tinychaseExoplanet kiosks · planet sizes, transit discoveries
The Radius Valley
Line up every transiting planet by size and a gap appears: there are plenty of worlds around 1.4 times Earth's radius and plenty around 2.4, and strangely few at 1.8. The small ones are rock. The larger ones wear a thick hydrogen atmosphere that doubles their size. In between, a planet's atmosphere tends not to survive its star. Switch the host star to see the gap move.
Size against orbit
The same planets, radius against orbital period. The valley is the sparse diagonal band: closer to the star it sits at larger radii, because a hotter planet loses more of its atmosphere. Hover a dot.
What the gap is
A planet that forms with a rocky core and a few percent of its mass in hydrogen ends up about twice the size of the bare core. Whether it keeps that envelope depends on how much starlight it takes: close in, the atmosphere boils off over the first hundred million years and the planet drops to the rocky peak; farther out, it holds on and sits on the puffy peak. Almost nothing stays in between for long, so the middle empties out.
Around cooler, smaller stars the whole pattern shifts to smaller radii, as the models of atmosphere loss predict. Around the hottest stars in the sample the survey is also less sensitive to small planets, so the low peak thins for a second reason.
The archive lists a radius for three quarters of confirmed planets. This kiosk keeps transit discoveries with a period under 300 days and a radius between half and six Earths, where the measurement is direct and the sample is deep enough for the histogram to mean something.
Data: TerraPulse exoplanet dex (NASA Exoplanet Archive, confirmed planets table; US federal public domain), exported 2026-09-27. Transit discoveries only, orbital period 0.3 to 300 days, radius 0.5 to 6 Earth radii, binned in equal steps of log radius. The valley position is the minimum of a lightly smoothed histogram between 1.45 and 2.25 Earth radii and moves by a bin or two with the smoothing; the physics reading follows Fulton et al. 2017 and the photoevaporation and core-powered mass-loss models that followed. Host-star temperature groups use the archive's effective temperature. Radii carry their own uncertainties, often ten percent or more, which blurs the gap.