Key parameters at a glance

A radius of 0.84 Earth radii
A mass of 0.46 Earth masses
Surface gravity around 0.66 g
An orbital period of 2.253 days
Semi-major axis 0.0223 AU
Equilibrium temperature 620 K (347 °C)
Distance from Earth 34.64 light-years
Earth Similarity Index 0.491
Travel time at Voyager 1 speed 610,802 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

L 98-59 b is an exoplanet having a size between that of the Earth and Mars and a mass only half that of Venus. It orbits L 98-59, a red dwarf star 34.6 light-years away in the constellation Volans. There are at least 4 other planets in the system: L 98-59 c, d, e, f and the unconfirmed ".06". Its discovery was announced on 27 June 2019 in The Astronomical Journal and in a NASA press release. It was the smallest planet discovered by TESS until the discovery of LHS 1678 b, and was the lowest-mass planet whose mass had been measured using radial velocities until Proxima Centauri d was found in 2022.

Excerpted from Wikipedia · full article

4 siblings around L 98-59

L 98-59 b shares its host star with 4 other confirmed planets. Side-by-side measurements below.

Planet	Type	Radius (R⊕)	Mass (M⊕)	Period (d)	Eq. T (K)	Year
L 98-59 b this	Rocky Terrestrial	0.84	0.46	2.253	620	2019
L 98-59 c	Super-Earth	1.33	2.00	3.691	526	2019
L 98-59 d	Super-Earth	1.63	1.64	7.451	416	2019
L 98-59 e	Super-Earth	1.49	2.82	12.828	347	2021
L 98-59 f	Super-Earth	1.48	2.80	23.064	285	2025

L 98-59 b Planet Profile

Physical Specs

Radius

0.84 R⊕

Radius (Jupiter)

0.075 R♃

Mass

0.46 M⊕

Mass (Jupiter)

0.001 M♃

Density

4.30 g/cm³

Surface Gravity

0.66 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.491

HZ Position Inner

Controversial No

Discovery

Year 2019

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#459of 570

top 80.4%

This planet

0.84R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-450 d 0.84 R⊕ Kepler-1579 b 0.84 R⊕ Kepler-131 c 0.84 R⊕

Metric	Earth	L 98-59 b	Jupiter
Radius (R⊕)	1.00	0.84	11.21
Mass (M⊕)	1.00	0.46	317.83
Density (g/cm³)	5.51	4.30	1.33
Surface Gravity (g)	1.00	0.66	2.53
Insolation (S⊕)	1.00	24.50	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	0.460 M⊕	Direct mass measurement (not derived).

Star Catalogue Identifiers

TIC

TIC 307210830

Gaia DR2

Gaia DR2 5271055243163629056

Gaia DR3

Gaia DR3 5271055243163629056

System

L 98-59

Percentile among Rocky Terrestrial cohort

Radius 0.837 R⊕ · percentile 19 / cohort 570

Mass 0.460 M⊕ · percentile 15 / cohort 570

Orbital period 2.25 d · percentile 25 / cohort 567

Distance 10.62 pc · percentile 5 / cohort 566

ESI 0.491 · percentile 69 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

2.253 days

Semi-major axis

0.0223 AU

Eccentricity

0.031

Inclination

88.08 °

Year Length

A year here lasts approximately 2.25 Earth days (0.6% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0223 AU.

Transit Fingerprint

Depth

0.059 %

Duration

1.010 h

Impact parameter b

0.510

Rp / R★

0.025804

Transit midpoint (BJD)

2,458,366.1706

Photometric dip

Transit produces a flux drop of 589 ppm lasting ≈ 1.01 h.

Extended Orbital Architecture

Planet / star radius ratio

0.025804

Semi-major axis / stellar radius

15.288

Impact parameter (b)

0.510

RV semi-amplitude (K)

0.360 m/s

Transit mid-time (BJD)

2,458,366.1706

Long. of periastron (ω)

192.00°

Angular separation (arcsec)

2.10000

Eq. Temperature

620K

(347 °C)

Insolation (S⊕)

24.50

Earth = 1.00

Earth Similarity (ESI)

0.491

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

Kostov et al. 2019

Instrument

TESS CCD Array

Publication

2019-07

Observation locale

Space

Discovery cohort

Planets confirmed in 2019 at Transiting Exoplanet Survey Satellite (TESS) (12 shown).

LP 791-18 c · Sub-Neptune LTT 1445 A b · Super-Earth TOI-270 d · Sub-Neptune L 98-59 d · Super-Earth GJ 357 b · Rocky Terrestrial GJ 143 b · Sub-Neptune HD 23472 c · Super-Earth L 98-59 c · Super-Earth LP 791-18 b · Rocky Terrestrial TOI-270 c · Sub-Neptune HD 23472 b · Sub-Neptune TOI-270 b · Super-Earth

Host System: L 98-59

Spectral Class

M-type red dwarf

Effective Temperature

3,415 K — cooler than the Sun (5,778 K)

Estimated Age

4.94 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.316 R☉

Stellar Mass

0.292 M☉

Metallicity [Fe/H]

-0.46

Extended Stellar Properties

Surface gravity (log g)

4.910 dex

Stellar density

13.000 g/cm³

Systemic radial velocity

-5.68 km/s

Rotational v·sin i

0.00 km/s

Rotation period

77.50 days

Metallicity ratio

[Fe/H]

Distance

10.62 parsec

Light-years 34.64 ly

V-band magnitude

11.69 mag

Voyager-speed travel 610,802 yr

Multi-band Host Photometry — 13 bands

Astrometric Data

Parallax

94.139 mas

Total Proper Motion

353.413 mas/yr

PM Right Ascension

94.77 mas/yr

PM Declination

-340.47 mas/yr

Galactic Cartesian (pc)

x = -0.209 · y = 0.304 · z = -0.929

Equatorial (J2000)

RA 124.53286° · Dec -68.31447°

Galactic ℓ, b

281.817° · -17.593°

Ecliptic λ, β

203.326° · -76.814°

HTM-20 index

1081502068

Wikipedia → Image: Wikimedia Commons · Martin Vargic / Halcyon Maps Based on public domain imagery… · CC BY 3.0