Key parameters at a glance
- A radius of 2.94 Earth radii
- A mass of 4.40 Earth masses
- Surface gravity around 0.51 g
- An orbital period of 20.717 days
- Semi-major axis 0.1275 AU
- Equilibrium temperature 470 K (197 °C)
- Distance from Earth 204.50 light-years
- Earth Similarity Index 0.439
- Travel time at Voyager 1 speed 3,606,296 years
- Almost certainly tidally locked to its host star given the close orbit
Context from the literature
TOI-178 is a planetary system in the constellation Sculptor around which six planets have been observed, at least five of which orbit in a chain of Laplace resonances, which constitute one of the longest chains yet discovered in a system of planets. The system also has unusual variations in the densities among the planets.
Excerpted from Wikipedia · full article
5 siblings around TOI-178
TOI-178 g 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 | 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 this | Sub-Neptune | 2.94 | 4.40 | 20.717 | 470 | 2021 |
TOI-178 g Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#581of 1978
top 29.3%
This planet
2.94R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | TOI-178 g | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.94 | 11.21 |
| Mass (M⊕) | 1.00 | 4.40 | 317.83 |
| Density (g/cm³) | 5.51 | 0.96 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.51 | 2.53 |
| Insolation (S⊕) | 1.00 | 19.50 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 4.400 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 Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 20.72 Earth days (5.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1275 AU.
Transit Fingerprint
Depth
0.166 %
Duration
2.167 h
Impact parameter b
0.855
Rp / R★
0.040750
Transit midpoint (BJD)
2,458,748.0302
Photometric dip
Transit produces a flux drop of 1,661 ppm lasting ≈ 2.17 h.
Extended Orbital Architecture
Planet / star radius ratio
0.040750
Semi-major axis / stellar radius
42.130
Impact parameter (b)
0.855
RV semi-amplitude (K)
1.300 m/s
Transit mid-time (BJD)
2,458,748.0302
Long. of periastron (ω)
-44.00°
Angular separation (arcsec)
2.03000
Eq. Temperature
470K
(197 °C)
Insolation (S⊕)
19.50
Earth = 1.00
Earth Similarity (ESI)
0.439
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.
Radial velocity
Stellar wobble has been measured spectroscopically.
Transit timing variations
Gravitational interactions from neighbours have been detected.
Discovery Paper
Primary reference
Leleu et al. 2021Instrument
TESS CCD Array
Publication
2021-05
Observation locale
Space
Discovery cohort
Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
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]
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
Similar Worlds
TOI-815 b
Sub-Neptune · K-type orange
Radius 2.94 R⊕ · 194.8 ly
Kepler-1086 c
Sub-Neptune · K-type orange
Radius 2.94 R⊕ · 1,520.2 ly
Kepler-1731 b
Sub-Neptune · K-type orange
Radius 2.93 R⊕ · 554.3 ly
K2-266 d
Sub-Neptune · K-type orange
Radius 2.93 R⊕ · 253.0 ly
HD 15906 c
Sub-Neptune · K-type orange
Radius 2.93 R⊕ · 148.6 ly
TOI-125 d
Sub-Neptune · K-type orange
Radius 2.93 R⊕ · 362.2 ly