#fotd1273

#1273: ice is really weird. for one, water can exist below 0°C in high pressures, which is fairly unique to liquids. at roughly 0.006 atmospheres and 273.16°K, the triple-point between water, steam and ice means you can have all three coexisting - this is how the Kelvin was formerly defined. but if you thought it was just about the three states of matter - well that'd be boring. there are actually 19 (phase is a better word) of just ice! under various pressures and temperatures, the molecules rearrange into different structures with different properties (and there are some weird proton shenanigans going on too). for example, ice XI is a hydrogen-ordered form of ice I(h) - the latter is the one you're probably familiar with unless you're an experimental physicist. the former actually comes in two varieties - orthorhombic, at low temperatures (found on exomoons) and hexagonal, at 10M atm of pressure. this doesn't even touch the amorphous states! also, ice is predicted to become a metal at 15M atm. as insane as that might sound, it's not the weirdest thing - the most common form of ice in the universe is low-density amorphous ice, which is a liquid, but about as viscous as typical melting glass (think glass-blowing). new ices are being discovered all the time - in 2023, medium-density amorphous ice was discovered.