Key parameters at a glance
- A radius of 7.16 Earth radii
- A mass of 43.86 Earth masses
- Surface gravity around 0.85 g
- An orbital period of 18.388 days
- Semi-major axis 0.1528 AU
- Equilibrium temperature 1,027 K (754 °C)
- Distance from Earth 250.82 light-years
- Earth Similarity Index 0.155
- Travel time at Voyager 1 speed 4,423,265 years
TOI-257 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#191of 574
top 33.1%
This planet
7.16R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | TOI-257 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 7.16 | 11.21 |
| Mass (M⊕) | 1.00 | 43.86 | 317.83 |
| Density (g/cm³) | 5.51 | 0.65 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.85 | 2.53 |
| Insolation (S⊕) | 1.00 | 186.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 43.860 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
HD
HD 19916
TIC
TIC 200723869
Gaia DR2
Gaia DR2 4747624104168195072
Gaia DR3
Gaia DR3 4747624104168195072
System
TOI-257
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 18.39 Earth days (5.0% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1528 AU.
Transit Fingerprint
Depth
0.124 %
Duration
6.485 h
Impact parameter b
0.643
Rp / R★
0.035210
Transit midpoint (BJD)
2,458,385.7601
Photometric dip
Transit produces a flux drop of 1,240 ppm lasting ≈ 6.49 h.
Extended Orbital Architecture
Planet / star radius ratio
0.035210
Semi-major axis / stellar radius
17.600
Impact parameter (b)
0.643
RV semi-amplitude (K)
8.500 m/s
Transit mid-time (BJD)
2,458,385.7601
Angular separation (arcsec)
1.99000
Eq. Temperature
1,027K
(754 °C)
Insolation (S⊕)
186.00
Earth = 1.00
Earth Similarity (ESI)
0.155
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched.
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
Addison et al. 2021Instrument
TESS CCD Array
Publication
2021-04
Observation locale
Space
Discovery cohort
Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
Host System: TOI-257
Spectral Class
F-type yellow-white
Effective Temperature
6,095 K — hotter than the Sun (5,778 K)
Estimated Age
—
Stellar Radius
1.867 R☉
Stellar Mass
1.407 M☉
Metallicity [Fe/H]
0.18
Extended Stellar Properties
Surface gravity (log g)
4.044 dex
Stellar density
0.305 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
12.975 mas
Total Proper Motion
101.813 mas/yr
PM Right Ascension
97.91 mas/yr
PM Declination
27.91 mas/yr
Galactic Cartesian (pc)
x = 0.427 · y = 0.466 · z = -0.775
Equatorial (J2000)
RA 47.51726° · Dec -50.83226°
Galactic ℓ, b
264.529° · -54.676°
Ecliptic λ, β
15.578° · -63.715°
HTM-20 index
-471174425
Similar Worlds
TOI-3071 b
Neptune-like · F-type yellow-white
Radius 7.16 R⊕ · 1,582.6 ly
Kepler-79 d
Neptune-like · F-type yellow-white
Radius 7.16 R⊕ · 3,329.1 ly
Kepler-1085 b
Neptune-like · F-type yellow-white
Radius 7.22 R⊕ · 4,450.5 ly
Kepler-51 b
Neptune-like · F-type yellow-white
Radius 7.10 R⊕ · 2,556.5 ly
WASP-166 b
Neptune-like · F-type yellow-white
Radius 7.06 R⊕ · 372.4 ly
HD 151450 b
Neptune-like · F-type yellow-white
Radius 6.94 R⊕ · 142.2 ly