We were impressed when we detected the first exoplanet, but how about detecting planets
in other galaxies?
As of right now, there are about 3700 confirmed exoplanets, most of which were discovered
by the Kepler spacecraft.
All of these planets are located in the Milky Way and, at our current technological viewpoint,
were relatively easy to discover since the majority of these exoplanets aren’t any
more than a few thousand light years away.
While it’s a reasonably easy task, we’ve only got 3700 exoplanets because the method
that the Kepler spacecraft uses, the transiting method, is a rather long process.
A harder task, however, is detecting planets outside the galaxy.
The nearest galaxy is the Andromeda galaxy, not counting smaller dwarf galaxies such as
the Magellanic Clouds.
At a distance of 2.5 million light years from Earth, it seems impossible to be able to detect
anything from galaxies so far away.
However, a month ago in The Astrophysical Journal Letters, they published the first
evidence of planets in another galaxy, one that is 4 billion light years away.
A group of astronomers used the data from a quasar about six billion light years away.
A quasar is an incredibly bright object, powered by a supermassive black hole in the centre
of galaxies.
From Earth’s viewpoint, the aforementioned galaxy that is 4 billion light years away
is in front of the galaxy that contains the aforementioned quasar, which is about six
billion light years away.
The light from the more distant galaxy—the one containing the quasar—travelled around
the closer galaxy and was magnified, allowing astronomers to get a closer look.
We were able to see it due to gravitational lensing, a phenomenon of General Relativity,
where a large mass, such as a black hole or a galaxy in this case, bends and magnifies
the light from objects behind them.
To see the extragalactic planets, they needed to use microlensing, a version of gravitational
lensing that is better suited for seeing objects as dim as planets.
The astronomers found evidence that there are about 2000 planets for every main sequence
star, ranging from the size of the Moon to Jupiter.
It seems that most of these planets are not orbiting a star, but rather travelling their
galaxy on their own as rogue planets.
We always assume that habitable planets, potential candidates that could hold and sustain other
technologically advanced civilizations, are always planets that orbit stars.
Rogue planets, or interstellar planets, could develop life, despite not having a star.
Technically, rogue planets are not planets at all because one of the necessities needed
to be classified as a planet is that it must orbit a star and well rogue planets don’t.
Another civilization, like ourselves, could develop on a planet similar to Earth and become
as advanced as we are today, perhaps even more advanced, then get ejected out of the
solar system and become a rogue planet.
As long as the planet has a few essential characteristics, some species could continue
to survive on the planet and adapt to suit it.
The main issue of not having a parent star is not having heat.
A planet could make up for that by having a core that maintains a liquid ocean, albeit
under a few kilometres of ice, as well as powering volcanic activity.
Additionally, a thick atmosphere would be helpful to maintain any existing heat and
pressure.
It could stay habitable for billions of years.
As there is no star nearby a rogue planet, no light reflects off the planet, apart from
background stars, and so details on the planet are hard to make out.
For this reason, rogue planets may be sought after by civilizations to be used as refuge
to hide from other, perhaps xenophobic, civilizations who may want to wipe them out.
If I want to end your civilization, the most obvious place to look is regular star orbiting
planets.
My civilization won’t bother checking every asteroid, comet and rocky body in the galaxy
for your civilization as it’s too time consuming.
The hiding civilization may also be so pre-cautious to send off smaller probes to other places
in the galaxy as seeds for their civilization, containing a colony of your people along with
every book digitally stored, every species on your home planet and so on.
So that, if the hostile civilization finds your civilization and you get wiped out, your
civilization will continue to live on, since you’ve got a smaller civilization elsewhere.
The hostile civilization will believe that they wiped you out and won’t search for
your other civilization.
This needs to be done in advance because if the xenophobic civilization finds you, they
will see your spaceships leaving and will hunt every single one down.
Extragalactic planets raises the question: will we ever be able to travel to other galaxies?
People tend to immediately assume that intergalactic travel is impossible, no matter how advanced
a civilization becomes.
It does make sense to assume this, both because of the huge distances involved but also because
interstellar travel is challenging to us, nevermind intergalactic travel.
In the future, that may well change.
Often in fiction, civilizations will have the ability to get to the other side of the
galaxy in only a few years, sometimes even in a few seconds.
Light is the fastest thing in the universe yet the distances between objects in space
are exceptionally long, so long that it takes light long periods of time to get from one
place to another.
From our perspective, it takes light 100,000 years to get from one side of the Milky Way
to the other since the Milky Way is 100,000 light years across.
If a civilization can get to the other side of the galaxy in a reasonable time, say one
year, getting to other galaxies won’t be much of a challenge.
There are a few reasons why you’d want to travel to another galaxy, and we shall cover
that notion in a future episode of the Fermi paradox series that discusses civilizations
that confine themselves to their home planet or solar system and, for whatever reason,
decide to not explore any further.
In that future episode, however, we will cover both reasons why a civilization would want
to explore space and reasons why one wouldn’t and not reasons why you’d want to go to
another galaxy but the reasons why a civilization would want to do either are pretty much the
same.
Comment down below your thoughts on extragalactic planets.
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