Key parameters at a glance
- A radius of 4.79 Earth radii
- A mass of 20.50 Earth masses
- Surface gravity around 0.89 g
- An orbital period of 5.369 days
- Semi-major axis 0.0399 AU
- Distance from Earth 20.54 light-years
- Earth Similarity Index 0.488
- Travel time at Voyager 1 speed 362,252 years
- Almost certainly tidally locked to its host star given the close orbit
Context from the literature
Gliese 581b or Gl 581b is an exoplanet orbiting within the Gliese 581 system, located 20.5 light-years away from Earth in the Libra constellation. It is the first planet discovered of three confirmed in the system so far, and the second in order from the star.
Excerpted from Wikipedia · full article
2 siblings around GJ 581
GJ 581 b shares its host star with 2 other confirmed planets. Side-by-side measurements below.
GJ 581 b Planet Profile
Physical Specs
Classification
Planet Type
Neptune-like
Discovery
Size rank in cohort
Rank by radius
#413of 574
top 71.8%
This planet
4.79R⊕
Neptune-like median
6.39R⊕
Nearest-size peers
| Metric | Earth | GJ 581 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 4.79 | 11.21 |
| Mass (M⊕) | 1.00 | 20.50 | 317.83 |
| Density (g/cm³) | 5.51 | 1.02 | 1.33 |
| Surface Gravity (g) | 1.00 | 0.89 | 2.53 |
| Insolation (S⊕) | 1.00 | — | 0.037 |
Alternative Mass Estimates
| Method | Value | Interpretation |
|---|---|---|
| Best measured mass | 20.500 M⊕ | Direct mass measurement (not derived). |
| Minimum mass (M sin i) | 15.200 M⊕ | Lower bound from radial-velocity fitting. |
Star Catalogue Identifiers
HIP
HIP 74995
TIC
TIC 36853511
Gaia DR2
Gaia DR2 6322070093095493504
Gaia DR3
Gaia DR3 6322070093095493504
System
GJ 581
Percentile among Neptune-like cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 5.37 Earth days (1.5% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0399 AU.
Extended Orbital Architecture
RV semi-amplitude (K)
12.300 m/s
Transit mid-time (BJD)
2,454,724.6310
Long. of periastron (ω)
54.00°
Angular separation (arcsec)
6.34000
Eq. Temperature
—
Insolation (S⊕)
—
Earth = 1.00
Earth Similarity (ESI)
0.488
0 = alien, 1 = Earth-identical
Insufficient insolation data. Close-orbiting tidally-locked around a cool host.
Discovery Paper
Primary reference
Bonfils et al. 2005Instrument
HARPS Spectrograph
Publication
2005-12
Observation locale
Ground
Discovery cohort
Planets confirmed in 2005 at La Silla Observatory (10 shown).
Host System: GJ 581
Spectral Class
M-type red dwarf
Effective Temperature
3,500 K — cooler than the Sun (5,778 K)
Estimated Age
4.30 Gyr — younger than the Sun (4.6 Gyr)
Stellar Radius
0.302 R☉
Stellar Mass
0.295 M☉
Metallicity [Fe/H]
-0.08
Extended Stellar Properties
Surface gravity (log g)
4.970 dex
Stellar density
12.224 g/cm³
Systemic radial velocity
9.75 km/s
Rotational v·sin i
2.00 km/s
Rotation period
132.50 days
Activity index (log R'HK)
-5.480
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 12 bands
Astrometric Data
Parallax
158.749 mas
Total Proper Motion
1,225.326 mas/yr
PM Right Ascension
-1,221.47 mas/yr
PM Declination
-97.13 mas/yr
Galactic Cartesian (pc)
x = -0.639 · y = -0.757 · z = -0.134
Equatorial (J2000)
RA 229.85647° · Dec -7.72269°
Galactic ℓ, b
354.072° · 40.022°
Ecliptic λ, β
229.513° · 10.255°
HTM-20 index
2005289755
Observation Record
Photometric series
3
RV measurements
3
Stellar spectra
5
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