Pluto's mountains are also snow-covered, but not for the same reasons as on Earth
Pluto's mountains are also snow-covered, but not for the same reasons as on Earth
In 2015, the New Horizons spacecraft brought back a series of images of the planet Pluto, including one showing the snow-capped peaks of mountains that are not far from reminding us of our Alps. A mystery…
On the left, the region of "Cthulhu" of Pluto and on the right, the Alps on Earth. The two landscapes are very similar. In both cases, mountain ranges with ice-covered peaks.
The images of the dwarf planet brought back in 2015 by the New Horizons spacecraft have not finished surprising us. It was from these that scientists developed the theory of the existence of a liquid ocean beneath pluto's frozen surface. The Images from New Horizons also show a wide variety of landscapes on the surface of the dwarf planet, sometimes with a disturbing resemblance to what can be found on Earth.
Methane ice
This is the case for these snow-capped peaks in the Cthulhu region, which a team of CNRS scientists led by astrophysicist François Forgettried to unravel the mystery in a study published on Tuesday in Nature Communications. "We knew it couldn't be water ice like on Earth," says Forget. It takes far too cold on Pluto - in the order of -230oC on the surface - for the water to condense and be present as steam in the atmosphere.
Pluto's atmosphere is composed mainly ofnitrogen as well as some trace gases that can condense. "Like methane,"says François Forget. It is a bit like water on Earth, being that gas that can condense to form clouds, snow, ice...
Snow, not for the same reasons as on Earth
In other words, the snows observed at the mountain peaks of the Cthulhu region are methane snows. But once that said, we only went halfway. It remains to be understood how this ice got there. "You would have thought the process was similar to what's happening on Earth," says the astrophysicist. When the air rises to altitude, it cools and condenses [water vapour, it returns to the liquid state in the form of clouds, fog, mist, frost...]. But on Pluto the phenomenon is the opposite. Temperatures warm with altitude.
François Forget makes the parallel with the stratosphere, the second layer of the Earth's atmosphere. "Get on a plane at an altitude of 10,000 metres, you'll see it's very cold, in the order of minus 50 degrees Celsius," he begins. But if you go into the stratosphere, as some planes allow, you will find that it is suddenly very hot again, because ozone absorbs solar radiation.
On Pluto, methane plays this role. And by capturing the solar radiation, it causes significant temperature differences between the surface (at 230 degrees Celsius) and "the atmosphere, much warmer, up to -170 degrees," says François Forget. However, as they rise in the atmosphere, these mountains, with their always very cold surface, will rise on contact with this warmer, methane-laden air. And that's who's going to allow that gas to condense. And thus form this layer of ice at the tops of these mountains.
A layer of frost that accumulates
It remains to be seen what consistency this methane ice is. Could we take a handshake like our water ice on Earth? Not easy to respond from the images of New Horizons. "Based on the Pluto climate simulation models we used, we think more that this methane ice condenses directly to the surface of these mountains," says Forget. In other words, there would be no snowfall, but rather a very thick form of frost that accumulates over years. This layer is thick enough that the surface cannot be seen below. On the other hand, it is very difficult to determine its exact thickness. Probably in the order of a few centimetres.
These snow-capped peaks in the Cthulhu region are just a small part of the world to discover that constitutes Pluto. Much further east of the Cthulhu region, this results in very thick methane glaciers, the astrophysicist says. And at another place still a large cap on nitrogen fleece. "Our goal is to have a kind of simulator of the planet, based on universal physical equations, in the same way that there is a similar model for the Earth and which allows in particular to study climate change," says François Forget. With the idea behind understanding how Pluto's landscapes were formed in a completely different context from the one we know on Earth.
Source:- Flash News and News Agencies