OPINION
The search for what we would deem to be "habitable" worlds orbiting
other stars has reached a crossroads in recent years. As our technology
and techniques improve, we've been able to identify small rocky worlds
orbiting within other stars' "habitable zones."
So far, we can measure an exoplanet's mass, understand its physical
size, even calculate its average density, revealing whether or not that
planet may contain quantities of water, for example. Add these factors
to our knowledge of that alien world's orbit and we are given
tantalizing clues as to whether liquid water may persist on its surface.
These apparently habitable worlds are quickly labeled "Earth-like," but they may not be like Earth at all. There's a lot more to our planet besides its mass and orbit that makes it habitable -- namely our thick atmosphere and protective magnetosphere, both of which safeguarded burgeoning terrestrial life around four billion years ago from the ravages of space weather.
Lacking sufficiently powerful observatories, we're not able to detect
atmospheres, let alone magnetospheres, around distant small exoplanets,
so the "Earth-like" moniker is premature at best.
But as we continue to discover all the weird, wonderful and extremely
varied exoplanets our galaxy has on offer, we're finding the potential
for worlds that may be considered "habitable" for short periods,
hypothetically allowing life (as we know it) to be sparked, only for the
habitable conditions in these worlds' atmospheres to dramatically
change, snuffing out the immature lifeforms.
An often-overlooked factor in the science behind the evolution of life is time,
and many of the exoplanets we've found may well be habitable during
short periods of their existence, but not long enough to allow life to
gain a foothold.
In an interesting discussion published in the journal Astrophysics and Space Science, Claudius Gros from the Institute of Theoretical Physics at Goethe University Frankfurt investigates the possibility of giving life a helping hand by blasting it into interstellar space and flinging our ready-made biology toward exoplanets that may only have a very short window of habitability.
"It is therefore certain that we will discover a large number of
exoplanets which are inhabitable intermittently but not permanently," Gros said in a statement. "Life would indeed be possible on these planets, but it would not have the time to grow and develop independently."
When basic life took hold on Earth, its very existence helped to shape
the habitability of our atmosphere. For example, bacterial mats changed
the chemistry of atmospheric gases, boosting its oxygen content and
facilitating the evolution of complex eukaryotic cells, upon which all
multicellular life is based.
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In Gros' discussion, he imagines sending a small interstellar probe to
another star system. On arrival, that probe would somehow slow down and,
using an on-board biological laboratory, would synthesize a selection
of single-celled organisms that would then be dropped onto a habitable,
yet lifeless world. Should this biological "Ark" of sorts seed the first
microbial life, potentially billions of years of evolution would have
been skipped on that world allowing life to take hold within the tight
window of opportunity, possibly allowing it to spawn a self-sustaining
alien ecosystem with a very terrestrial flavor.
"In this way, we could jump the approximately four billion years which had been necessary on Earth to reach the Precambrian stage of development out of which the animal world developed about 500 million years ago," he added.
This highly speculative method of seeding life is called, perhaps
unsurprisingly, the "Genesis Project" and Gros sees it as a means for us
to "give life something back."
Seeding life on other worlds is not a new concept; science fiction has
tackled it countless times and there are some scientific foundations for
the idea.
The mechanism known as "panspermia" is a hypothesis
that governs the transfer of life from one planet to another. Should a
massive asteroid hit one planet brimming with life, sending a chunk of
rock packed with living microbes into space, that rock may land on
another planet with some habitable qualities, allowing a few of the
surviving microbes that hitched a ride on the rock to make a new home.
But the mechanism described by Gros is a variation on the "directed panspermia" hypothesis
where an intelligent civilization wants to seed life on other worlds in
their image, sending biological capsules to spark their brand of life
elsewhere.
However, we quickly fall into an ethical trap. Just because we have
life on Earth, is it our biological obligation to share it with the rest
of the galaxy? Or would such an act be no better than biological
pollution or, even worse, a biological weapon? Just because we've got it, doesn't mean the rest of the universe wants it.
One obvious problem is the question of native lifeforms; say if a target world already has a rapidly evolving lifeform that's taken the opportunity to gain a foothold on that world? A Genesis Project capsule dropping on their heads filled with an out-of-the-box Earth BrandTM goo would be disastrous.
Though
Gros points out that great pains should be taken to ensure the target
planet isn't already inhabited, when talking about the potential
genocide of the foundational biology of a future alien race, it would be
hard to justify such a risky mission.
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