![Kepler-51 d: Less Dense Than Cork](https://cdn.slatesource.com/6/f/9/6f966607-3bce-49d8-8693-511987ac9cd7.webp) # Kepler-51 d: Less Dense Than Cork - [Made in Slatesource](https://slatesource.com/@steph/kepler-51-d-less-dense-than-cork) - By [Steph](https://slatesource.com/@steph) - Created on Sep 19, 2026 ## Ice giant around Kepler-51 It is 0.87 times Jupiter's radius, closest in size to Saturn, and 7.6 times Earth's mass, at 0.05 g/cm3, less dense than Earth. A year there lasts 130.19 days, on an orbit 1.3 times Mercury's distance from the Sun. Its equilibrium temperature is 381 K, hotter than any desert. The host star Kepler-51 runs at 6018 K with 1.04 times the Sun's mass. journey·3 Planets # Kepler-51 from the inside out Orbit / Planet "ice giant, 543 K. "ice giant, 439 K. "ice giant, 381 K. Radius 9.70 Earth radii Mass 7.6 Earth masses Equilibrium temperature 381 K (measured) One year 130.19 days Orbit radius 0.5090 AU Host star Kepler-51 at 6018 K Distance 2557 light-years Starlight blocked 0.893% at each transit **0.05** g/cm3: less dense than cork 🔭🪐📅01.01.2012 – 01.01.2014 01.01.2012Kepler-51 b, Kepler-51 c 01.01.2012 01.01.2014Kepler-51 d 01.01.2014 Where this planet stands on each testable criterion 0% Inside the habitable zone. No. Dense enough to be rock rather than gas, at 0.05 g/cm3. No. 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. What a crossing measures The fraction of starlight blocked sets the radius against the star's. Found by Kepler in 2014. Kepler's method needed repetition, not brightness. It could find small planets around faint stars, provided they came round quickly enough to be seen twice. Kepler-51 has 4 known planets. Systems like this are the ones where architecture can be studied instead of guessed at. The size came from a crossing, the mass did not. That pairing is uncommon and it is what lets anyone say whether this is rock or gas. [NASA Exoplanet Archive: every published measurement of this planet](https://exoplanetarchive.ipac.caltech.edu/overview/Kepler-51%20d?utm_source=slatesource)