Key parameters at a glance

A radius of 1.10 Earth radii
A mass of 1.31 Earth masses
Surface gravity around 1.09 g
An orbital period of 2.422 days
Semi-major axis 0.0158 AU
Equilibrium temperature 340 K (67 °C)
Distance from Earth 40.54 light-years
Earth Similarity Index 0.873
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-1c is a mainly rocky exoplanet orbiting around the ultracool dwarf star TRAPPIST-1, located 40.7 light-years (12.5 parsecs) away from Earth in the constellation Aquarius. It is the third most massive and third largest planet of the system, with about 131% the mass and 110% the radius of Earth. Its density indicates a primarily rocky composition, and observations by the James Webb Space Telescope announced in 2023 suggests against a thick CO2 atmosphere, however this does not exclude a thick abiotic oxygen-dominated atmosphere as is hypothesized to be common around red dwarf stars.

Excerpted from Wikipedia · full article

6 siblings around TRAPPIST-1

TRAPPIST-1 c 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 this	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	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 c Planet Profile

Physical Specs

Radius

1.10 R⊕

Radius (Jupiter)

0.098 R♃

Mass

1.31 M⊕

Mass (Jupiter)

0.004 M♃

Density

5.46 g/cm³

Surface Gravity

1.09 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.873

HZ Position Inner

Controversial No

Discovery

Year 2016

Method Transit

Facility La Silla Observatory

Telescope 0.60 m Transiting Planets and Planetesimals Small Telescope

Size rank in cohort

Rank by radius

#237of 570

top 41.4%

This planet

1.10R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

K2-239 d 1.10 R⊕ Kepler-392 c 1.10 R⊕ Kepler-59 b 1.10 R⊕

Metric	Earth	TRAPPIST-1 c	Jupiter
Radius (R⊕)	1.00	1.10	11.21
Mass (M⊕)	1.00	1.31	317.83
Density (g/cm³)	5.51	5.46	1.33
Surface Gravity (g)	1.00	1.09	2.53
Insolation (S⊕)	1.00	2.21	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	1.308 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 1.097 R⊕ · percentile 58 / cohort 570

Mass 1.308 M⊕ · percentile 51 / cohort 570

Orbital period 2.42 d · percentile 28 / cohort 567

Distance 12.43 pc · percentile 6 / cohort 566

ESI 0.873 · percentile 90 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

2.422 days

Semi-major axis

0.0158 AU

Eccentricity

0.007

Inclination

89.78 °

Year Length

A year here lasts approximately 2.42 Earth days (0.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0158 AU.

Transit Fingerprint

Depth

0.712 %

Duration

0.701 h

Impact parameter b

0.109

Rp / R★

0.084400

Transit midpoint (BJD)

2,457,282.8114

Photometric dip

Transit produces a flux drop of 7,123 ppm lasting ≈ 0.70 h.

Extended Orbital Architecture

Planet / star radius ratio

0.084400

Semi-major axis / stellar radius

28.549

Impact parameter (b)

0.109

Transit mid-time (BJD)

2,457,282.8114

Long. of periastron (ω)

282.45°

Angular separation (arcsec)

1.27000

Eq. Temperature

340K

(67 °C)

Insolation (S⊕)

2.21

Earth = 1.00

Earth Similarity (ESI)

0.873

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

Gillon et al. 2016

Instrument

TRAPPISTCAM

Publication

2016-05

Observation locale

Ground

Discovery cohort

Planets confirmed in 2016 at La Silla Observatory (5 shown).

TRAPPIST-1 d · Rocky Terrestrial TRAPPIST-1 b · Rocky Terrestrial GJ 536 b · Sub-Neptune HD 111998 b · Gas Giant NGC 2682 YBP 401 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

Observation Record

Transmission spectra

Emission spectra

Archive notes

Wikipedia → Image: Wikimedia Commons · NASA, ESA, CSA, Joseph Olmsted (STScI) · Public domain