Key parameters at a glance
- A radius of 21.20 Earth radii
- A mass of 915.35 Earth masses
- Surface gravity around 2.04 g
- An orbital period of 1.481 days
- Semi-major axis 0.0346 AU
- Equilibrium temperature 4,050 K (3777 °C)
- Distance from Earth 666.84 light-years
- Earth Similarity Index 0.021
- Travel time at Voyager 1 speed 11,759,762 years
KELT-9 b Planet Profile
Physical Specs
Classification
Planet Type
Gas Giant
Discovery
Size rank in cohort
Rank by radius
#21of 1771
top 1.1%
This planet
21.20R⊕
Gas Giant median
13.52R⊕
Nearest-size peers
| Metric | Earth | KELT-9 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 21.20 | 11.21 |
| Mass (M⊕) | 1.00 | 915.35 | 317.83 |
| Density (g/cm³) | 5.51 | 0.53 | 1.33 |
| Surface Gravity (g) | 1.00 | 2.04 | 2.53 |
| Insolation (S⊕) | 1.00 | 44,900.00 | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 915.350 M⊕ | Direct mass measurement (not derived). |
Star Catalogue Identifiers
HD
HD 195689
HIP
HIP 101252
TIC
TIC 16740101
Gaia DR2
Gaia DR2 2064327278651198336
Gaia DR3
Gaia DR3 2064327278651198336
System
KELT-9
Percentile among Gas Giant cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 1.48 Earth days (0.4% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0346 AU.
Transit Fingerprint
Depth
0.677 %
Duration
3.916 h
Impact parameter b
0.177
Rp / R★
0.082280
Transit midpoint (BJD)
2,457,095.6857
Photometric dip
Transit produces a flux drop of 6,770 ppm lasting ≈ 3.92 h.
Extended Orbital Architecture
Planet / star radius ratio
0.082280
Semi-major axis / stellar radius
3.153
Impact parameter (b)
0.177
RV semi-amplitude (K)
276.000 m/s
Transit mid-time (BJD)
2,457,095.6857
Long. of periastron (ω)
90.00°
Sky-projected obliquity (λ)
-84.80°
Angular separation (arcsec)
0.16900
Eq. Temperature
4,050K
(3777 °C)
Insolation (S⊕)
44,900.00
Earth = 1.00
Earth Similarity (ESI)
0.021
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.
Orbital-brightness modulation
Host star brightness varies with the planet's orbit.
Discovery Paper
Primary reference
Gaudi et al. 2017Instrument
Apogee 4K CCD Sensor
Publication
2017-06
Observation locale
Ground
Discovery cohort
Planets confirmed in 2017 at KELT-North (3 shown).
Host System: KELT-9
Spectral Class
B-type blue-white
Effective Temperature
10,170 K — hotter than the Sun (5,778 K)
Estimated Age
0.30 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
2.362 R☉
Stellar Mass
2.520 M☉
Metallicity [Fe/H]
-0.03
Extended Stellar Properties
Surface gravity (log g)
4.093 dex
Stellar density
0.270 g/cm³
Systemic radial velocity
-20.57 km/s
Rotational v·sin i
111.40 km/s
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
4.863 mas
Total Proper Motion
27.224 mas/yr
PM Right Ascension
16.73 mas/yr
PM Declination
21.48 mas/yr
Galactic Cartesian (pc)
x = 0.471 · y = -0.605 · z = 0.642
Equatorial (J2000)
RA 307.85990° · Dec 39.93892°
Galactic ℓ, b
78.913° · 0.249°
Ecliptic λ, β
327.475° · 56.077°
HTM-20 index
773485744
Observation Record
Photometric series
1
Transmission spectra
6
Emission spectra
7
Archive notes
1
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