Key parameters at a glance

A radius of 2.59 Earth radii
A mass of 7.24 Earth masses
Surface gravity around 1.08 g
An orbital period of 16.458 days
Semi-major axis 0.1244 AU
Equilibrium temperature 644 K (371 °C)
Distance from Earth 2,608.27 light-years
Earth Similarity Index 0.387
Travel time at Voyager 1 speed 45,996,773 years

Kepler-1821 b Planet Profile

Physical Specs

Radius

2.59 R⊕

Radius (Jupiter)

0.231 R♃

Mass

7.24 M⊕

Mass (Jupiter)

0.023 M♃

Density

2.28 g/cm³

Surface Gravity

1.08 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.387

HZ Position Inner

Controversial No

Discovery

Year 2021

Method Transit

Facility Kepler

Telescope 0.95 m Kepler Telescope

Size rank in cohort

Rank by radius

#1041of 1978

top 52.6%

This planet

2.59R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

K2-110 b 2.59 R⊕ Kepler-194 c 2.59 R⊕ Kepler-265 e 2.59 R⊕

Metric	Earth	Kepler-1821 b	Jupiter
Radius (R⊕)	1.00	2.59	11.21
Mass (M⊕)	1.00	7.24	317.83
Density (g/cm³)	5.51	2.28	1.33
Surface Gravity (g)	1.00	1.08	2.53
Insolation (S⊕)	1.00	40.61	0.037

Star Catalogue Identifiers

TIC

TIC 27187386

Gaia DR2

Gaia DR2 2135051371246744960

Gaia DR3

Gaia DR3 2135051371246744960

System

Kepler-1821

Percentile among Sub-Neptune cohort

Radius 2.592 R⊕ · percentile 47 / cohort 1978

Mass 7.240 M⊕ · percentile 44 / cohort 1978

Orbital period 16.46 d · percentile 55 / cohort 1946

Distance 799.70 pc · percentile 65 / cohort 1975

ESI 0.387 · percentile 50 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

16.458 days

Semi-major axis

0.1244 AU

Eccentricity

0.000

Inclination

89.90 °

Year Length

A year here lasts approximately 16.46 Earth days (4.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.1244 AU.

Transit Fingerprint

Depth

0.044 %

Duration

1.821 h

Impact parameter b

0.316

Rp / R★

0.020687

Transit midpoint (BJD)

2,454,967.0186

Photometric dip

Transit produces a flux drop of 436 ppm lasting ≈ 1.82 h.

Extended Orbital Architecture

Planet / star radius ratio

0.020687

Semi-major axis / stellar radius

64.900

Impact parameter (b)

0.316

Transit mid-time (BJD)

2,454,967.0186

Angular separation (arcsec)

0.15600

Eq. Temperature

644K

(371 °C)

Insolation (S⊕)

40.61

Earth = 1.00

Earth Similarity (ESI)

0.387

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the surface is too hot to retain surface water.

Detection Signatures

Transit photometry

A transit dip has been observed from at least one telescope.

Transit timing variations

Gravitational interactions from neighbours have been detected.

Discovery Paper

Primary reference

Valizadegan et al. 2022

Instrument

Kepler CCD Array

Publication

2022-02

Observation locale

Space

Discovery cohort

Planets confirmed in 2021 at Kepler (12 shown).

Kepler-1816 b · Super-Earth Kepler-1705 c · Sub-Neptune Kepler-1948 b · Rocky Terrestrial Kepler-196 d · Sub-Neptune Kepler-1853 b · Super-Earth Kepler-1840 b · Sub-Neptune Kepler-1881 b · Sub-Neptune Kepler-1858 b · Sub-Neptune Kepler-1874 b · Sub-Neptune Kepler-1802 c · Sub-Neptune Kepler-1749 b · Super-Earth Kepler-1849 b · Sub-Neptune

Host System: Kepler-1821

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,475 K — cooler than the Sun (5,778 K)

Estimated Age

0.40 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

0.884 R☉

Stellar Mass

0.946 M☉

Metallicity [Fe/H]

0.14

Extended Stellar Properties

Surface gravity (log g)

4.521 dex

Stellar density

19.061 g/cm³

Metallicity ratio

[Fe/H]

Distance

799.70 parsec

Light-years 2,608.27 ly

V-band magnitude

14.80 mag

Voyager-speed travel 45,996,773 yr

Multi-band Host Photometry — 16 bands

Astrometric Data

Parallax

1.222 mas

Total Proper Motion

4.430 mas/yr

PM Right Ascension

1.60 mas/yr

PM Declination

4.13 mas/yr

Galactic Cartesian (pc)

x = 0.268 · y = -0.586 · z = 0.765

Equatorial (J2000)

RA 294.52546° · Dec 49.87248°

Galactic ℓ, b

82.467° · 13.454°

Ecliptic λ, β

318.843° · 69.188°

HTM-20 index

-487688632