Key parameters at a glance

A radius of 1.20 Earth radii
A mass of 0.96 Earth masses
Surface gravity around 0.67 g
An orbital period of 1.915 days
Semi-major axis 0.0261 AU
Equilibrium temperature 1,040 K (767 °C)
Distance from Earth 204.50 light-years
Earth Similarity Index 0.280
Travel time at Voyager 1 speed 3,606,296 years
Almost certainly tidally locked to its host star given the close orbit

5 siblings around TOI-178

TOI-178 b shares its host star with 5 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
TOI-178 b this	Rocky Terrestrial	1.20	0.96	1.915	1,040	2021
TOI-178 c	Super-Earth	1.75	4.64	3.238	873	2021
TOI-178 d	Sub-Neptune	2.70	5.20	6.558	690	2021
TOI-178 e	Sub-Neptune	2.30	3.48	9.963	600	2021
TOI-178 f	Sub-Neptune	2.42	5.63	15.233	521	2021
TOI-178 g	Sub-Neptune	2.94	4.40	20.717	470	2021

TOI-178 b Planet Profile

Physical Specs

Radius

1.20 R⊕

Radius (Jupiter)

0.107 R♃

Mass

0.96 M⊕

Mass (Jupiter)

0.003 M♃

Density

3.14 g/cm³

Surface Gravity

0.67 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.280

HZ Position Unknown

Controversial No

Discovery

Year 2021

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#75of 570

top 13.0%

This planet

1.20R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-225 b 1.20 R⊕ Kepler-282 c 1.20 R⊕ Kepler-367 c 1.20 R⊕

Metric	Earth	TOI-178 b	Jupiter
Radius (R⊕)	1.00	1.20	11.21
Mass (M⊕)	1.00	0.96	317.83
Density (g/cm³)	5.51	3.14	1.33
Surface Gravity (g)	1.00	0.67	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.960 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 251848941

Gaia DR2

Gaia DR2 2318295979126499200

Gaia DR3

Gaia DR3 2318295979126499200

System

TOI-178

Percentile among Rocky Terrestrial cohort

Radius 1.200 R⊕ · percentile 84 / cohort 570

Mass 0.960 M⊕ · percentile 35 / cohort 570

Orbital period 1.91 d · percentile 21 / cohort 567

Distance 62.70 pc · percentile 19 / cohort 566

ESI 0.280 · percentile 32 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

1.915 days

Semi-major axis

0.0261 AU

Eccentricity

—

Inclination

88.80 °

Year Length

A year here lasts approximately 1.91 Earth days (0.5% of a terrestrial year) at a mean orbital distance of 0.0261 AU.

Transit Fingerprint

Depth

0.028 %

Duration

1.692 h

Impact parameter b

0.336

Rp / R★

0.016630

Transit midpoint (BJD)

2,458,931.1793

Photometric dip

Transit produces a flux drop of 277 ppm lasting ≈ 1.69 h.

Extended Orbital Architecture

Planet / star radius ratio

0.016630

Semi-major axis / stellar radius

8.610

Impact parameter (b)

0.336

RV semi-amplitude (K)

1.050 m/s

Transit mid-time (BJD)

2,458,931.1793

Angular separation (arcsec)

0.41600

Eq. Temperature

1,040K

(767 °C)

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.280

0 = alien, 1 = Earth-identical

Insufficient insolation data — the dayside is scorched. Close-orbiting tidally-locked around a cool host.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Radial velocity

Stellar wobble has been measured spectroscopically.

Discovery Paper

Primary reference

Leleu et al. 2021

Instrument

TESS CCD Array

Publication

2021-05

Observation locale

Space

Discovery cohort

Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

TOI-2257 b · Sub-Neptune TOI-2285 b · Super-Earth TOI-1231 b · Sub-Neptune AU Mic c · Sub-Neptune LHS 1678 c · Rocky Terrestrial LHS 1478 b · Rocky Terrestrial TOI-2406 b · Sub-Neptune HD 207897 b · Sub-Neptune TOI-269 b · Sub-Neptune TIC 172900988 b · Gas Giant TOI-178 g · Sub-Neptune TOI-2076 d · Sub-Neptune

Host System: TOI-178

Spectral Class

K-type orange

Effective Temperature

4,316 K — cooler than the Sun (5,778 K)

Estimated Age

6.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.662 R☉

Stellar Mass

0.647 M☉

Metallicity [Fe/H]

-0.23

Extended Stellar Properties

Surface gravity (log g)

4.450 dex

Stellar density

3.144 g/cm³

Systemic radial velocity

57.38 km/s

Rotational v·sin i

1.50 km/s

Metallicity ratio

[Fe/H]

Distance

62.70 parsec

Light-years 204.50 ly

V-band magnitude

11.96 mag

Voyager-speed travel 3,606,296 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

15.921 mas

Total Proper Motion

173.491 mas/yr

PM Right Ascension

149.95 mas/yr

PM Declination

-87.25 mas/yr

Galactic Cartesian (pc)

x = 0.855 · y = 0.110 · z = -0.507

Equatorial (J2000)

RA 7.30201° · Dec -30.45412°

Galactic ℓ, b

357.289° · -84.104°

Ecliptic λ, β

353.254° · -30.571°

HTM-20 index

-1735222970