Tiny Pluto Big On Frozen Water Reserves

New submitter rmdingler writes that a new map created by NASA based on the New Horizons flyby of Pluto "shows much more frozen water than scientists initially expected." Using LEISA to photograph from 108,000 kilometers away, much more of the recently demoted planet's frozen surface liquid is water, rather than methane, carbon monoxide, and nitrogen as originally posited.

Comments

Re:Amazing that it is not buried

[Rei]

The summary is lousy. It's not "much less water ice than thought", it's much less "than was previously known". It had been hard to detect the water ice through the frosts previously.

It's always been expected that a large portion of Pluto's mass is water ice. Also, it was well known before NH arrived that any surface topography of significance would have to be from water ice, as the other ices are just too "soft" to hold up strong contours.

As for water ice being buried, why would you expect that? Water ice is lighter than nitrogen and carbon monoxide ices. It basically "floats" on them. There seems to be a sort of N2/CO/CH4 "mantle" which is exposed to the surface (and convecting) at Sputnik (the point nearest Charon). Elsewhere, however, a water ice crust floats atop it, seemingly progressively thicker the further one gets from Sputnik/Charon.

I find it interesting - perhaps coincidental, perhaps not - that Pluto is like our moon, with a crust thinner and more geologically active on the side of which it's tidally locked to its partner, and thicker/less active on the opposite side. If we can figure out Pluto's dynamics better, it might help us understand our own moon better.

Pluto is a beautifully, fascinatingly weird place. There's some good evidence that entire water-ice floating mountains have washed ashore and collected on the shores of Sputnik - perhaps water ice from the deep depths. Certainly there are shorelines that have this appearance today, and we can see smaller water-ice chunks floating and stuck between the roiling convection cells. If one pictures rolling back the clock, Pluto started out very hot (alternatively with multiple periods of heat, such as during the formation and/or capture of Charon). The first things to condense out would have been rocks, such as silicates, with a water ice ocean and a nitrogen/methane/CO atmosphere. Then the water ice would have frozen. Then the gases would have frozen atop it. But then you have a situation where you have an extensive heavier layer over an even more extensive, lighter layer. So there may be potential for cycling. But it's hard to say, because different crystal forms in different temperature and pressure conditions have different densities.

Charon also has a look of large chunks of water ice drifting around. But while Pluto has its active mantle exposed to space, Charon seems frozen in time. You can see structures that look like massive islands (or even continents) that have broken off from each other, drifted, then became frozen into place. And there's some crazy-massive rifting, as if some layers changed dramatically in size relative to others as they froze (Pluto too has rifting, but Charon's rifts are even more spectacular)

Re:Water

[Rei]

The summary is wrong. There is no surprise about how much water ice Pluto has, it's always been expected that it's predominantly water ice.

The actual article linked says that the maps show more water ice than was previously known, not than previously thought. It's hard to see through the surface frosts to see the water ice. Mountains are impossible on Pluto without water ice (or other high compressive strength material - aka, not N2, CH4, CO, etc). The instant mountains were seen, we knew that the crust was mostly water ice. And even before then, we knew that - regardless of what its crust was made of - that Pluto is in large part water ice, due to its density (1,86g/cm3).