It's a bird, it's a plane, it's a super... earth.
Perhaps one of the most revolutionary discoveries in modern astronomy is the discovery of an
entirely unpredicted class of planets known as 'super earths'.
These rocky planets mass from anywhere between 2 to 10 times Earth's own mass, are believed
to have a rocky core, and some might even be better suited for life than our own planet.
It was initially believed that the most common type of planet in the solar system were gas
giants- it was a gas giant after all that was the first exoplanet ever discovered by
mankind.
However, as our ability to spot planets in other solar systems increased, scientists
made a shocking discovery- it wasn't gas giants or even small rocky planets like Mercury that
were the most common, but rather large, rocky planets, though as smaller planets are more
difficult to discover our findings may still be accidentally biased.
So why did scientists go with the term Super Earth?
The name comes from the fact that along with a rocky core, these planets are able to retain
a significant atmosphere- features found in only two planets in our own solar system,
Earth and Venus.
However, the name can be misleading, and many have fundamentally misunderstood the nature
of a super earth.
When you think of a super earth after all, you're probably thinking of a planet that's
largely like our own earth, rocky with oceans and a welcoming atmosphere- but that's not
what super earths are at all.
Or at least, that’s not what most super earths are like.
55 Cancri e for example, is a super earth completely covered by an ocean of lava hot
enough to melt iron, basically making it the Mount Doom of planets.
Meanwhile, Gliese 1214 b is believed to be the polar opposite, a water world completely
covered by an ocean.
Within these two extremes, scientists have found a plethora of worlds.
Initially scientists believed that super earths could be super-habitable, and have even better
conditions for life than our own planet.
Their increased size would offer more surface area for life, and be less perturbed by the
gravity of nearby objects and thus offer more climate stability to its inhabitants.
On our own planet the leading cause of extinction is climate change, with periodic ice ages
wiping out vast numbers of species.
At the time, it seemed like the name super earth was quite apt, as these worlds would
be far more habitable than earth.
However, as scientists refined their knowledge of the physics and geological processes on
these super earths through experimentation, a different story began to emerge.
Firstly, the sheer mass of these planets means that many of them are bound to be water worlds.
The increased gravity would attract greater amounts of icy comets than our own smaller
earth did, leading to planet-spanning oceans that could be miles deep.
And what's wrong with that, you might ask, after all life almost certainly began in the
ocean on our own planet, and the ocean remains far more biodiverse than land does.
More water should mean more life, right?
Well, the biggest problem with a large water world is that the increased gravity and great
depth of its oceans would smash water molecules together into ice formed not by low temperatures
but incredible pressure.
This extremely dense layer of ice would act as a form of sealant around the rocky core
of the planet, blocking off the core from the surface and shutting off the carbon cycle
for the world.
This may be biased towards carbon-based life forms, but even if non-carbon based lifeforms
are possible, this thick ice layer would shut off vital minerals regularly exposed by geological
processes on smaller worlds, and prevent them from entering the biological life cycle.
Even if you aren't covered in water, that big gravity field is going to be a problem
for the exact same reason- a super earth is going to attract a lot more celestial objects,
and thus be prone to much more extinction level events from asteroid impacts.
While that wouldn't preclude life entirely, cyclical extinction level impacts certainly
would make the evolution of intelligent life extremely difficult, if not impossible.
Super earths could also be prone to attracting more gas and thus have much thicker atmospheres
than here on our regular old dumb earth.
A much more dense atmosphere comes with a whole host of problems, and we need only look
at Venus for one very good reason why a super earth with a thick atmosphere would be uninhabitable.
Temperatures on the surface there are hot enough to melt lead, and while the planet
is closer to the sun than we are, it is still well within the habitable range of our sun.
Venus' thick, oppressive atmosphere is the real reason for its uninhabitable surface
temperatures, and a super earth with a similarly thick atmosphere would likely suffer from
the same life-killing global warming effect.
Another nail in the coffin for super earth habitability is the effect of the planet's
mass on its core.
Our own core is only partially molten, and its rotation maintains a powerful electromagnetic
field which protects life on earth from cosmic radiation.
On a super earth though, the massive pressures at the core from the increased mass of the
planet makes it extremely unlikely that its core would remain liquid for very long- perhaps
only a couple of billion years before it inevitably solidifies into a solid core.
While life could certainly evolve during the time the core was liquid, it would very quickly
find it difficult to survive as the planet's magnetic field weakened and eventually collapsed
entirely.
DNA is very delicate, and while some radiation is good to promote mutations that can spur
on evolution, too much radiation leads to the breakdown of DNA.
Life on a super earth with a solid core would likely only be very simple, and only exist
in places shielded by cosmic radiation.
However, it's not all doom and gloom and super earths could possibly give rise to a void
ecology- or life that exists in outer space.
We know that there are organisms from our own planet that can exist for a short time
in space, so the idea of a void ecology is not completely out of the question.
However, the problem with looking for space-faring lifeforms is that as far as we know it, life
cannot get started in the extremely harsh environment of space.
It must start somewhere more hospitable, and then make the move to space.
Super earths with solidifying cores could be the perfect nursery for a void ecology,
with organisms becoming increasingly resistant to cosmic radiation via the slow, multi-million
year process of the planet losing its magnetic field.
All it would take then is a lucky asteroid impact to knock debris infected with these
lifeforms into outer space, an improbable, but not impossible proposition.
However, for life as we know it, super earths are looking increasingly unlikely to be hospitable.
But, scientists have high hopes for a class of super earths that range in the low end
of the scale, with mass only twice as big as our own earth.
These smaller super earths have many of the advantages of larger super earths- climate
stability, longer molten core life span, larger surface areas- without the disadvantages of
being as big as their larger cousins.
These super habitable worlds may end up being havens for life, even intelligent life- though
the increased gravity would make rocketry more difficult and expensive, perhaps greatly
delaying or even preventing a species from ever making it into space.
Earth may turn out to be a backwater planet that's barely habitable by alien standards,
but seeing as it's the best we've got in our galactic neighborhood, we'd better start taking
problems like global warming and pollution seriously, because there's nowhere to run
to.
Now go watch Space Chief Makes Shocking Alien Confession, or click this other video instead!