Post by AJ Rise:
Are we alone in this universe? Where are the space aliens? What do they look like? When, if ever, will we get to meet them? These questions all relate to the holy grail of astrobiology: discovering an intelligent alien species. Countless scientists and philosophers have attempted to tackle the question of alien life, and thus many brilliant works have been produced on the subject. Here, we explore what we know about the possibility of alien life, and offer our own insights about its possible origins and locations.
A well-known attempt at predicting the probability of discovering extraterrestrials comes from Dr. Frank Drake’s famous equation, N = R x fp x ne x fl x fi x fc x L. Each term represents the probability of a specific requirement for intelligent life to develop in a star system. The product of these terms is then multiplied by number of stars in the galaxy R and the time in which an intelligent civilization is actively using technology to signal its presence in some kind to the cosmos L. The result is a prediction of the number of “contactable” species in our galaxy at any given time. However, each contributing factor is so difficult to guess that the number of intelligent races in the Milky Way Galaxy has been predicted to be anywhere in between 9.1×10^-11 (we are almost certainly alone) and 15,600,000 (more than anyone ever dreamed). The range in the order of 1019 species per galaxy means no useful information can be mined from the equation without developing an accurate understanding of each individual parameter.
Nevertheless, 15,600,000 can serve as a well-reasoned upper estimate for the number of alien civilizations within our galaxy. There are 250 billion (+/- 150 billion) stars in the Milky Way, which suggests that, at most, there is a single alien civilization per 16,025 stars at this exact time (the lower estimate yields a value of one civilization per 2.7 sextillion stars). Nobody is saying with complete certainty that humans will never encounter alien species, but the math suggests that such an event would be a stunning coincidence without the prior exploration of billions of star systems.
Despite the evident rarity of highly intelligent life, recent studies have had powerful implications, suggesting that simpler, microscopic life forms might be more common than we realize.
In the western Pacific Ocean, sandwiched neatly between Guam and the Philippines, lies the deepest point on the ocean floor: the Marianas Trench. This seabed is perhaps the most hostile environment on earth. Eleven kilometers of water exerts a pressure exceeding 15,000 pounds per square inch on the floor of the abyss (for reference, the atmospheric pressure at sea level is 14.7 psi, roughly a thousandth of the pressure in the trench). No light can penetrate anywhere near its depth, locking the chasm in eternal night. The temperature ranges between 1 and 4 degrees celsius – just above freezing. For years after its discovery in 1875, scientists assumed that no life could possibly survive in such a harsh environment.
It goes without saying that a team of researchers in March, 2013 was utterly flabbergasted to discover a vibrant microbial community; More vibrant, in fact, than most other areas of the ocean floor. Vast colonies of extremophiles (organisms adapted to thrive in any manner of extreme conditions) cluttered the dusty terrain. An entire ecosystem rose above the seemingly desolate wasteland.
After only brief speculation, it became shockingly apparent to researchers why the trench would be ideal microbial real estate. Without access to light of any kind the trench’s occupants are exclusively heterotrophic. Such miniscule ocean dwellers need little nutrition to sustain themselves. At the deepest point on the ocean floor, a nearly endless stream of dead sea creatures naturally drifts downward into the trench. It takes a lot of microbes to eat a whole fish, not to mention a giant squid or two, so naturally, colonies explode into vast populations surrounding the corpses of all sorts of marine life.
This discovery was succeeded by several others: microbes were found in tiny aquatic fissures in the earth’s crust, thousands of feet beneath the trench itself, the scorched wake of a volcanic eruption, and even endured adventures in the cold vacuum of space. In recent years, it has become apparent that life is capable of existing, and even thriving, in the most extreme conditions found on our planet. Microbes are far more adaptable than anyone thought possible, spreading to every corner of the planet.
In terms of astrobiology, discovering life at the bottom of the Marianas Trench has profound implications. If thriving ecosystems of microorganisms can evolve in such extreme environments here on earth, it stands to reason that life could thrive in any number of nasty extraterrestrial landscapes. In other words, alien life might be more possible than we think.
Bearing this in mind, it is worthwhile to explore the places within our solar system where life, as we might understand it, might exist. We’ve established that, once present, microorganisms are stunningly capable of spreading around a given environment, but in order for it to flourish on other worlds, it must have a starting place. Thus, I must begin with what we understand about the origins of life on earth.
I would broadly define living organisms as something that survives in its environment in order to reproduce and undergo Darwinian natural selection. Depending on who you ask, the definition can contain more nuance and exception, but you get the idea. On Earth, all life we know of takes the form of carbon-based, water dependant creatures whose hereditary information is stored in deoxyribonucleic acid (DNA). In general, DNA contains instructions for building proteins, which determine every aspect of the organism’s characteristics. In order for life to form on the ancient Earth, nucleic acids and proteins must have either formed within the conditions on site or been delivered to us.
Researchers at the National Academy of Sciences in the Czech Republic decided to tackle this problem my recreating the “chemical soup” on the surface of Earth during the time when life forms appeared, around four billion years ago. At the same time, the Earth suffered a cataclysmic event known as the Late Heavy Bombardment, in which Earth was pounded with debris. While some scientists believe these collisions may have wiped out previously existing life forms, many believe they were essential for providing the building blocks to life as we know it.
In 2001, a duo of Italian researchers suggested that formadine, a simple compound formed by the reaction of water and hydrogen cyanide, could be a possible parent compound for the necessary molecules of life. It would have been abundant on early Earth, and has even been identified in the tails of comets. This is the chemical the Czech scientists chose for their experiments.
The team created a chamber of the chemicals present on the surface of a younger Earth and used laser pulses to bring the “soup” to over 4,200 degrees Celsius, and introduced intense x-ray and ultraviolet radiation. The resulting molecules were remarkable: adenine, guanine, cytosine, and uracil, the four nucleotide bases in RNA, an essential chemical in gene expression and the believed precursor to DNA. The genetic material of all life on Earth is built from these precious bases.
This research is limited in scope and does not fully plot the formation of life on earth, but it does demonstrate that the conditions existed for RNA to be synthesized on an early earth. Because of the “pairing” nature of RNA bases, it is believed that adenine would bond with uracil, and guanine with cytosine, eventually forming polymers that replicate in an exact manner, the essential feature of modern biology. In short: life may have emerged from a chemical soup of just the right conditions.
It is also feasible to simulate these numerous environments within any number of commercial chemistry softwares, at varying degrees of sophistication. Many other relevant scientific conclusions have been reached from such techniques in several disciplines, from catalysis to astrophysics to materials science to pharmaceutical development. By specifying the parameters of the environment in which life probably formed, scientists may be able to predict even more steps in the origin of life as we know it.
On January 2nd, 2002, NASA’s probe Starchaser passed through the tail of the comet Wild 2 (pronounced vilt 2). It deployed a collection grid against the onslaught of the passing comet trail, made up of aerogel fitted between thin layers of aluminum foil. Over 99% air, this gel served as the perfect mechanism to trap passing particles of the trail, snagging bits of comet as it passed through the largely unexplored phenomenon. It then locked the valuable payload away, and dropped it down to the Utah desert four years later. The contents of the gel were sent to researchers all over the world, who carefully examined its contents. The results strongly suggest that the essential building blocks for life are present in space and all over the universe.
NASA’s Goddard labs was the first group to discover the amino acid glycine in the samples recovered from the comet. Isotopic analysis verified that the amino acid indeed came from the comet, and not human handlers. This was the first time discovering amino acids on a comet, and the first discovery of the fundamental building blocks of terran life outside the boundaries of our own planet.
This discovery has profound implications. Firstly, we know that our favorite organic molecules are not unique to the speck of dust we’ve found ourselves on. The presence of amino acids on comets also gives clues to how they may have been delivered to Earth. In the Late Heavy Bombardment, as well as previous collisions, comets could have provided the water and proteins needed to build simple microorganisms. If this long history of comets brought along enough water to fill our oceans today, they may have brought enough amino acids to, by chance, assemble simple creatures.
We now have something that resembles a recipe for life: amino acids + formadine + water + heat + radiation = a chance that life can develop and evolve. We know the ingredients are scattered, more or less randomly, throughout the universe. It stands to reason that, whenever all the ingredients converge into a single area, life as we understand it has a chance of emerging.
The many explorations of our solar system in recent decades have unveiled a series of environments which, while hostile to humans, have the potential to support diverse extremophiles. Much like the Marianas trench, Mars, Europa, Enceladus, Ganymede, Callisto, and even Titan are hardly the ideal place to build a vacation house, but might be the equivalent of the Bahamas for highly microbes.
When hearing the phrase “alien life,” many of us think about Mars. There was a time, not long ago, when blurry telescope images led us to believe its inhabitants are intelligent. Our current understanding of the red planet is certainly less optimistic, but there is mounting evidence that mars may possess life-supporting biomes as we understand them. The scarred, dusty surface possesses numerous canyons and valleys, clear signs that the planet was once teeming with running, liquid water.
As planets do, however, Mars has entered a newer, colder era, making liquid water on the surface impossible. Temperatures have highs of 20 degrees celsius and lows of beneath 150 degrees celsius, making it impossible for water to remain a liquid for more significant amounts of time. The atmospheric pressure is a mere fraction of earth’s, so any surface water evaporates instantly.
However, water is far from absent in its biome. Condensation was reported to collect on the descending Phoenix lander in 2008. In July 2018, radar technologies on the Mars Express Spacecraft detected a distinct, 20 km wide patch of subsurface liquid water near the martian south pole. Because of the low temperature and pressure, this liquid is likely highly saline, as dissociated ions in a solution depress the freezing point and elevate the boiling point. There are several examples of microbes on Earth that thrive in salty, cold water (chiefly in antarctica). The evolution of similar organisms on Mars is not inconceivable.
In 2004, researchers announced the detection of methane in the Martian atmosphere. Because the thin atmosphere offers limited protection, methane will break down from intense solar radiation, indicating that some force produces it. In June 2018, NASA announced a cyclical variation in methane concentration, suggesting that something, possibly living, must be replenishing it as it depletes.
Mars is far from the only place in the solar system which possesses liquid water. The Voyager and Cassini missions demonstrated that Jupiter’s moon Europa and Saturn’s moon Enceladus have entire oceans beneath their solid outer shells. Deep in these buried waters, the conditions necessary for microbes to thrive might exist. In 2012, NASA’s Hubble Space Telescope observed water vapor above Europa’s south pole, and in 2022-2025, dozens scientific instruments will be sent to investigate on the “Europa Clipper” mission. The probe will provide detailed data on the nature of these subsurface oceans.
The number of locations to potentially discover life within our solar system increases if we consider the possibility that it may take a form fundamentally different to all life on earth, on a molecular level. What if, instead of water, its evolution depends on a different chemical? What if it can only exist at an entirely separate set of conditions? Researchers speculate there are a few conceivable, albeit unlikely, alternatives to biochemistry.
As an example, Saturn’s moon Titan is the only extraterrestrial world in our solar system with lakes on its surface. The problem: the lakes, along with much of the atmosphere, are made up of simple hydrocarbons, like methane, ethane, and propane. To all life on earth, substituting liquid water for liquid methane would be fatal, but if similar but distinct self-replicating molecules were formed early in the moon’s history, the course of Titanian evolution could have produced a thriving community of microbes, feasting on the same molecules we use to heat our stoves.
All this is a mere sampling of the detailed research and rich history surrounding the hunt for life in our solar system. Luckily, NASA has produced a series of public domain graphic histories, which wonderfully outline what we know so far about life at each point in the solar system. The art is also quite impressive. They can be found here: https://astrobiology.nasa.gov/resources/graphic-histories/.
The reader should be aware that astrobiology is an entire scientific field that is far from summarizable in a single blog post, and thus my intention is not to comprehensively list every breakthrough on the subject. Instead, returning to the questions with which I began, my intention is to provide my take on the question “Are we alone in the universe?” Many have asked tit, and at present there are multiple conclusions easily reachable through rational thought. There is more than one “right” answer (that is until we find the actual right answer). Based on the research presented in this article, however, I’d like to briefly present my take.
As evidenced by the fact that the human race exists, the probability of intelligent life forming in a given star system is miniscule, but not zero. The universe is really, really, really big. So big, in fact, that I believe that intelligent life is likely to develop at several places in space and time. Since the universe is so vast and lives so long, it would be a miraculous coincidence that two seperate intelligent species lived close enough to each other at times where their technological primes coincided.
It is much more likely that we may find microscopic, alien life in the various environments in our solar system. Microorganisms have repeatedly proven their ability to evolve their way into finding comfort in extreme conditions. Scientists have demonstrated that the conditions to create early life existed on a young earth, and it is likely that neighboring objects developed similarly (especially mars). The possibility of both the starting point and evolutionary journey for life elsewhere in our solar system are present. Finding an alien species certainly remains a tenuous matter of probability, but it’s not yet out of the question.
Sources:
https://en.wikipedia.org/wiki/Drake_equation
https://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html
http://www.pnas.org/content/early/2014/12/05/1412072111′
https://astrobiology.nasa.gov/resources/graphic-histories/
http://science.sciencemag.org/content/early/2018/07/24/science.aau1829.full
https://www.hydro-international.com/content/article/thirty-years-of-discovering-the-mariana-trench
https://www.jpl.nasa.gov/missions/europa-clipper/
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