Does Life Exist Elsewhere in the Cosmos?

Artist's Concept of Nearest Exoplanet to Our Solar System Around Epsilon Eridani
Artist's Concept of Nearest Exoplanet to Our Solar System Around Epsilon Eridani. NASA, ESA, and G. Bacon (STScI)

The search for life on other worlds has consumed our imaginations for decades. Humans feed on a constant supply of science fiction stories and movies such as Star Wars, Star Trek, Close Encounters of the Third Kind, which all cheerfully suggest that they are out there. People find aliens and the possibility of alien life are fascinating topics. But, do they really exist out there? It's a good question.

How the Search for Life Is Done

These days, using advanced technology, scientists may be on the verge of discovering places where life not only exists but may well be thriving. Worlds with life on them may be all over the Milky Way Galaxy. They could also be in our own solar system, in places that aren't exactly like the life-friendly habitats that exist here on Earth.

It's not just a search about life, however. It's also about finding places that are hospitable to life in all its many forms. Those forms may be like the life that exists on Earth, or they could be very different. Understanding the conditions in the galaxy that enable the chemicals of life to assemble together in just the right way. 

Astronomers have found more than 5,000 exoplanets in the galaxy. These are worlds circling other stars. There are many more "candidate" worlds to be studied. How do they find them? Space-based telescopes such as the Kepler Space Telescope look for them using specialized instruments.

Ground-based observers also look for extrasolar planets using very sensitive instruments attached to some of the world's largest telescopes. 

Once they find worlds, the next step for scientists is to figure out if they are habitable. That means, astronomers ask the question: can this planet support life?

On some, conditions for life could be quite good. Some worlds, however, orbit too close to their star, or too far away. The best chances for finding life lie in the so-called "habitable zones". These are regions around the parent star where liquid water, which is necessary for life, could exist. Of course, there are many other scientific questions to be answered in the search for life. 

How Life is Made

Before scientists can understand if life exists on a planet, it's important to know how life arises. One major sticking point in discussions of life elsewhere is the question of how it gets started. Scientists can "manufacture" cells in a laboratory, so how hard could it really be for life to spring up under the right conditions? The problem is that they are not actually building them from the raw materials. They take already living cells and replicate them. That's not the same thing at all.

There are a couple of facts to remember about creating life on a planet:

  1. It's NOT simple to do. Even if biologists had all the right components, and could put them together under ideal conditions, we can't yet make even one living cell from scratch. It may very well be possible someday, but not now.
  1. Scientists don't really know how the first living cells formed. Sure they have some ideas, but no one has replicated the process in a lab. 

What they do know are the basic chemical building blocks of life. The elements that formed life on our planet existed in the primordial cloud of gas and dust from which the Sun and planets arose. That would include the carbons, hydrocarbons, molecules, and other "pieces and parts" that make up life. The next big question is how it all came together on early Earth to form the first one-celled life forms. There's not a complete answer to that one, yet.

Scientists know conditions on early Earth were conducive to life: the right mix of elements was there. It was just a matter of time and mixing before the earliest one-celled animals came about. But, what was it that spurred all the right things in the right place to form life?

Still unanswered. Yet, life on Earth — from the microbes to the humans and plants — is living proof that it is possible for life to form. So, if it happened here, it could happen elsewhere, right? In the vastness of the galaxy, there ​should exist another world with conditions for life to exist and upon that tiny orb life would have sprung up. Right?

Probably. But no one knows for sure yet.

How Rare is Life in our Galaxy?

Given that the galaxy (and universe) for that matter, is rich with the basic elements that went into creating life, it's very likely that yes, there are planets with life on them. Sure, some birth clouds are going to have slightly different mixes of elements, but in the main, if we're looking for carbon-based life, there's a good chance it's out there. Science fiction likes to talk about silicon-based life, and other forms not familiar to humans. Nothing rules that out. But, there's no convincing data showing the existence of any life "out there". Not yet. Attempting to estimate the number of life forms in our galaxy is a bit like guessing the number of words in a book, without being told which book. Since there is a large disparity between, for instance, Goodnight Moon and Ulysses, it is safe to say that the person doing the guessing doesn't have enough information.

That may seem a bit depressing, and it's not the answer everybody wants. After all, humans LOVE science fiction universes where other life forms are teeming out there. Chances are, there is life out there.

But, just not enough proof. And, that raises the question, if there IS life, how much of it is part of an advanced civilization? That's important to think about because life could be as simple as a microbial population in an alien sea, or it could be a full-blown space-faring civilization. Or somewhere in between. 

However, that doesn't mean there isn't any. And, scientists have devised thought experiments to figure out how many worlds might have life in the galaxy. Or the universe. From those experiments, they've come up with a mathematical expression to give an idea about how rare (or not) other civilizations may be. It's called the Drake Equation and looks like this:

N = R* · fp · n·f·f · f· L.

where N is the number you get if you multiply the following factors together: the average rate of star formation, the fraction of stars that have planets, the average number of planets that can support life, the fraction of those worlds that actually develop life, the fraction of those that have intelligent life, the fraction of civilizations that have communications technologies to make their presence known, and the length of time that they've been releasing them. 

Scientists plug numbers in for all these variables and come up with different answers depending on what numbers are used. It turns out there could be just ONE planet (ours) with life, or there could be tens of thousands of possible civilizations "out there." 

We Just Don't Know — Yet!

So, where does this leave humans with an interest in life elsewhere?

With a very simple, yet unsatisfying conclusion. Could life exist elsewhere in our galaxy? Absolutely.

Are scientists certain of it? Not even close.

Unfortunately, until humanity actually makes contact with a people not of this world, or at least begin to fully understand how life came to exist on this tiny blue rock, the questions about life elsewhere aren't going to be answered. It's most likely that scientists will find evidence of life in our own solar system first, beyond Earth. But, that search requires more missions to other places, such as Mars, Europa, and Enceladus. That discovery may come about much faster than the discovery of life on worlds around other stars. 

Edited by Carolyn Collins Petersen.

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Millis, John P., Ph.D. "Does Life Exist Elsewhere in the Cosmos?" ThoughtCo, May. 10, 2018, thoughtco.com/does-life-exist-elsewhere-in-galaxy-3072592. Millis, John P., Ph.D. (2018, May 10). Does Life Exist Elsewhere in the Cosmos? Retrieved from https://www.thoughtco.com/does-life-exist-elsewhere-in-galaxy-3072592 Millis, John P., Ph.D. "Does Life Exist Elsewhere in the Cosmos?" ThoughtCo. https://www.thoughtco.com/does-life-exist-elsewhere-in-galaxy-3072592 (accessed May 25, 2018).