One of my favorite things to cover on this channel is our solar system’s multitude
of ice shell moons where ice covers liquid water oceans, some of which could be habitable.
Most interesting to me though is the sheer number we have, the outer solar system is
full of liquid water, which means we have quite a few chances of finding alien biospheres
in our own solar system, even out in the Oort cloud.
The best close chance though is Europa, and those chances have recently gotten better.
It’s always been noted that Europa looks like it has the equivalent of plate tectonics
where you see areas that look similar to Earth’s mid ocean rifts, which implied huge plates
of ice subducting and interacting with the ocean below, similar to how it happens here
with the mantle.
The problem is that on earth density and temperature drive subduction, but that’s in rock.
On Europa, it’s ice and should behave differently so it wasn’t clear just how this subduction
was occurring.
In a new paper by Brandon Johnson and colleagues, links below, they model how it happens and
essentially it comes down to varying amounts of salt in the ice that alters the density
equation and allows subduction to occur.
This bodes well for life, since if you have interaction between a moon’s surface and
the ocean below, surface nutrients can be delivered down deep that would favor life.
This also has broader potential consequences in astrobiology, since one of the things that
supports life on this world is plate tectonics and that may also end up being true for ice
shell worlds, but for different reasons.
We shall see as we have likely have both types of ice shell moon in this solar system, ones
with subduction like Europa, and ones without.
But these are moons, and while we have no known example of this in our solar system,
it’s possible that there could be entire habitable ice shell planets in the universe
and we may have already found one, or one that may have once been an ice shell planet.
This is an old and now obscure discovery, and potentially a rather sad one.
It’s amazing that we even know about this planet since it is very distant, about 20,000
light years out.
Unlike most exoplanets, which are typically discovered either through the gravitational
effects they have on their star, or through drops in light as they pass in front of their
host star, this planet was discovered entirely accidentally during a gravitational microlensing
observation.
This planet has a truly mind-boggling designation, OGLE-2005-BLG-390lb.
We’ll call it what the media called it at the time, Hoth, after the icy world of Star
Wars fame.
It was given that name because it’s thought to be a super earth, thought there is uncertainty
about that.
If it is a super-earth, it is ridiculously cold and orbits far outside the habitable
zone of its star, which is most likely a cool red dwarf.
The story came and went and the media soon lost interest in this ice world that superficially
might resemble a Star Wars planet, though I have to say, it actually doesn’t.
Star Wars Hoth was parka weather, which is almost steamy compared to the surface temperatures
of this exoplanet.
But more came out about this world later that made it far more interesting.
In a paper by David Ehrenreich and colleagues, link below, they explore the idea that if
Hoth were earthlike and had sufficient amounts of water, radioactive decay in the planet’s
core might have once allowed for subsurface oceans for a very long time.
Trouble is, this planetary system is extremely old, about 10 billion years, and it’s thought
that it would not have been able to maintain enough heat to keep that ocean indefinitely
and is likely now frozen solid.
Any life that might have arisen there long ago would also now be frozen solid having
met a slow Armageddon of increasing cold.
One wonders how evolution would deal with that scenario and what might have played out.
Long ago and far, far away indeed.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently pondering the idea
of Europan exoseafood.
The first human colony on Europa could be equipped with a deep fryer.
I don’t know how I’m supposed to feel about that, and be sure to check out my books
at your favorite online book retailer and subscribe to my channel for regular, in-depth
explorations into the interesting, weird and unknown aspects of this amazing universe in
which we live.