On Pluto, mountains means water.
If you’ve stayed with us through this article, you know how important it was to discover an 11,000-foot mountain range of mountains on Pluto, with only one substance being hard enough to build them in Pluto’s environment: water. Here is another look at those mountains, as well as the Sputnik Planum (of methane ice):
Here’s the Science so far on Pluto’s Icy Mountains and Bumpy Plains
The first thing that jumps out is an absence of craters, even with more of the Sputnik Planum to scour. Based on normal cratering rates, that dates the plains to being recently surfaced within the last 100 million years. For context, that’s younger than Appalachian Mountains. To be craterless, Pluto has to-be-determined active geologic processes resurfacing the world in the recent past. This is hugely unexpected. (Really: it left me flailing).
A geologically active Pluto breaks our theories of activity on icy worlds. We thought the only way to get that kind of geological activity was tidal massage from a friendly neighbourhood gas giant. The closest Pluto has is Charon, its largest moon. Charon lacks the gravitational influence to jerk around Pluto’s interior enough to spur activity both because of its small size and because it is tidally locked. Being tidally locked means the two worlds always face each other as they dance around their mutual center of mass, minimizing tidal stresses.
That leaves rethinking how thermodynamics apply at the dwarf planet. Pluto should be too cold to be active, but it isn’t. The best options for revising our theories are that its initial heat source lasted longer than anticipated through a yet-to-be-described process, that heat was stored, or that the heat is used more efficiently.
If Pluto is made of the normal mix of silicate minerals for a rocky world in our solar system, then we’d expect that it’s radioactive elements have decayed enough to no longer be a significant heating source. It’s likely that Pluto and Charon collided in the past, the stability, circularity, and tidal equilibrium of their orbits indicate any collisions were a long time ago, so that isn’t a recent heat source either. But, there could be a loophole: the heat of impact could have created a subsurface ocean. Once a subsurface ocean forms on an icy world, it’s likely to stick around a long time due to a convenient feedback loop. Freezing increases the concentration of ammonia, a natural antifreeze that inhibits further freezing. A subsurface ocean could store a lot of heat, possibly even driving icy plate tectonics. This idea was predicted by astrophysicists Amy Barr Mlinar and Geoffrey Collins, who are hoping we find any evidence of ancient tectonic features on Pluto or Charon to support their theory of an impact-generated subsurface ocean.
A Carbon Monoxide Bulge in Tombaugh Regio
In the first map of frozen carbon monoxide concentration shows one very distinctive bulge in the Tombaugh Regio. This matches up with the red half splitting the heart of Pluto from the enhanced color image released last week. The concentrations increase towards the center of the contoured bull’s eye.
The Ralph image detected a bulge of carbon monoxide in the western lobe of Tombaugh Regio. Image credit: NASA/JHUAPL/SwRI
We don’t know what this concentration means yet, nor why it’s happening only in Tombaugh Regio and no where else, but it is deeply suspicious that it’s also in a region that seems to be actively resurfacing.
The Icy Peaks of Norgay Montes
Along the boundary between the light heart of Pluto and the darker whale — now known as the Tombaugh Regio and Cthulhu Regio respectively — is a respectable mountain range. Norgay Montes are named for Tenzing Norgay, the sherpa who summited Mount Everest with Edmund Hillary in 1953.
The spiked peaks jut up to 3,300 meters (11,000 feet) above the oddly-craterless plains. For context, those are mountains that are on par with the Rockies here on Earth, no rescaling necessary.
This is the first exposed bedrock (or more accurately, “bed ice”) of Pluto. We haven’t definitively nailed down its composition yet, but to hold such rugged topography, it needs to be hard. The current best-guess is water ice, which at Putonian temperatures is far harder than the methane and nitrogen ice.
(For this article, we’ll skip “The Bumpy Plains of Sputnik Planum,” but please see the source article here for that discussion.)
Except: Elsewhere [on the Sputnik Planum], long dark streaks stretch several kilometers (a few miles), all apparently aligned in the same direction off of larger dark regions. These may be windblown traces, produced as wind scours the surface of the icy plains. They could also be geysers, the sought-after evidence of cryovolcanism.
