Could evaporating hot Jupiters have metallic hydrogen on their surfaces? Jupiter is believed to have metallic hydrogen in its core. And gas giants that migrate to become hot Jupiters are believed to evaporate, have their atmospheres blown away by their nearby star. Can metallic hydrogen (or some other exotic materia) be detected on the surface of such a planet, or does it require high pressure to exist? What happens to the metallic hydrogen? Does it release much energy if and when it is transformed?
Metallic hydrogen is an odd substance. When you push hydrogen atoms very close together, their electrons can come free, and move around, instead of being tightly bound to the atomic nuclei. As this form of hydrogen would conduct electricity, it behaves like a metal. At least this is the theory. Nobody has been able to produce enough pressure to actually make any metallic hydrogen in the lab.

However, the pressure inside Jupiter should be high enough to form metallic hydrogen. In extrasolar planets there could be large amounts of metallic hydrogen too.

However as soon as you release the pressure from metallic hydrogen, it turns back to normal molecular hydrogen. So it could not exist on the surface of a "hot jupiter", even one from which the outer layers had been stripped away by the solar wind. The metallic hydrogen that had been in the interior would change back into molecular hydrogen as it approached the surface.