Key parameters at a glance
- A radius of 11.15 Earth radii
- A mass of 62.61 Earth masses
- Surface gravity around 0.50 g
- An orbital period of 5.508 days
- Semi-major axis 0.0559 AU
- Equilibrium temperature 852 K (579 °C)
- Distance from Earth 526.42 light-years
- Earth Similarity Index 0.142
- Travel time at Voyager 1 speed 9,283,342 years
- Almost certainly tidally locked to its host star given the close orbit
HAT-P-18 b Planet Profile
Physical Specs
Classification
Planet Type
Gas Giant
Discovery
Size rank in cohort
Rank by radius
#1642of 1771
top 92.7%
This planet
11.15R⊕
Gas Giant median
13.52R⊕
Nearest-size peers
| Metric | Earth | HAT-P-18 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 11.15 | 11.21 |
| Mass (M⊕) | 1.00 | 62.61 | 317.83 |
| Density (g/cm³) | 5.51 | 0.25 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.50 | 2.53 |
| Insolation (S⊕) | 1.00 | 82.24 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 62.610 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
TIC
TIC 21744120
Gaia DR2
Gaia DR2 1334573817793362560
Gaia DR3
Gaia DR3 1334573817793362560
System
HAT-P-18
Percentile among Gas Giant cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 5.51 Earth days (1.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0559 AU.
Transit Fingerprint
Depth
2.158 %
Duration
2.714 h
Impact parameter b
0.324
Rp / R★
0.136500
Transit midpoint (BJD)
2,454,715.0217
Photometric dip
Transit produces a flux drop of 21,585 ppm lasting ≈ 2.71 h.
Extended Orbital Architecture
Planet / star radius ratio
0.136500
Semi-major axis / stellar radius
16.040
Impact parameter (b)
0.324
RV semi-amplitude (K)
27.100 m/s
Transit mid-time (BJD)
2,454,715.0217
Long. of periastron (ω)
120.00°
Sky-projected obliquity (λ)
132.00°
Angular separation (arcsec)
0.34600
Eq. Temperature
852K
(579 °C)
Insolation (S⊕)
82.24
Earth = 1.00
Earth Similarity (ESI)
0.142
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.
Discovery Paper
Primary reference
Hartman et al. 2011Instrument
2K CCD Sensor
Publication
2011-01
Observation locale
Ground
Discovery cohort
Planets confirmed in 2010 at HATNet (12 shown).
Host System: HAT-P-18
Spectral Class
K-type orange
Effective Temperature
4,803 K — cooler than the Sun (5,778 K)
Estimated Age
12.40 Gyr — older than the Sun (4.6 Gyr)
Stellar Radius
0.749 R☉
Stellar Mass
0.770 M☉
Metallicity [Fe/H]
0.10
Extended Stellar Properties
Surface gravity (log g)
4.570 dex
Stellar density
2.940 g/cm³
Systemic radial velocity
-11.92 km/s
Rotational v·sin i
0.50 km/s
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 16 bands
Astrometric Data
Parallax
6.167 mas
Total Proper Motion
39.296 mas/yr
PM Right Ascension
-14.07 mas/yr
PM Declination
-36.69 mas/yr
Galactic Cartesian (pc)
x = -0.198 · y = -0.815 · z = 0.545
Equatorial (J2000)
RA 256.34638° · Dec 33.01233°
Galactic ℓ, b
55.652° · 35.562°
Ecliptic λ, β
249.549° · 55.487°
HTM-20 index
-314841901
Observation Record
RV measurements
1
Transmission spectra
5
Emission spectra
4
Archive notes
1
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