Key parameters at a glance
- A radius of 3.08 Earth radii
- A mass of 10.30 Earth masses
- Surface gravity around 1.09 g
- An orbital period of 15.610 days
- Semi-major axis 0.1223 AU
- Equilibrium temperature 950 K (677 °C)
- Distance from Earth 263.38 light-years
- Earth Similarity Index 0.245
- Travel time at Voyager 1 speed 4,644,788 years
TOI-5817 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#448of 1978
top 22.6%
This planet
3.08R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | TOI-5817 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 3.08 | 11.21 |
| Mass (M⊕) | 1.00 | 10.30 | 317.83 |
| Density (g/cm³) | 5.51 | 1.93 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.09 | 2.53 |
| Insolation (S⊕) | 1.00 | 126.86 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 10.300 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
HD
HD 204660
HIP
HIP 106097
TIC
TIC 418604868
Gaia DR2
Gaia DR2 1790807028049001600
Gaia DR3
Gaia DR3 1790807028049001600
System
TOI-5817
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 15.61 Earth days (4.3% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.1223 AU.
Transit Fingerprint
Depth
0.047 %
Duration
6.000 h
Impact parameter b
0.410
Rp / R★
0.019800
Transit midpoint (BJD)
2,459,799.3065
Photometric dip
Transit produces a flux drop of 467 ppm lasting ≈ 6.00 h.
Extended Orbital Architecture
Planet / star radius ratio
0.019800
Semi-major axis / stellar radius
18.440
Impact parameter (b)
0.410
RV semi-amplitude (K)
2.690 m/s
Transit mid-time (BJD)
2,459,799.3065
Angular separation (arcsec)
1.51000
Eq. Temperature
950K
(677 °C)
Insolation (S⊕)
126.86
Earth = 1.00
Earth Similarity (ESI)
0.245
0 = alien, 1 = Earth-identical
Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.
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
Naponiello et al. 2025Instrument
TESS CCD Array
Publication
2025-05
Observation locale
Space
Discovery cohort
Planets confirmed in 2025 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
Host System: TOI-5817
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,770 K — cooler than the Sun (5,778 K)
Estimated Age
9.70 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.427 R☉
Stellar Mass
0.970 M☉
Metallicity [Fe/H]
-0.24
Extended Stellar Properties
Surface gravity (log g)
4.120 dex
Stellar density
0.470 g/cm³
Rotational v·sin i
1.20 km/s
Activity index (log R'HK)
-4.950
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
12.355 mas
Total Proper Motion
90.425 mas/yr
PM Right Ascension
-10.36 mas/yr
PM Declination
-89.83 mas/yr
Galactic Cartesian (pc)
x = 0.737 · y = -0.568 · z = 0.366
Equatorial (J2000)
RA 322.37780° · Dec 21.47453°
Galactic ℓ, b
72.624° · -21.105°
Ecliptic λ, β
332.995° · 34.184°
HTM-20 index
-745331673
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