Key parameters at a glance
- A radius of 2.32 Earth radii
- A mass of 5.99 Earth masses
- Surface gravity around 1.11 g
- An orbital period of 2.260 days
- Semi-major axis 0.0214 AU
- Equilibrium temperature 568 K (295 °C)
- Distance from Earth 205.47 light-years
- Earth Similarity Index 0.455
- Travel time at Voyager 1 speed 3,623,431 years
- Almost certainly tidally locked to its host star given the close orbit
Context from the literature
K2-28 is a metal rich M4-type main sequence star. One confirmed transiting exoplanet is known to orbit this star. There is another star 5.2 arcseconds to the north–east of K2-28. However, this star has a different proper motion, and is therefore physically unrelated and probably a background star.
Excerpted from Wikipedia · full article
K2-28 b Planet Profile
Physical Specs
Classification
Planet Type
Sub-Neptune
Discovery
Size rank in cohort
Rank by radius
#1469of 1978
top 74.2%
This planet
2.32R⊕
Sub-Neptune median
2.71R⊕
Nearest-size peers
| Metric | Earth | K2-28 b | Jupiter |
|---|---|---|---|
| Radius (R⊕) | 1.00 | 2.32 | 11.21 |
| Mass (M⊕) | 1.00 | 5.99 | 317.83 |
| Density (g/cm³) | 5.51 | 2.64 | 1.33 |
| Surface Gravity (g) | 1.00 | 1.11 | 2.53 |
| Insolation (S⊕) | 1.00 | 30.10 | 0.037 |
Star Catalogue Identifiers
TIC
TIC 39926974
Gaia DR2
Gaia DR2 2622296783699476864
Gaia DR3
Gaia DR3 2622296783699476864
System
K2-28
Percentile among Sub-Neptune cohort
Orbit & Habitability
Orbital Dynamics
Year Length
A year here lasts approximately 2.26 Earth days (0.6% of a terrestrial year) on a nearly circular orbit at a mean orbital distance of 0.0214 AU.
Transit Fingerprint
Depth
0.675 %
Duration
0.982 h
Impact parameter b
0.360
Rp / R★
0.073700
Transit midpoint (BJD)
2,456,977.9901
Photometric dip
Transit produces a flux drop of 6,750 ppm lasting ≈ 0.98 h.
Extended Orbital Architecture
Planet / star radius ratio
0.073700
Semi-major axis / stellar radius
17.900
Impact parameter (b)
0.360
Transit mid-time (BJD)
2,456,977.9901
Long. of periastron (ω)
0.00°
Angular separation (arcsec)
0.34000
Eq. Temperature
568K
(295 °C)
Insolation (S⊕)
30.10
Earth = 1.00
Earth Similarity (ESI)
0.455
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
Hirano et al. 2016Instrument
Kepler CCD Array
Publication
2016-03
Observation locale
Space
Discovery cohort
Planets confirmed in 2016 at K2 (12 shown).
Host System: K2-28
Spectral Class
M-type red dwarf
Effective Temperature
3,214 K — cooler than the Sun (5,778 K)
Estimated Age
—
Stellar Radius
0.288 R☉
Stellar Mass
0.257 M☉
Metallicity [Fe/H]
0.26
Extended Stellar Properties
Surface gravity (log g)
4.930 dex
Stellar density
15.200 g/cm³
Metallicity ratio
[Fe/H]
Multi-band Host Photometry — 17 bands
Astrometric Data
Parallax
15.846 mas
Total Proper Motion
320.467 mas/yr
PM Right Ascension
-254.66 mas/yr
PM Declination
-194.55 mas/yr
Galactic Cartesian (pc)
x = 0.902 · y = -0.409 · z = -0.138
Equatorial (J2000)
RA 335.62331° · Dec -7.95635°
Galactic ℓ, b
54.455° · -49.894°
Ecliptic λ, β
334.506° · 2.040°
HTM-20 index
1874278209
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