.420 %

Duration

0.620 h

Impact parameter b

0.330

Rp / R★

0.061000

Transit midpoint (BJD)

2,458,774.8697

Photometric dip

Transit produces a flux drop of 4,201 ppm lasting ≈ 0.62 h.

Extended Orbital Architecture

Planet / star radius ratio

0.061000

Semi-major axis / stellar radius

11.000

Impact parameter (b)

0.330

Transit mid-time (BJD)

2,458,774.8697

Angular separation (arcsec)

0.36900

Eq. Temperature

564K

(291 °C)

Insolation (S⊕)

24.14

Earth = 1.00

Earth Similarity (ESI)

0.552

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water. Close-orbiting tidally-locked around a cool host.

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).

LP 791-18 c · Sub-Neptune 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 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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