![KOI-55 b: A Year In 5.8 Hours](https://cdn.slatesource.com/8/5/8/858662a1-baf7-4843-acc7-9a8cb3425df3.webp) # KOI-55 b: A Year In 5.8 Hours - [Made in Slatesource](https://slatesource.com/@steph/koi-55-b-a-year-in-5-8-hours) - By [Steph](https://slatesource.com/@steph) - Created on Sep 19, 2026 ## Terrestrial around KOI-55 It is 0.76 times Earth's radius, closest in size to Venus, and 0.4 times Earth's mass. A year there lasts 5.8 hours, on an orbit 65 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 7114 K (derived from the star rather than measured), hotter than the surface of many stars. The host star KOI-55 runs at 27730 K with 0.50 times the Sun's mass. **7114** K: hot enough to vaporise rock on the dayside Radius 0.76 Earth radii Mass 0.4 Earth masses Equilibrium temperature 7114 K (derived) One year 5.8 hours Orbit radius 0.0060 AU Host star KOI-55 at 27730 K Distance 4015 light-years The state of the record for this planet 0% A size. Yes. A weight, not just a width. Yes. A density, so rock and gas can be told apart. No. An orbital distance. Yes. A measured temperature rather than a derived one. No. An eccentricity, so the orbit shape is known. No. The archive lists no measured equilibrium temperature for this planet. The 7114 K quoted here is derived from the star's output and the orbital distance, assuming a third of the light is reflected. It is an estimate from two numbers, not an observation. KOI-55 has 2 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 Kepler in 2011. Kepler stared at one patch of sky for four years, which is why so many of its planets have short periods: a planet only counts once you have seen it cross several times. # Half the temperatures quoted for exoplanets are calculated from the star, not \\ measured at the planet. Should a page like this show them at all, or leave the field blank? No comments yet. Be the first. Log in to comment [NASA Exoplanet Archive: the full record for KOI-55 b](https://exoplanetarchive.ipac.caltech.edu/overview/KOI-55%20b?utm_source=slatesource)