Interesting. You'd think that a custom radiation-hardened x86 or ARM variant would be sufficient.

Are there any space exploration vehicles running Linux?

ARM is pretty new as a remotely high-performance thing. x86 is used a bit; the Hubble space telescope has a radiation hardened 486, for instance (originally a 386). A good few spacecraft use radiation hardened PowerPCs, M68Ks, and other common designs. Even that ESA chip isn't anything hugely custom; it's a SPARC-V8 variant.

Don't know about exploration, but SpaceX runs Linux for all it's rocket firmware and I imagine Dragon capsules will as well.

There was as discussion with John Muratore (SpaceX director of vehicle certification) posted on HN a while back with some interesting notes on this:

https://news.ycombinator.com/item?id=6125834

Absolutely! Hell, the ISS is all Linux now.

ISS laptops run linux, the ISS control software itself does not run on linux.