Exoplanet · mini-Neptune
K2-138 c
K2-138 c is a mini-Neptune orbiting the star K2-138. Its year lasts 3.56 Earth days. It was discovered in 2017 by the Transit method.
| Host star | K2-138 |
|---|---|
| Distance | 660.8 light-years (202.6 pc) |
| Orbital period | 3.56 days |
| Orbital radius | 0.0446 AU |
| Eccentricity | 0.045 |
| Radius | 2.3 R⊕ · 0.205 R♃ |
| Mass | 6.31 M⊕ · 0.0199 M♃ |
| Density | 2.8 g/cm³ |
| Surface gravity | 1.19 × Earth |
| Equilibrium temperature | 1,012 K (739 °C) |
| Stellar flux received | 279 × Earth |
| Discovery method | Transit |
| Discovery year | 2017 |
| Discovered by | K2 |
Habitable zone
Inside the inner edge of the habitable zone: it receives 279 times the light the Earth does, too hot to keep liquid water on its surface.
Its star in the sky
In the planet's sky its star is a disc 10° across: 19 times the Sun as we see it from Earth.
In the sky
A telescope is needed to see it: its apparent magnitude is 12.25. Visible from the whole Southern Hemisphere and north to latitude 79° N. South of latitude 79° S it never sets. It stands highest at midnight in September, the best time to observe it.
Light's journey
The light you see tonight set out around the year 1365. At the speed of Voyager 1, the fastest craft leaving the Solar System (16.9 km per second), the trip would take 12 million years.
Planets in the same system
Data: NASA Exoplanet Archive, PSCompPars. Its look in the simulation is a rendering based on the measured radius, mass and temperature.