Key parameters at a glance

A radius of 4.91 Earth radii
A mass of 21.40 Earth masses
Surface gravity around 0.89 g
An orbital period of 241.800 days
Semi-major axis 0.6570 AU
Distance from Earth 66.95 light-years
Earth Similarity Index 0.482
Travel time at Voyager 1 speed 1,180,641 years

1 sibling around GJ 328

GJ 328 c shares its host star with 1 other confirmed planet. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
GJ 328 c this	Neptune-like	4.91	21.40	241.800	—	2023
GJ 328 b	Gas Giant	13.30	797.75	3,771.000	—	2013

GJ 328 c Planet Profile

Physical Specs

Radius

4.91 R⊕

Radius (Jupiter)

0.438 R♃

Mass

21.40 M⊕

Mass (Jupiter)

0.067 M♃

Density

0.99 g/cm³

Surface Gravity

0.89 g (Earth)

Classification

Planet Type

Neptune-like

ESI Score 0.482

HZ Position Unknown

Controversial No

Discovery

Year 2023

Method Radial Velocity

Facility Roque de los Muchachos Observatory

Telescope 3.58 m Telescopio Nazionale Galileo

Size rank in cohort

Rank by radius

#397of 574

top 69.0%

This planet

4.91R⊕

Neptune-like median

6.39R⊕

Nearest-size peers

TOI-5678 b 4.91 R⊕ HIP 41378 e 4.92 R⊕ Kepler-27 c 4.90 R⊕

Metric	Earth	GJ 328 c	Jupiter
Radius (R⊕)	1.00	4.91	11.21
Mass (M⊕)	1.00	21.40	317.83
Density (g/cm³)	5.51	0.99	1.33
Surface Gravity (g)	1.00	0.89	2.53
Insolation (S⊕)	1.00	—	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	21.400 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HIP

HIP 43790

TIC

TIC 265373654

Gaia DR2

Gaia DR2 577602496345490176

Gaia DR3

Gaia DR3 577602496345490176

System

GJ 328

Percentile among Neptune-like cohort

Radius 4.910 R⊕ · percentile 31 / cohort 574

Mass 21.400 M⊕ · percentile 33 / cohort 574

Orbital period 241.80 d · percentile 92 / cohort 524

Distance 20.53 pc · percentile 6 / cohort 572

ESI 0.482 · percentile 87 / cohort 574

Orbit & Habitability

Orbital Dynamics

Period

241.800 days

Semi-major axis

0.6570 AU

Eccentricity

—

Inclination

— °

Year Length

A year here lasts approximately 241.80 Earth days (66.2% of a terrestrial year) at a mean orbital distance of 0.6570 AU.

Eq. Temperature

—

Insolation (S⊕)

—

Earth = 1.00

Earth Similarity (ESI)

0.482

0 = alien, 1 = Earth-identical

Discovery Paper

Primary reference

Pinamonti et al. 2023

Instrument

HARPS-N Spectrograph

Publication

2023-09

Observation locale

Ground

Discovery cohort

Planets confirmed in 2023 at Roque de los Muchachos Observatory (7 shown).

GJ 9404 b · Sub-Neptune Kepler-10 d · Sub-Neptune HD 99492 c · Neptune-like K2-312 c · Gas Giant Kepler-454 d · Gas Giant TOI-4010 e · Gas Giant Kepler-68 e · Gas Giant

Host System: GJ 328

Spectral Class

M-type red dwarf

Effective Temperature

3,897 K — cooler than the Sun (5,778 K)

Estimated Age

—

Stellar Radius

0.630 R☉

Stellar Mass

0.650 M☉

Metallicity [Fe/H]

-0.06

Extended Stellar Properties

Surface gravity (log g)

4.640 dex

Stellar density

3.211 g/cm³

Activity index (log R'HK)

-4.679

Metallicity ratio

[Fe/H]

Distance

20.53 parsec

Light-years 66.95 ly

V-band magnitude

9.99 mag

Voyager-speed travel 1,180,641 yr

Multi-band Host Photometry — 17 bands

Astrometric Data

Parallax

48.688 mas

Total Proper Motion

1,046.927 mas/yr

PM Right Ascension

44.75 mas/yr

PM Declination

-1,045.97 mas/yr

Galactic Cartesian (pc)

x = -0.692 · y = 0.722 · z = 0.027

Equatorial (J2000)

RA 133.78195° · Dec 1.54200°

Galactic ℓ, b

226.710° · 27.999°

Ecliptic λ, β

135.785° · -15.212°

HTM-20 index

405678230