Key parameters at a glance

A radius of 0.69 Earth radii
A mass of 0.35 Earth masses
Surface gravity around 0.75 g
An orbital period of 0.860 days
Semi-major axis 0.0124 AU
Equilibrium temperature 830 K (557 °C)
Distance from Earth 64.83 light-years
Earth Similarity Index 0.368
Travel time at Voyager 1 speed 1,143,347 years
Almost certainly tidally locked to its host star given the close orbit

2 siblings around LHS 1678

LHS 1678 b 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
LHS 1678 b this	Rocky Terrestrial	0.69	0.35	0.860	830	2021
LHS 1678 c	Rocky Terrestrial	0.94	1.40	3.694	511	2021
LHS 1678 d	Rocky Terrestrial	0.98	0.91	4.965	463	2024

LHS 1678 b Planet Profile

Physical Specs

Radius

0.69 R⊕

Radius (Jupiter)

0.061 R♃

Mass

0.35 M⊕

Mass (Jupiter)

0.001 M♃

Density

6.00 g/cm³

Surface Gravity

0.75 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.368

HZ Position Inner

Controversial No

Discovery

Year 2021

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#535of 570

top 93.7%

This planet

0.69R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-141 b 0.69 R⊕ K2-116 b 0.69 R⊕ Kepler-1558 b 0.68 R⊕

Metric	Earth	LHS 1678 b	Jupiter
Radius (R⊕)	1.00	0.69	11.21
Mass (M⊕)	1.00	0.35	317.83
Density (g/cm³)	5.51	6.00	1.33
Surface Gravity (g)	1.00	0.75	2.53
Insolation (S⊕)	1.00	94.30	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.350 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 77156829

Gaia DR2

Gaia DR2 4864160624337973248

Gaia DR3

Gaia DR3 4864160624337973248

System

LHS 1678

Percentile among Rocky Terrestrial cohort

Radius 0.685 R⊕ · percentile 6 / cohort 570

Mass 0.350 M⊕ · percentile 9 / cohort 570

Orbital period 0.86 d · percentile 9 / cohort 567

Distance 19.88 pc · percentile 9 / cohort 566

ESI 0.368 · percentile 53 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

0.860 days

Semi-major axis

0.0124 AU

Eccentricity

0.033

Inclination

88.53 °

Year Length

A year here lasts roughly 20.6 hours long on a nearly circular orbit at a mean orbital distance of 0.0124 AU.

Transit Fingerprint

Depth

0.072 %

Duration

0.801 h

Impact parameter b

0.210

Rp / R★

0.019050

Transit midpoint (BJD)

2,458,998.1555

Photometric dip

Transit produces a flux drop of 720 ppm lasting ≈ 0.80 h.

Extended Orbital Architecture

Planet / star radius ratio

0.019050

Semi-major axis / stellar radius

8.080

Impact parameter (b)

0.210

Transit mid-time (BJD)

2,458,998.1555

Long. of periastron (ω)

-23.00°

Angular separation (arcsec)

0.62300

Eq. Temperature

830K

(557 °C)

Insolation (S⊕)

94.30

Earth = 1.00

Earth Similarity (ESI)

0.368

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.

Discovery Paper

Primary reference

Silverstein et al. 2022

Instrument

TESS CCD Array

Publication

2022-04

Observation locale

Space

Discovery cohort

Planets confirmed in 2021 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

TOI-2257 b · Sub-Neptune TOI-2285 b · Super-Earth TOI-1231 b · Sub-Neptune AU Mic c · Sub-Neptune LHS 1678 c · Rocky Terrestrial LHS 1478 b · Rocky Terrestrial TOI-2406 b · Sub-Neptune HD 207897 b · Sub-Neptune TOI-269 b · Sub-Neptune TIC 172900988 b · Gas Giant TOI-178 g · Sub-Neptune TOI-2076 d · Sub-Neptune

Host System: LHS 1678

Spectral Class

M-type red dwarf

Effective Temperature

3,490 K — cooler than the Sun (5,778 K)

Estimated Age

7.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.329 R☉

Stellar Mass

0.345 M☉

Metallicity [Fe/H]

—

Extended Stellar Properties

Surface gravity (log g)

4.890 dex

Stellar density

13.900 g/cm³

Systemic radial velocity

11.47 km/s

Rotational v·sin i

0.53 km/s

Rotation period

64.00 days

Activity index (log R'HK)

-6.087

Distance

19.88 parsec

Light-years 64.83 ly

V-band magnitude

12.60 mag

Voyager-speed travel 1,143,347 yr

Multi-band Host Photometry — 6 bands

Astrometric Data

Parallax

50.277 mas

Total Proper Motion

996.945 mas/yr

PM Right Ascension

239.41 mas/yr

PM Declination

-967.77 mas/yr

Galactic Cartesian (pc)

x = 0.286 · y = 0.713 · z = -0.640

Equatorial (J2000)

RA 68.17899° · Dec -39.79087°

Galactic ℓ, b

243.298° · -42.917°

Ecliptic λ, β

54.461° · -60.566°

HTM-20 index

1504924265