Key parameters at a glance

A radius of 1.03 Earth radii
A mass of 0.91 Earth masses
Surface gravity around 0.85 g
An orbital period of 2.755 days
Semi-major axis 0.0199 AU
Equilibrium temperature 396 K (122 °C)
Distance from Earth 86.41 light-years
Earth Similarity Index 0.761
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 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
LP 791-18 b	Rocky Terrestrial	1.21	1.94	0.948	564	2019
LP 791-18 d this	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 d Planet Profile

Physical Specs

Radius

1.03 R⊕

Radius (Jupiter)

0.092 R♃

Mass

0.91 M⊕

Mass (Jupiter)

0.003 M♃

Density

4.56 g/cm³

Surface Gravity

0.85 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.761

HZ Position Inner

Controversial No

Discovery

Year 2023

Method Transit

Facility Spitzer Space Telescope

Telescope 0.85 m Spitzer Space Telescope

Size rank in cohort

Rank by radius

#296of 570

top 51.8%

This planet

1.03R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-1948 b 1.03 R⊕ Kepler-387 b 1.03 R⊕ Kepler-1398 c 1.03 R⊕

Metric	Earth	LP 791-18 d	Jupiter
Radius (R⊕)	1.00	1.03	11.21
Mass (M⊕)	1.00	0.91	317.83
Density (g/cm³)	5.51	4.56	1.33
Surface Gravity (g)	1.00	0.85	2.53
Insolation (S⊕)	1.00	5.83	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.910 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 Rocky Terrestrial cohort

Radius 1.032 R⊕ · percentile 48 / cohort 570

Mass 0.910 M⊕ · percentile 34 / cohort 570

Orbital period 2.75 d · percentile 31 / cohort 567

Distance 26.49 pc · percentile 12 / cohort 566

ESI 0.761 · percentile 85 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

2.755 days

Semi-major axis

0.0199 AU

Eccentricity

0.001

Inclination

89.34 °

Year Length

A year here lasts approximately 2.75 Earth days (0.8% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0199 AU.

Transit Fingerprint

Duration

0.915 h

Impact parameter b

0.270

Rp / R★

0.051920

Transit midpoint (BJD)

2,458,546.3789

Extended Orbital Architecture

Planet / star radius ratio

0.051920

Impact parameter (b)

0.270

Transit mid-time (BJD)

2,458,546.3789

Angular separation (arcsec)

0.75200

Eq. Temperature

396K

(122 °C)

Insolation (S⊕)

5.83

Earth = 1.00

Earth Similarity (ESI)

0.761

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.

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

Peterson et al. 2023

Instrument

IRAC Infrared Array Camera

Publication

2023-05

Observation locale

Space

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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