i meander through here (only sometimes with purpose)

Let's say the exterior of Rocky's carapace stays close to 210°C/410°F like his ambient atmosphere/ACS. (Really, I think it'd stay a bit warmer outside of mid-sleep cycle especially around where he 'breathes' due to the 305°C/581°F HCS.) Either way, when Book!Grace touched him it'd be very similar to laying your palm on a pizza stone in a conventional home oven (don't) and for Movie!Rocky to grip him hard enough to drag of course made a deep burn.

Since leaky space blobs are typically 37°C/98.6°F, the temperature difference between skin and carapace is around 173°C/311.4°F. So, when we say Grace is 'icy' in comparison to Eridians, we're just not being nearly dramatic enough. (Ice is only 37°C/66.6°F colder than skin.)

Dry ice (-78.5°C/-109.3°F) gets us closer, with a difference of 115.5°C/207.9°F compared to human flesh, but we're still not quite there. Liquid Nitrogen (−196°C/−321°F) takes us past the skin-to-carapace difference range, with a difference of 233°C/419.6°F. While we're now past the contact difference range, the ambient temperature of the Hail Mary would be lower and closer to this analog.

For Rocky to touch Grace is analogous to a human touching something halfway between dry ice and liquid nitrogen. That's contact frostbite. It's a burn.