Key parameters at a glance

A radius of 0.98 Earth radii
A mass of 0.89 Earth masses
Surface gravity around 0.94 g
An orbital period of 0.719 days
Semi-major axis 0.0073 AU
Equilibrium temperature 553 K (280 °C)
Earth Similarity Index 0.583
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

SPECULOOS-3 b is an Earth-sized exoplanet, orbiting the ultracool red dwarf star SPECULOOS-3. It is relatively close to Earth, at a distance of 55 light-years. SPECULOOS-3 b takes only about 17 hours to complete an orbit around SPECULOOS-3, and, because of that proximity, it receives very high levels of radiation and is tidally locked, meaning that one side of the planet always faces its host star. Its discovery was made using the SPECULOOS project, and announced in May 2024 in the academic journal Nature Astronomy.

Excerpted from Wikipedia · full article

SPECULOOS-3 b Planet Profile

Physical Specs

Radius

0.98 R⊕

Radius (Jupiter)

0.087 R♃

Mass

0.89 M⊕

Mass (Jupiter)

0.003 M♃

Density

5.27 g/cm³

Surface Gravity

0.94 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.583

HZ Position Inner

Controversial No

Discovery

Year 2024

Method Transit

Facility SPECULOOS Southern Observatory

Telescope Multiple Telescopes

Size rank in cohort

Rank by radius

#360of 570

top 63.0%

This planet

0.98R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-1693 c 0.98 R⊕ Kepler-68 c 0.98 R⊕ Kepler-220 d 0.98 R⊕

Metric	Earth	SPECULOOS-3 b	Jupiter
Radius (R⊕)	1.00	0.98	11.21
Mass (M⊕)	1.00	0.89	317.83
Density (g/cm³)	5.51	5.27	1.33
Surface Gravity (g)	1.00	0.94	2.53
Insolation (S⊕)	1.00	15.54	0.037

Star Catalogue Identifiers

TIC

TIC 230741378

Gaia DR2

Gaia DR2 1869054868256849920

Gaia DR3

Gaia DR3 1869054868256849920

System

SPECULOOS-3

Percentile among Rocky Terrestrial cohort

Radius 0.977 R⊕ · percentile 37 / cohort 570

Mass 0.894 M⊕ · percentile 32 / cohort 570

Orbital period 0.72 d · percentile 6 / cohort 567

ESI 0.583 · percentile 76 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

0.719 days

Semi-major axis

0.0073 AU

Eccentricity

—

Inclination

89.44 °

Year Length

A year here lasts roughly 17.3 hours long at a mean orbital distance of 0.0073 AU.

Transit Fingerprint

Depth

0.529 %

Duration

0.456 h

Impact parameter b

0.124

Rp / R★

0.072730

Transit midpoint (BJD)

2,459,790.5834

Photometric dip

Transit produces a flux drop of 5,291 ppm lasting ≈ 0.46 h.

Extended Orbital Architecture

Planet / star radius ratio

0.072730

Semi-major axis / stellar radius

12.810

Impact parameter (b)

0.124

Transit mid-time (BJD)

2,459,790.5834

Eq. Temperature

553K

(280 °C)

Insolation (S⊕)

15.54

Earth = 1.00

Earth Similarity (ESI)

0.583

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

Gillon et al. 2024

Instrument

Multiple Instruments

Publication

2024-05

Observation locale

Ground

Host System: SPECULOOS-3

Spectral Class

M-type red dwarf

Effective Temperature

2,800 K — cooler than the Sun (5,778 K)

Estimated Age

6.60 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.123 R☉

Stellar Mass

0.101 M☉

Metallicity [Fe/H]

0.07

Extended Stellar Properties

Surface gravity (log g)

5.265 dex

Stellar density

77.118 g/cm³

Systemic radial velocity

17.82 km/s

Rotational v·sin i

4.20 km/s

Metallicity ratio

[Fe/H]

Multi-band Host Photometry — 6 bands

Astrometric Data

Total Proper Motion

459.296 mas/yr

PM Right Ascension

-203.00 mas/yr

PM Declination

-412.00 mas/yr

Galactic Cartesian (pc)

x = 0.561 · y = -0.615 · z = 0.554

Equatorial (J2000)

RA 312.36326° · Dec 33.61238°

Galactic ℓ, b

76.092° · -6.465°

Ecliptic λ, β

328.460° · 48.822°

HTM-20 index

-1157377204

Wikipedia → Image: Wikimedia Commons · NASA/JPL-Caltech · Public domain