Key parameters at a glance

A radius of 1.13 Earth radii
A mass of 1.86 Earth masses
Surface gravity around 1.46 g
An orbital period of 3.648 days
Semi-major axis 0.0395 AU
Equilibrium temperature 716 K (443 °C)
Distance from Earth 96.74 light-years
Earth Similarity Index 0.430
Travel time at Voyager 1 speed 1,706,030 years
Almost certainly tidally locked to its host star given the close orbit

2 siblings around GJ 9827

GJ 9827 c shares its host star with 2 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
GJ 9827 b	Super-Earth	1.44	4.28	1.209	1,035	2017
GJ 9827 c this	Rocky Terrestrial	1.13	1.86	3.648	716	2017
GJ 9827 d	Super-Earth	1.98	3.02	6.202	675	2017

GJ 9827 c Planet Profile

Physical Specs

Radius

1.13 R⊕

Radius (Jupiter)

0.101 R♃

Mass

1.86 M⊕

Mass (Jupiter)

0.006 M♃

Density

7.14 g/cm³

Surface Gravity

1.46 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.430

HZ Position Inner

Controversial No

Discovery

Year 2017

Method Transit

Facility K2

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#180of 570

top 31.4%

This planet

1.13R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

TOI-1450 A c 1.13 R⊕ Kepler-250 b 1.13 R⊕ Kepler-887 c 1.13 R⊕

Metric	Earth	GJ 9827 c	Jupiter
Radius (R⊕)	1.00	1.13	11.21
Mass (M⊕)	1.00	1.86	317.83
Density (g/cm³)	5.51	7.14	1.33
Surface Gravity (g)	1.00	1.46	2.53
Insolation (S⊕)	1.00	73.00	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	1.860 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	2.420 M⊕	Lower bound from radial-velocity fitting.
Computed mass	2.421 M⊕	Model-computed mass (e.g. from mass-radius relation).

Star Catalogue Identifiers

HIP

HIP 115752

TIC

TIC 301289516

Gaia DR2

Gaia DR2 2643842302456085888

Gaia DR3

Gaia DR3 2643842302456085888

System

GJ 9827

Percentile among Rocky Terrestrial cohort

Radius 1.130 R⊕ · percentile 66 / cohort 570

Mass 1.860 M⊕ · percentile 77 / cohort 570

Orbital period 3.65 d · percentile 40 / cohort 567

Distance 29.66 pc · percentile 13 / cohort 566

ESI 0.430 · percentile 63 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

3.648 days

Semi-major axis

0.0395 AU

Eccentricity

0.000

Inclination

89.09 °

Year Length

A year here lasts approximately 3.65 Earth days (1.0% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0395 AU.

Transit Fingerprint

Depth

0.036 %

Duration

1.826 h

Impact parameter b

0.230

Rp / R★

0.018870

Transit midpoint (BJD)

2,457,742.2000

Photometric dip

Transit produces a flux drop of 361 ppm lasting ≈ 1.83 h.

Extended Orbital Architecture

Planet / star radius ratio

0.018870

Semi-major axis / stellar radius

14.040

Impact parameter (b)

0.230

RV semi-amplitude (K)

1.060 m/s

Transit mid-time (BJD)

2,457,742.2000

Angular separation (arcsec)

1.33000

Eq. Temperature

716K

(443 °C)

Insolation (S⊕)

73.00

Earth = 1.00

Earth Similarity (ESI)

0.430

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

Niraula et al. 2017

Instrument

Kepler CCD Array

Publication

2017-12

Observation locale

Space

Discovery cohort

Planets confirmed in 2017 at K2 (12 shown).

K2-129 b · Rocky Terrestrial K2-130 b · Super-Earth K2-133 b · Super-Earth K2-128 b · Super-Earth K2-133 c · Super-Earth K2-116 b · Rocky Terrestrial K2-125 b · Sub-Neptune K2-118 b · Sub-Neptune K2-136 d · Super-Earth K2-123 b · Sub-Neptune K2-136 c · Sub-Neptune K2-124 b · Sub-Neptune

Host System: GJ 9827

Spectral Class

K-type orange

Effective Temperature

4,236 K — cooler than the Sun (5,778 K)

Estimated Age

5.46 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.580 R☉

Stellar Mass

0.620 M☉

Metallicity [Fe/H]

-0.29

Extended Stellar Properties

Surface gravity (log g)

4.719 dex

Stellar density

3.970 g/cm³

Systemic radial velocity

31.95 km/s

Rotational v·sin i

1.75 km/s

Rotation period

28.16 days

Activity index (log R'HK)

-5.280

Metallicity ratio

[Fe/H]

Distance

29.66 parsec

Light-years 96.74 ly

V-band magnitude

10.37 mag

Voyager-speed travel 1,706,030 yr

Multi-band Host Photometry — 18 bands

Astrometric Data

Parallax

33.686 mas

Total Proper Motion

433.678 mas/yr

PM Right Ascension

376.02 mas/yr

PM Declination

216.07 mas/yr

Galactic Cartesian (pc)

x = 0.989 · y = -0.143 · z = -0.022

Equatorial (J2000)

RA 351.77178° · Dec -1.28534°

Galactic ℓ, b

81.348° · -57.183°

Ecliptic λ, β

351.932° · 2.082°

HTM-20 index

-676985054