![KOI-55 c: A Year In 8.2 Hours](https://cdn.slatesource.com/1/6/3/16316c9a-7385-4448-8d62-02096f2affe8.webp)

# KOI-55 c: A Year In 8.2 Hours

- [Made in Slatesource](https://slatesource.com/@steph/koi-55-c-a-year-in-8-2-hours)
- By [Steph](https://slatesource.com/@steph)
- Created on Sep 19, 2026

## Terrestrial around KOI-55

It is 0.87 times Earth's radius, closest in size to Venus, and 0.7 times Earth's mass. A year there lasts 8.2 hours, on an orbit 51 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 6321 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.

**6321** K: hot enough to vaporise rock on the dayside

Radius

0.87 Earth radii

Mass

0.7 Earth masses

Equilibrium temperature

6321 K (derived)

One year

8.2 hours

Orbit radius

0.0076 AU

Host star

KOI-55 at 27730 K

Distance

4015 light-years

The state of the record for this planet

0%

A measured radius. Yes.

A weight, not just a width. Yes.

A density, which decides rock or gas. No.

A semi-major axis. Yes.

A measured temperature rather than a derived one. No.

An eccentricity, so we know if the orbit is a circle. No.

The archive lists no measured equilibrium temperature for this planet. The 6321 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?

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[NASA Exoplanet Archive: source data, including the values not used here](https://exoplanetarchive.ipac.caltech.edu/overview/KOI-55%20c?utm_source=slatesource)