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I have a new paper out! Over the weekend I'll do a thread on what the Solar System can tell us about rocky exoplanets— but for now, enjoy this to-scale set of cross sections I made of the rocky worlds in *this* system! (They're all different, but still all variations on a theme...)

Paul Byrne

@theplanetaryguy.com

Also, note that we have the least information about Venus' interior of any of these bodies, even Io. So that's why it isn't shown with a solid inner core. Maybe it has one! But we can't yet tell.

12/9/26, 2:39 am0 reposts65 likes

Moonlight Breeze

@moonbreeze.bsky.social

12 Sept

Thank you for this note, because I was wondering if new research called into question it having a core like the other rocky worlds. Can't wait for more Venus efforts to help us ascertain its internal composition.

Paul Byrne

@theplanetaryguy.com

12 Sept

Also, note how Mercury is basically a giant iron ball bearing

Zinzrinz

@zinzrinz.bsky.social

12 Sept

Wait, Mercury's inner core is of similar size to that of the Earth's? Does that mean Mercury was roughly Earth-sized in the distant past?

Compton Scatterbrained

@comptonscatter.bsky.social

12 Sept

Don't think it was that big, but it has certainly shrunk from a larger past size! I'm kinda pissed CNN's link to Geophysical Research Ketters 404s though... the hell? lite.cnn.com/2026/09/10/s...

lite.cnn.comMercury: The smallest planet in our solar system is shrinking | CNN

Brian Halligan

@halligan.bsky.social

12 Sept

I wonder how bright Mercury would be in our sky if it were polished like a ball bearing.