Key parameters at a glance
- A radius of 2.19 Earth radii
- A mass of 5.45 Earth masses
- Surface gravity around 1.13 g
- An orbital period of 35.189 days
- Semi-major axis 0.1450 AU
- Equilibrium temperature 256 K (-17 °C)
- Distance from Earth 188.49 light-years
- Earth Similarity Index 0.742
- Travel time at Voyager 1 speed 3,324,006 years
- Almost certainly tidally locked to its host star given the close orbit
Context from the literature
TOI-2257 b is an extremely eccentric (0.496) exoplanet in or near the circumstellar habitable zone of the star TOI-2257, 188 light-years away. It is likely a sub-Neptune exoplanet, with a mass of 5.71 Mearth and a radius of 2.19 Rearth. As a small planet in the habitable zone, it is included in the Planetary Habitability Laboratory's list of potentially habitable exoplanets.
Excerpted from Wikipedia · full article
TOI-2257 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1690of 1978
top 85.4%
This planet
2.19R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | TOI-2257 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.19 | 11.21 |
| Mass (M⊕) | 1.00 | 5.45 | 317.83 |
| Density (g/cm³) | 5.51 | 2.84 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.13 | 2.53 |
| Insolation (S⊕) | 1.00 | 0.67 | 0.037 |
Star Catalogue Identifiers
TIC
TIC 198485881
Gaia DR2
Gaia DR2 1716345832872291968
Gaia DR3
Gaia DR3 1716345832872291968
System
TOI-2257
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 35.19 Earth days (9.6% of a terrestrial year) on a highly eccentric trajectory at a mean orbital distance of 0.1450 AU.
Transit Fingerprint
Depth
0.413 %
Duration
3.846 h
Impact parameter b
0.374
Rp / R★
0.064230
Transit midpoint (BJD)
2,459,007.9795
Photometric dip
Transit produces a flux drop of 4,130 ppm lasting ≈ 3.85 h.
Extended Orbital Architecture
Planet / star radius ratio
0.064230
Impact parameter (b)
0.374
Transit mid-time (BJD)
2,459,007.9795
Long. of periastron (ω)
-101.67°
Angular separation (arcsec)
2.51000
Eq. Temperature
256K
(-17 °C)
Insolation (S⊕)
0.67
Earth = 1.00
Earth Similarity (ESI)
0.742
0 = alien, 1 = Earth-identical
Within the conservative habitable zone — surface water would be frozen. Close-orbiting tidally-locked around a cool host.
Discovery Paper
Primary reference
Schanche et al. 2022Instrument
TESS CCD Array
Publication
2022-01
Observation locale
Space
Discovery cohort
Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
Host System: TOI-2257
Spectral Class
M-type red dwarf
Effective Temperature
3,430 K — cooler than the Sun (5,778 K)
Estimated Age
—
Stellar Radius
0.313 R☉
Stellar Mass
0.328 M☉
Metallicity [Fe/H]
-0.27
Extended Stellar Properties
Surface gravity (log g)
4.971 dex
Stellar density
15.800 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
17.275 mas
Total Proper Motion
47.780 mas/yr
PM Right Ascension
-35.99 mas/yr
PM Declination
31.42 mas/yr
Galactic Cartesian (pc)
x = -0.207 · y = -0.054 · z = 0.977
Equatorial (J2000)
RA 194.73961° · Dec 77.66172°
Galactic ℓ, b
122.412° · 39.459°
Ecliptic λ, β
121.384° · 66.623°
HTM-20 index
-1627633403
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