The
Solar System might be a soggier place than we previously thought - even in the
glacially cold reaches of the Kuiper Belt. There, dwarf planet Pluto could be
harbouring liquid oceans under a shell of nitrogen ice.
It
was thought that the temperature required to maintain a liquid ocean on Pluto
was too high for the thick ice to remain unmelted, but Japanese astronomers
have found a new possibility: A layer of gas under the ice and above the
liquid, insulating the two from each other, and allowing them to coexist.
This
could help solve the gravity
anomaly detected by the New Horizons probe in the form of the Sputnik
Planitia, with its equatorial location and low topography, suggesting a liquid ocean underneath.
A
liquid ocean underneath Sputnik Planitia could also explain tectonic features
on the planet. And yet, based on Pluto's age and location, scientists expected
that all liquid should have frozen solid.
"To
maintain an ocean, Pluto needs to retain heat inside. On the other hand, to
maintain large variations in its thickness, Pluto's ice shell needs to be
cold," the
researchers wrote in their paper.
"Here
we show ... that the presence of a thin layer of clathrate hydrates (gas
hydrates) at the base of the ice shell can explain both the long-term survival
of the ocean and the maintenance of shell thickness contrasts."
The
team hypothesised that a gas
hydrate layer - a solid, ice-like form of water with gas trapped in a
lattice made of its molecules, also called a clathrate - was
responsible. But obviously we can't just nip over to Pluto to check things out,
so they relied on computer simulations.
Starting
4.6 billion years ago, the age of the Solar System, the researchers simulated
the evolution of Pluto, both with and without a gas hydrate layer between the
icy shell that covers the Planitia, and the ocean beneath.
Learn
more here.