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!
