Key parameters at a glance

A radius of 2.02 Earth radii
A mass of 3.63 Earth masses
Surface gravity around 0.89 g
An orbital period of 6.268 days
Semi-major axis 0.0684 AU
Equilibrium temperature 1,170 K (897 °C)
Distance from Earth 59.59 light-years
Earth Similarity Index 0.226
Travel time at Voyager 1 speed 1,050,858 years

2 siblings around HD 39091

pi Men 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
pi Men c this	Sub-Neptune	2.02	3.63	6.268	1,170	2018
pi Men d	Sub-Neptune	3.72	13.38	124.640	—	2022
HD 39091 b	Gas Giant	12.30	4,481.38	2,088.800	—	2001

pi Men c Planet Profile

Physical Specs

Radius

2.02 R⊕

Radius (Jupiter)

0.180 R♃

Mass

3.63 M⊕

Mass (Jupiter)

0.011 M♃

Density

2.80 g/cm³

Surface Gravity

0.89 g (Earth)

Classification

Planet Type

Sub-Neptune

ESI Score 0.226

HZ Position Inner

Controversial No

Discovery

Year 2018

Method Transit

Facility Transiting Exoplanet Survey Satellite (TESS)

Telescope 0.1 m TESS Telescope

Size rank in cohort

Rank by radius

#1937of 1978

top 97.9%

This planet

2.02R⊕

Sub-Neptune median

2.71R⊕

Nearest-size peers

TOI-544 b 2.02 R⊕ Kepler-833 b 2.02 R⊕ Kepler-343 c 2.02 R⊕

Metric	Earth	pi Men c	Jupiter
Radius (R⊕)	1.00	2.02	11.21
Mass (M⊕)	1.00	3.63	317.83
Density (g/cm³)	5.51	2.80	1.33
Surface Gravity (g)	1.00	0.89	2.53
Insolation (S⊕)	1.00	309.00	0.037

Alternative Mass Estimates

Method	Value	Interpretation
Best measured mass	3.630 M⊕	Direct mass measurement (not derived).
Minimum mass (M sin i)	3.496 M⊕	Lower bound from radial-velocity fitting.

Star Catalogue Identifiers

HD 39091

HIP

HIP 26394

TIC

TIC 261136679

Gaia DR2

Gaia DR2 4623036865373793408

Gaia DR3

Gaia DR3 4623036865373793408

System

HD 39091

Percentile among Sub-Neptune cohort

Radius 2.019 R⊕ · percentile 2 / cohort 1978

Mass 3.630 M⊕ · percentile 1 / cohort 1978

Orbital period 6.27 d · percentile 19 / cohort 1946

Distance 18.27 pc · percentile 4 / cohort 1975

ESI 0.226 · percentile 11 / cohort 1978

Orbit & Habitability

Orbital Dynamics

Period

6.268 days

Semi-major axis

0.0684 AU

Eccentricity

0.000

Inclination

87.05 °

Year Length

A year here lasts approximately 6.27 Earth days (1.7% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0684 AU.

Transit Fingerprint

Depth

0.027 %

Duration

2.952 h

Impact parameter b

0.647

Rp / R★

0.015844

Transit midpoint (BJD)

2,458,425.7892

Photometric dip

Transit produces a flux drop of 268 ppm lasting ≈ 2.95 h.

Extended Orbital Architecture

Planet / star radius ratio

0.015844

Semi-major axis / stellar radius

13.100

Impact parameter (b)

0.647

RV semi-amplitude (K)

1.185 m/s

Transit mid-time (BJD)

2,458,425.7892

Long. of periastron (ω)

0.00°

Sky-projected obliquity (λ)

-24.00°

True obliquity (ψ)

26.90°

Angular separation (arcsec)

3.74000

Eq. Temperature

1,170K

(897 °C)

Insolation (S⊕)

309.00

Earth = 1.00

Earth Similarity (ESI)

0.226

0 = alien, 1 = Earth-identical

Inside the inner HZ boundary (too hot for liquid water) — the dayside is scorched.

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

Gandolfi et al. 2018

Instrument

TESS CCD Array

Publication

2018-11

Observation locale

Space

Discovery cohort

Planets confirmed in 2018 at Transiting Exoplanet Survey Satellite (TESS) (2 shown).

HD 219666 b · Neptune-like HD 1397 b · Gas Giant

Host System: HD 39091

Spectral Class

G-type yellow (Sun-like)

Effective Temperature

5,998 K — hotter than the Sun (5,778 K)

Estimated Age

2.98 Gyr — younger than the Sun (4.6 Gyr)

Stellar Radius

1.170 R☉

Stellar Mass

1.070 M☉

Metallicity [Fe/H]

0.09

Extended Stellar Properties

Surface gravity (log g)

4.430 dex

Stellar density

0.945 g/cm³

Systemic radial velocity

10.71 km/s

Rotational v·sin i

3.16 km/s

Rotation period

18.30 days

Activity index (log R'HK)

-4.970

Metallicity ratio

[Fe/H]

Distance

18.27 parsec

Light-years 59.59 ly

V-band magnitude

5.65 mag

Voyager-speed travel 1,050,858 yr

Multi-band Host Photometry — 11 bands

Astrometric Data

Parallax

54.705 mas

Total Proper Motion

1,094.030 mas/yr

PM Right Ascension

311.19 mas/yr

PM Declination

1,048.84 mas/yr

Galactic Cartesian (pc)

x = 0.016 · y = 0.165 · z = -0.986

Equatorial (J2000)

RA 84.29928° · Dec -80.46460°

Galactic ℓ, b

292.508° · -29.776°

Ecliptic λ, β

273.901° · -76.019°

HTM-20 index

1068394155

Observation Record

Photometric series

RV measurements

Stellar spectra

Archive notes