It's ice, Jim, but not as we know it!

[Sapyx]

Just happened to explore the Tida system while on my way to Heike for the latest tea CG. I always stop and explore while enroute to anywhere (I'm halfway past Trailblazer rating and I've never left the Bubble yet).

Anyway, Tida's a pretty boring system. Uninhabited. Class G primary star with an M-class partner and a single planet in orbit of the primary - you can scan the whole system in less than a minute, if you can be bothered.

The single planet's an ice giant, 23 earth masses, in an eccentric orbit about 28 Ls out from the star. No atmosphere, no volcanism, surface 72% ice. Nothing more to see here, move along.

Hang on, I say, a planet that close to a star that big and bright can't be ice. What's the surface temperature?

842 degrees Kelvin.

Now, it's got an eccentric orbit - 0.3487 eccentricity, definitely semi-cometary in shape - but it still wouldn't go out far enough to freeze water. Besides, I'm assuming 842 K is the average surface temperature.

The universe really is weirder than I can imagine, because I have no idea what kind of "ice" doesn't melt at temperatures hot enough to melt lead. :S

 

[Danger Mouse]

I seen a few planets like this. I like to think the surface is actually made of crystal like Krypton (1978 version) and the scanner is just getting it confused.

 

[Bobo]

Doesnt water go through some strange changes when under super duper high pressure (scientific/technical term), as in freezes when it shouldnt?

 

[3941]

In Space Engine I saw something recently which was called "Hot Ice Giant". And it was indeed hot, and frozen.
So it's probably a real thing. And I think Bobo might be on to something.

 

[kpmop]

Doesnt water go through some strange changes when under super duper high pressure (scientific/technical term), as in freezes when it shouldnt?

Yeah, simplisticly, increasing pressure balances increasing temperature (and vice-versa). The 23 earth masses could account for the pressure (due to gravity). The 28 ls orbit is approx 8.5 million km (300,000 * 28) which is quite close to the star (mercury is ~58 million km from the sun - though obv different star class), so that could account for the heat...maybe.

(IANAAP!)

 

[iain666]

Doesnt water go through some strange changes when under super duper high pressure (scientific/technical term), as in freezes when it shouldnt?

As pressure goes up the melting and boiling points increase. You can't make a proper cup of tea at the top of a high mountain because the water boils before it gets hot enough, and the sea water around mid ocean ridges is happily liquid at temperatures in the region of 600K.

That's how most volcanoes work too - rock is moved up from depth and melts as it gets near the surface not because the temperature is increased but because the pressure is decreased and it crosses the melting line without getting hotter (adiabatic melting if you want the technical term).

Apply sufficient pressure and you can get really hot ice - but don't worry about the lead, it would be resolutely solid at those temperatures with the same pressure.

Everything works like that - water does have some weird properties but the melting "point" actually being a line when you look at both temperature and pressure is one that everything shares.

 

[ThoroughlyLostExplorer]

Hi, I somehow still think there is something wrong with the planet because pressure effects on the water/ice happen inside and not on the surface. At this kind of temperature, I'd expect a 100% water atmosphere of considerable size made by steam and possibly a liquid layer on top of the solid core. While any liquid layer would arguably included in the basic planet description (it's not going to be a water world "with life" at these temperatures), the atmosphere would have to show up on our display. I guess think this whole construct might better be rated "water giant".

I'm not too sure about the liquid layer though, because at the temperature / pressure point I'd expect it to form there will possibly something else happening, e.g. sublimation (direct solid <-> gas transition), or a more exotic state of water. And that leads me right to:

Water is actually an extremely weird material when it comes to melting points. The reason is that ice has a hexagonal crystalline structure that takes up more space than very cold liquid water, causing ice to float. While very high pressure can keep it solid under strange conditions, more modest amounts of pressure will actually make ice go liquid as the crystalline grid is forced together into a smaller volume. This is how glaciers and, uh, ice skates work.

I'm rather certain that the solid state of water under high pressures won't be "ice" proper but a solid form of different structue, e.g. amorphous without crystalline structure. This kind of thing will likely exhibit some properties of a solid and some of a liquid so it would be given an own name with a description saying we can't properly tell if it is liquid or solid.

Ok guys, you have made me curious again about water I'll have to read up on the details one of these days.

 

[iain666]

At 72% ice composition the metal content is probably tiny so there's not going to be any magnetic field to shield it from the stellar wind so any vapour subliming at the surface might be getting lost in space as fast as it appears leading to the lack of atmosphere.

 

[Frank]

There is a technical explanation why water behaves the way it does under certain temperatures and pressures... it's weird!