Key parameters at a glance
- A radius of 2.09 Earth radii
- A mass of 4.50 Earth masses
- Surface gravity around 1.03 g
- An orbital period of 16.341 days
- Semi-major axis 0.1270 AU
- Equilibrium temperature 781 K (507 °C)
- Distance from Earth 119.30 light-years
- Earth Similarity Index 0.342
- Travel time at Voyager 1 speed 2,103,879 years
TOI-2128 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1843of 1978
top 93.1%
This planet
2.09R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | TOI-2128 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.09 | 11.21 |
| Mass (M⊕) | 1.00 | 4.50 | 317.83 |
| Density (g/cm³) | 5.51 | 2.68 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.03 | 2.53 |
| Insolation (S⊕) | 1.00 | 86.23 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 4.500 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
HIP
HIP 83827
TIC
TIC 21832928
Gaia DR2
Gaia DR2 1334288219648212352
Gaia DR3
Gaia DR3 1334288219648212352
System
TOI-2128
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 16.34 Earth days (4.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1270 AU.
Transit Fingerprint
Depth
0.037 %
Duration
4.698 h
Impact parameter b
0.375
Rp / R★
0.017138
Transit midpoint (BJD)
2,458,987.2663
Photometric dip
Transit produces a flux drop of 372 ppm lasting ≈ 4.70 h.
Extended Orbital Architecture
Planet / star radius ratio
0.017138
Impact parameter (b)
0.375
RV semi-amplitude (K)
1.100 m/s
Transit mid-time (BJD)
2,458,987.2663
Long. of periastron (ω)
90.00°
Angular separation (arcsec)
3.47000
Eq. Temperature
781K
(507 °C)
Insolation (S⊕)
86.23
Earth = 1.00
Earth Similarity (ESI)
0.342
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
Polanski et al. 2024Instrument
TESS CCD Array
Publication
2024-06
Observation locale
Space
Discovery cohort
Planets confirmed in 2024 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).
Host System: TOI-2128
Spectral Class
G-type yellow (Sun-like)
Effective Temperature
5,968 K — hotter than the Sun (5,778 K)
Estimated Age
4.70 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
1.117 R☉
Stellar Mass
1.025 M☉
Metallicity [Fe/H]
-0.07
Extended Stellar Properties
Surface gravity (log g)
4.349 dex
Stellar density
1.023 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 11 bands
Astrometric Data
Parallax
27.310 mas
Total Proper Motion
167.400 mas/yr
PM Right Ascension
-162.01 mas/yr
PM Declination
-42.12 mas/yr
Galactic Cartesian (pc)
x = -0.191 · y = -0.825 · z = 0.531
Equatorial (J2000)
RA 256.98180° · Dec 32.10530°
Galactic ℓ, b
54.706° · 34.846°
Ecliptic λ, β
250.726° · 54.677°
HTM-20 index
1757413098
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