![K2-3 d: Habitable Zone, 45-Day Year](https://cdn.slatesource.com/a/c/2/ac20a703-10e8-4309-8007-1dd1f0d27a9f.webp) # K2-3 d: Habitable Zone, 45-Day Year - [Made in Slatesource](https://slatesource.com/@steph/k2-3-d-habitable-zone-45-day-year) - By [Steph](https://slatesource.com/@steph) - Created on Sep 19, 2026 ## Super-earth around K2-3 It is 1.46 times Earth's radius, closest in size to Earth, and 2.2 times Earth's mass. A year there lasts 44.56 days, on an orbit 2 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 305 K, in the range where liquid water is possible. The host star K2-3 runs at 3844 K with 0.55 times the Sun's mass. What this planet has and has not got 0% Inside the habitable zone, computed from the star's luminosity. Yes. A measured mass, not just a radius. Yes. A measured temperature rather than one derived from the star. Yes. Any detection of an atmosphere. Not recorded in the archive. journey·3 Planets # K2-3 from the inside out Orbit / Planet "mini-Neptune, 501 K. "super-Earth, 372 K. "super-Earth, 305 K. Radius 1.46 Earth radii Mass 2.2 Earth masses Equilibrium temperature 305 K (measured) One year 44.56 days Orbit radius 0.2014 AU Host star K2-3 at 3844 K Distance 144 light-years Starlight blocked 0.060% at each transit What you get from the shadow The depth of the dip is the ratio of the two discs, so the radius follows. K2-3 has 3 known planets. Planets in company tug on each other, and those tugs are measurable, which is how masses get pinned down without a wobble. Found by K2 in 2015, the second life of the Kepler spacecraft after two of its reaction wheels failed and it could no longer hold a fixed stare. Size from the shadow, mass from elsewhere. Most transiting planets never get the second half, and without it composition stays a guess. # K2-3 d sits in the habitable zone on the arithmetic alone. That says where it \\ orbits, not what it is like. What would you want measured next before calling it promising? No comments yet. Be the first. Log in to comment [NASA Exoplanet Archive: the full record for K2-3 d](https://exoplanetarchive.ipac.caltech.edu/overview/K2-3%20d?utm_source=slatesource)