It turns out that exo-planets come in may varieties and sizes. This we know, now that Kepler has identified more than 5,000 of them — and the JWST is identifying dozens more, every day — almost incidentally.

But an abiding mystery has been… why are there so few rocky “Super Earths” — ones with atmospheres, and about two and a half times the size of our Earth?

Well, a bunch of smart NASA exo-planetary scientists have likely solved the mystery — with a bevy of older Kepler data, thus:

…Some exoplanets seem to be losing their atmospheres and shrinking. In a new study using NASA’s retired Kepler Space Telescope, astronomers find evidence of a possible cause: The cores of these planets are pushing away their atmospheres from the inside out.

Exoplanets (planets outside our solar system) come in a variety of sizes, from small, rocky planets to colossal gas giants. In the middle lie rocky super-Earths and larger sub-Neptunes with puffy atmospheres. But there’s a conspicuous absence – a “size gap” – of planets that fall between 1.5 to 2 times the size of Earth (or in between super-Earths and sub-Neptunes) that scientists have been working to better understand….

[E]xactly how these planets are losing their atmospheres [and shrinking back to near Earth sizes] has remained a mystery. Scientists have settled on two likely mechanisms: One is called core-powered mass loss; and the other, photoevaporation. This study has uncovered new evidence supporting the first….

Now you know… now, a middle school geared NASA explainer:

And… hey there, you “Super Earth”, out now, around the border — (likely on a field trip) — grinning….

नमस्ते