Key parameters at a glance

A radius of 1.11 Earth radii
A mass of 1.40 Earth masses
Surface gravity around 1.14 g
An orbital period of 9.866 days
Semi-major axis 0.0496 AU
Equilibrium temperature 301 K (28 °C)
Distance from Earth 11.01 light-years
Earth Similarity Index 0.949
Travel time at Voyager 1 speed 194,095 years
Almost certainly tidally locked to its host star given the close orbit

Context from the literature

Ross 128 b is a confirmed Earth-sized exoplanet, likely rocky, that is orbiting near the inner edge of the habitable zone of the red dwarf star Ross 128, at a distance of 11.007 light-years from Earth in the constellation of Virgo. The exoplanet was found using a decade's worth of radial velocity data using the European Southern Observatory's HARPS spectrograph at the La Silla Observatory in Chile. Ross 128 b is the nearest exoplanet around a quiet red dwarf, and is considered one of the best candidates for habitability. The planet is only 35% more massive than Earth, receives only 38% more starlight, and is expected to be a temperature suitable for liquid water to exist on the surface, if it has an atmosphere.

Excerpted from Wikipedia · full article

Ross 128 b Planet Profile

Physical Specs

Radius

1.11 R⊕

Radius (Jupiter)

0.099 R♃

Mass

1.40 M⊕

Mass (Jupiter)

0.004 M♃

Density

5.63 g/cm³

Surface Gravity

1.14 g (Earth)

Classification

Planet Type

Rocky Terrestrial

ESI Score 0.949

HZ Position Habitable

Controversial No

Discovery

Year 2017

Method Radial Velocity

Facility La Silla Observatory

Telescope 3.6 m ESO Telescope

Size rank in cohort

Rank by radius

#209of 570

top 36.5%

This planet

1.11R⊕

Rocky Terrestrial median

1.01R⊕

Nearest-size peers

Kepler-124 d 1.11 R⊕ Kepler-327 b 1.11 R⊕ Kepler-333 c 1.11 R⊕

Metric	Earth	Ross 128 b	Jupiter
Radius (R⊕)	1.00	1.11	11.21
Mass (M⊕)	1.00	1.40	317.83
Density (g/cm³)	5.51	5.63	1.33
Surface Gravity (g)	1.00	1.14	2.53
Insolation (S⊕)	1.00	1.38	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Minimum mass (M sin i)	1.400 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HIP

HIP 57548

TIC

TIC 325275315

Gaia DR2

Gaia DR2 3796072592206250624

Gaia DR3

Gaia DR3 3796072592206250624

System

Ross 128

Percentile among Rocky Terrestrial cohort

Radius 1.110 R⊕ · percentile 61 / cohort 570

Mass 1.400 M⊕ · percentile 56 / cohort 570

Orbital period 9.87 d · percentile 77 / cohort 567

Distance 3.37 pc · percentile 1 / cohort 566

ESI 0.949 · percentile 95 / cohort 570

Orbit & Habitability

Orbital Dynamics

Period

9.866 days

Semi-major axis

0.0496 AU

Eccentricity

0.116

Inclination

— °

Year Length

A year here lasts approximately 9.87 Earth days (2.7% of a terrestrial year) on a mildly elliptical path at a mean orbital distance of 0.0496 AU.

Eq. Temperature

301K

(28 °C)

Insolation (S⊕)

1.38

Earth = 1.00

Earth Similarity (ESI)

0.949

0 = alien, 1 = Earth-identical

Within the conservative habitable zone — liquid water is physically possible with adequate atmospheric pressure. Close-orbiting tidally-locked around a cool host.

Discovery Paper

Primary reference

Bonfils et al. 2018

Instrument

HARPS Spectrograph

Publication

2018-05

Observation locale

Ground

Discovery cohort

Planets confirmed in 2017 at La Silla Observatory (12 shown).

GJ 273 c · Rocky Terrestrial GJ 3138 b · Rocky Terrestrial GJ 3323 c · Super-Earth GJ 3323 b · Rocky Terrestrial GJ 273 b · Super-Earth GJ 3293 e · Super-Earth YZ Cet d · Rocky Terrestrial GJ 3138 c · Super-Earth YZ Cet c · Rocky Terrestrial GJ 3293 d · Sub-Neptune YZ Cet b · Rocky Terrestrial GJ 3138 d · Sub-Neptune

Host System: Ross 128

Spectral Class

M-type red dwarf

Effective Temperature

3,192 K — cooler than the Sun (5,778 K)

Estimated Age

5.00 Gyr — older than the Sun (4.6 Gyr)

Stellar Radius

0.197 R☉

Stellar Mass

0.168 M☉

Metallicity [Fe/H]

-0.02

Extended Stellar Properties

Surface gravity (log g)

5.047 dex

Stellar density

27.334 g/cm³

Systemic radial velocity

-30.90 km/s

Rotation period

123.00 days

Metallicity ratio

[M/H]

Distance

3.37 parsec

Light-years 11.01 ly

V-band magnitude

11.12 mag

Voyager-speed travel 194,095 yr

Multi-band Host Photometry — 9 bands

Astrometric Data

Parallax

296.307 mas

Total Proper Motion

1,365.937 mas/yr

PM Right Ascension

607.68 mas/yr

PM Declination

-1,223.32 mas/yr

Galactic Cartesian (pc)

x = -0.998 · y = 0.053 · z = 0.014

Equatorial (J2000)

RA 176.93760° · Dec 0.79929°

Galactic ℓ, b

270.157° · 59.556°

Ecliptic λ, β

176.868° · -0.484°

HTM-20 index

-1767574165

Observation Record

Photometric series

Stellar spectra

Archive notes

Wikipedia → Image: Wikimedia Commons · ESO/M. Kornmesser · CC BY 4.0