If a cataclysm strikes our planet, it would be nice to have a back-up plan somewhere out
there in the cosmos.
Whether we need to find a new home for our species because something has destroyed the
original or simply because we’re desperate to find life somewhere else among the stars,
other planets have long been a source of human fascination.
But have we already found what we’re looking for?
This is Unveiled, and today we’re answering the extraordinary question; have we found
Earth 2.0?
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The idea of an “Earth 2.0” generally refers to an alien world that is already Earth-like,
rather than a world that could be Earth-like with a little tweaking.
While planets within our solar system like Venus and Mars both offer similarities to
Earth in terms of their size, position and composition, we wouldn’t be able to safely
live on them without either closing ourselves off completely in high-tech, custom-built
habitats or greatly altering the planets themselves through terraforming.
For a true “home away from home”, then, we have to look farther afield than even the
icy moons of Jupiter and Saturn (which are also often tipped for human colonies one day);
instead, we have to broaden our horizons into different star systems entirely.
There are an estimated 100 billion planets in the Milky Way Galaxy.
And, according to some NASA forecasts, at least forty billion of these could be Earth-sized
planets, and eleven billion are Earth-sized planets orbiting a Sun-like star.
Considering we only have one confirmed, habitable planet at the moment - our own - a potential
eleven billion other worlds to explore certainly evens out the odds of us finding a second.
We call all planets found outside of our solar system “exoplanets”, with the first exoplanets
being discovered in 1992.
It sounds crazy now, but up until then we were working on assumptions that planets existed
elsewhere rather than irrefutable evidence.
Those first, ground-breaking worlds were located in the PSR B1257+12 system and were detected
by analysing the irregularities around a nearby pulsar, which is a pulsing neutron star.
Unfortunately, these particular worlds were much too radioactive to support life, but
their discovery motivated scientists to search for more and more planets like them.
One of the biggest operations to discover exoplanets came when NASA launched the Kepler
space telescope in 2009 solely with the aim of searching for planets orbiting other stars.
While the Kepler Program suffered some problems over its course, it ultimately succeeded in
its mission goals and operated for nine years before running out of fuel in 2018.
Over that time, it detected more than 2,600 planets and half a million stars, meaning
that in less than thirty years we’ve gone from zero verified exoplanets to thousands
of them.
Kepler worked by detecting “transits” in distant stars, which is when the light
they give off is blocked just a little bit by a planet traveling in front of them.
More than anything else before it, Kepler allowed us to build a comprehensive “map
of space”.
As such, one of our best candidates for Earth 2.0 was found in 2015 by Kepler; Kepler-452b,
which is often nicknamed “Earth’s Cousin”.
It’s a super-Earth predicted to be five times more massive than our planet, located
in the habitable zone of its star system around 1,400 lightyears away.
This isn’t close enough that we can just go over there and see for ourselves what kind
of planet we’re dealing with… but it’s not so far away that our most advanced telescopes,
like the Hubble space telescope, wouldn’t be able to get a better look at it.
Unfortunately, and perhaps surprisingly, however, as of early 2020 the Hubble telescope hasn’t
yet been used to investigate 452b - with other initiatives taking precedent.
That means that right now scientists aren’t at all in agreement about what we would see,
if we ever were to more closely monitor it.
We don’t even know for sure whether it’s a rocky planet like Earth or made of gas.
The SETI Institute - charged with the “Search for Extraterrestrial Intelligence” - has
also been trying to detect radio signals from 452b for some time in the hope that it might
be a source of alien life, but to no avail.
The confusion has led some to cast doubt on whether 452b even exists at all - although
a SETI study did estimate that there is between a sixteen and ninety-two percent chance that
the planet is real, which is quite a large margin of error.
Even so, scientists and star-gazers are well aware that in the hunt for “second Earths”,
with billions of worlds to choose from, it wouldn’t be pertinent to focus all our efforts
on one distant, debateable orb… and there are at least a few thousand other planets
we can and are taking a look at.
The closest, potentially Earth-like exoplanet to us is Proxima Centauri B. It’s only four
lightyears away, a much more reasonable distance, but it does also pose a few problems.
Chiefly, the star that Proxima Centauri B orbits around is a red dwarf star.
Red dwarf stars are the most numerous in the universe, but we’re not so sure what living
near to one would be like.
They’re much dimmer than yellow stars like our own sun, so any liveable planet would
theoretically need to be positioned much closer… which isn’t necessarily a problem, except
that a planet might need to be so close that it becomes tidally locked with its star.
We don’t think that this has happened with Proxima Centauri B, but we’re also not currently
sure whether Proxima Centauri B is even close enough to its star to be truly Earth-like
in the first place.
What is certain is that if any planet becomes tidally locked with the star it orbits around,
then it could no longer be considered as “Earth 2.0” material… because one side of it
would permanently face away from its chief energy source, in some senses creating two
worlds on one!
Another often-cited exoplanet in terms of the potential that it’s “like Earth”
is K2-18b, a planet that’s 120 lightyears away from us and one that was also discovered
by the Kepler telescope.
It’s much closer than 452b is and it’s predicted to have a similar temperature to
Earth; both promising qualities.
But, while it’s again orbiting a red dwarf star, it’s doing so very quickly - completing
a full orbit every 33 days, which is a year there for roughly a month here.
While scientists believe that it certainly is possible for red dwarf stars to support
habitable worlds, and that in fact a red dwarf system could even hold an advantage over our
own seeing as red dwarfs are so long-lived, to label K2-18b as “Earth 2.0” would still
be misleading.
Imagine just how different (if not unrecognisable) our planet would be if it were subjected to
a 33-day year!
With all of that considered, for something that could truly be a “new Earth” there’s
Kepler-186f.
For many scientists, it might just be the best candidate yet.
Once again discovered via the Kepler telescope, it’s roughly 550 lightyears away from us
but is comfortably inside the habitable zone of its star (another red dwarf) and it’s
not a super-Earth; its radius is only thought to be around 700 miles more than our Earth’s
is, and it’s thought likely that that this planet is rocky.
Upon its discovery in 2014, NASA confidently called it “the first Earth-size planet in
the habitable zone” - and it’s still our best bet in the eyes of many.
Kepler-186f is further away from its sun than we are from ours, but not drastically so - it’d
mean that the days would be a lot darker and colder there, but potentially not so cold
that we couldn’t survive.
If, one day, we ever devised a way to travel the 550 lightyears between us and it, then
we really could arrive at a “home away from home” - at least compared to anything else
we currently know that’s out there!
The one thing missing would be someone or something to share it with…
Because, if a planet was exactly Earth 2.0, wouldn’t that mean that it was already supporting
life of its own?
And, if that’s true - if it’s already, naturally populated - well, then we’ve got
a whole host of other issues on our hands, as well.
Because, as much as we might want to visit or relocate to a world where we wouldn’t
have to spend time, money and energy extensively terraforming it to our standards, would it
be morally correct to do so?
SETI could even strike gold and find incontestable signs of intelligent life before we even got
there, but what if that intelligent life doesn’t want to be disturbed?
Imagine the situation in reverse - that there’s another intelligent species on another habitable
world somewhere else in the universe, and they’re trying to locate another planet
that’s just like theirs, and that planet just so happens to be our Earth.
Would we really be fine with an alien race just showing up and rechristening our home
as just a “second version” of the one they’d left behind?
Probably not!
So, finding “Earth 2.0” and actually making plans to move there are two very different
prospects - the second of which involves the risk of harming an ecosystem that never asked
or wanted to be interfered with.
It’s an ethical debate that’s set to run and run.
On the one side, discovering other planets (Earth-like and not so) helps us to better
understand the universe; on the other, rather than finding a second home for humanity, we
should be focussing more on making Earth (our Earth) a better place before we abandon it.
In either case, there are plenty of exoplanets out there and it’s statistically probable
that at least a few of them should be able to host life, or even to precisely mimic conditions
on Earth.
Despite technological limitations and moral debate, the search for Earth 2.0 goes on and
on… and the list of potential candidates gets longer and longer.
What do you think?
Is there anything we missed?
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