Key parameters at a glance

A radius of 9.25 Earth radii
A mass of 84.86 Earth masses
Surface gravity around 0.99 g
An orbital period of 4.640 days
Semi-major axis 0.0523 AU
Equilibrium temperature 1,082 K (809 °C)
Distance from Earth 832.37 light-years
Earth Similarity Index 0.135
Travel time at Voyager 1 speed 14,678,839 years

HAT-P-38 b Planet Profile

Physical Specs

Radius

9.25 R⊕

Radius (Jupiter)

0.825 R♃

Mass

84.86 M⊕

Mass (Jupiter)

0.267 M♃

Density

0.59 g/cm³

Surface Gravity

0.99 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.135

HZ Position Inner

Controversial No

Discovery

Year 2012

Method Transit

Facility HATNet

Telescope Canon 200mm f/1.8L

Size rank in cohort

Rank by radius

#64of 574

top 11.0%

This planet

9.25R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

TOI-622 b 9.24 R⊕ Kepler-1981 b 9.23 R⊕ K2-261 b 9.27 R⊕

Metric	Earth	HAT-P-38 b	Jupiter
Radius (R⊕)	1.00	9.25	11.21
Mass (M⊕)	1.00	84.86	317.83
Density (g/cm³)	5.51	0.59	1.33
Surface Gravity (g)	1.00	0.99	2.53
Insolation (S⊕)	1.00	243.03	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	84.857 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 285272237

Gaia DR2

Gaia DR2 324889227693298560

Gaia DR3

Gaia DR3 324889227693298560

System

HAT-P-38

Percentile among Neptune-like cohort

Radius 9.247 R⊕ · percentile 89 / cohort 574

Mass 84.857 M⊕ · percentile 89 / cohort 574

Orbital period 4.64 d · percentile 18 / cohort 524

Distance 255.21 pc · percentile 44 / cohort 572

ESI 0.135 · percentile 8 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

4.640 days

Semi-major axis

0.0523 AU

Eccentricity

0.067

Inclination

88.30 °

Year Length

A year here lasts approximately 4.64 Earth days (1.3% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0523 AU.

Transit Fingerprint

Depth

0.995 %

Duration

3.041 h

Impact parameter b

0.372

Rp / R★

0.091800

Transit midpoint (BJD)

2,455,863.1196

Photometric dip

Transit produces a flux drop of 9,955 ppm lasting ≈ 3.04 h.

Extended Orbital Architecture

Planet / star radius ratio

0.091800

Semi-major axis / stellar radius

12.170

Impact parameter (b)

0.372

RV semi-amplitude (K)

35.400 m/s

Transit mid-time (BJD)

2,455,863.1196

Long. of periastron (ω)

240.00°

Angular separation (arcsec)

0.20500

Eq. Temperature

1,082K

(809 °C)

Insolation (S⊕)

243.03

Earth = 1.00

Earth Similarity (ESI)

0.135

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

Sato et al. 2012

Instrument

2K CCD Sensor

Publication

2012-10

Observation locale

Ground

Discovery cohort

Planets confirmed in 2012 at HATNet (5 shown).

HAT-P-42 b · Gas Giant HAT-P-43 b · Gas Giant HAT-P-39 b · Gas Giant HAT-P-40 b · Gas Giant HAT-P-41 b · Gas Giant

Host System: HAT-P-38

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,330 K — cooler than the Sun (5,778 K)

Estimated Age

10.10 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.923 R☉

Stellar Mass

0.886 M☉

Metallicity [Fe/H]

0.06

Extended Stellar Properties

Surface gravity (log g)

4.450 dex

Stellar density

1.208 g/cm³

Systemic radial velocity

-19.70 km/s

Rotational v·sin i

0.40 km/s

Metallicity ratio

[Fe/H]

Distance

255.21 parsec

Light-years 832.37 ly

V-band magnitude

12.53 mag

Voyager-speed travel 14,678,839 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

3.890 mas

Total Proper Motion

52.357 mas/yr

PM Right Ascension

47.77 mas/yr

PM Declination

-21.43 mas/yr

Galactic Cartesian (pc)

x = 0.690 · y = 0.490 · z = 0.534

Equatorial (J2000)

RA 35.38349° · Dec 32.24604°

Galactic ℓ, b

144.229° · -26.873°

Ecliptic λ, β

43.810° · 17.141°

HTM-20 index

324839884