Key parameters at a glance

A radius of 1.13 Earth radii
A mass of 1.32 Earth masses
Surface gravity around 1.04 g
An orbital period of 12.352 days
Semi-major axis 0.0468 AU
Equilibrium temperature 197 K (-76 °C)
Distance from Earth 40.54 light-years
Earth Similarity Index 0.729
Travel time at Voyager 1 speed 714,938 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

TRAPPIST-1g is an exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1, located 40.7 light-years away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star in 2017 using observations from the Spitzer Space Telescope. The exoplanet is within the optimistic habitable zone of its host star. It was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

Excerpted from Wikipedia · full article

6 siblings around TRAPPIST-1

TRAPPIST-1 g shares its host star with 6 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
TRAPPIST-1 b	Rocky Terrestrial	1.12	1.37	1.511	398	2016
TRAPPIST-1 c	Rocky Terrestrial	1.10	1.31	2.422	340	2016
TRAPPIST-1 d	Rocky Terrestrial	0.79	0.39	4.049	286	2016
TRAPPIST-1 e	Rocky Terrestrial	0.92	0.69	6.101	250	2017
TRAPPIST-1 f	Rocky Terrestrial	1.05	1.04	9.208	218	2017
TRAPPIST-1 g this	Rocky Terrestrial	1.13	1.32	12.352	197	2017
TRAPPIST-1 h	Rocky Terrestrial	0.76	0.33	18.773	172	2017

TRAPPIST-1 g Planet Profile

Physical Specs

Radius

1.13 R⊕

Radius (Jupiter)

0.101 R♃

Mass

1.32 M⊕

Mass (Jupiter)

0.004 M♃

Density

5.06 g/cm³

Surface Gravity

1.04 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.729

HZ Position Outer

Controversial No

Discovery

Year 2017

Method Transit

Facility Multiple Observatories

Telescope Multiple Telescopes

Size rank in cohort

Rank by radius

#192of 570

top 33.5%

This planet

1.13R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-887 c 1.13 R⊕ TOI-1450 A c 1.13 R⊕ Kepler-250 b 1.13 R⊕

Metric	Earth	TRAPPIST-1 g	Jupiter
Radius (R⊕)	1.00	1.13	11.21
Mass (M⊕)	1.00	1.32	317.83
Density (g/cm³)	5.51	5.06	1.33
Surface Gravity (g)	1.00	1.04	2.53
Insolation (S⊕)	1.00	0.25	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	1.321 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 278892590

Gaia DR2

Gaia DR2 2635476908753563008

Gaia DR3

Gaia DR3 2635476908753563008

System

TRAPPIST-1

Percentile among Rocky Terrestrial cohort

Radius 1.129 R⊕ · percentile 66 / cohort 570

Mass 1.321 M⊕ · percentile 53 / cohort 570

Orbital period 12.35 d · percentile 83 / cohort 567

Distance 12.43 pc · percentile 6 / cohort 566

ESI 0.729 · percentile 84 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

12.352 days

Semi-major axis

0.0468 AU

Eccentricity

0.002

Inclination

89.74 °

Year Length

A year here lasts approximately 12.35 Earth days (3.4% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0468 AU.

Transit Fingerprint

Depth

0.756 %

Duration

1.137 h

Impact parameter b

0.379

Rp / R★

0.086920

Transit midpoint (BJD)

2,457,665.3628

Photometric dip

Transit produces a flux drop of 7,555 ppm lasting ≈ 1.14 h.

Extended Orbital Architecture

Planet / star radius ratio

0.086920

Semi-major axis / stellar radius

84.591

Impact parameter (b)

0.379

Transit mid-time (BJD)

2,457,665.3628

Long. of periastron (ω)

191.34°

Angular separation (arcsec)

3.77000

Eq. Temperature

197K

(-76 °C)

Insolation (S⊕)

0.25

Earth = 1.00

Earth Similarity (ESI)

0.729

0 = alien, 1 = Earth-identical

Beyond the outer HZ boundary (too cold) — surface water would be frozen. 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

Gillon et al. 2016

Instrument

Multiple Instruments

Publication

2016-05

Observation locale

Multiple Locales

Discovery cohort

Planets confirmed in 2017 at Multiple Observatories (12 shown).

GJ 625 b · Super-Earth TRAPPIST-1 e · Rocky Terrestrial TRAPPIST-1 f · Rocky Terrestrial TRAPPIST-1 h · Rocky Terrestrial HD 34445 e · Neptune-like BD+03 2562 b · Gas Giant HD 111591 b · Gas Giant HD 34445 d · Neptune-like MOA-2012-BLG-006L b · Gas Giant HD 76920 b · Gas Giant HD 34445 f · Neptune-like HD 40956 b · Gas Giant

Host System: TRAPPIST-1

Spectral Class

M-type red dwarf

Effective Temperature

2,566 K — cooler than the Sun (5,778 K)

Estimated Age

7.60 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.119 R☉

Stellar Mass

0.090 M☉

Metallicity [Fe/H]

0.05

Extended Stellar Properties

Surface gravity (log g)

5.240 dex

Stellar density

75.050 g/cm³

Rotational v·sin i

2.04 km/s

Rotation period

1.40 days

Metallicity ratio

[Fe/H]

Distance

12.43 parsec

Light-years 40.54 ly

V-band magnitude

17.02 mag

Voyager-speed travel 714,938 yr

Multi-band Host Photometry — 13 bands

Astrometric Data

Parallax

80.451 mas

Total Proper Motion

1,026.579 mas/yr

PM Right Ascension

901.00 mas/yr

PM Declination

-492.00 mas/yr

Galactic Cartesian (pc)

x = 0.969 · y = -0.230 · z = -0.088

Equatorial (J2000)

RA 346.62639° · Dec -5.04346°

Galactic ℓ, b

69.715° · -56.649°

Ecliptic λ, β

345.733° · 0.630°

HTM-20 index

915425164

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