Astrobiology: The search for Extraterrestrial life/ About universe.

 Astrobiology: The search for Extraterrestrial life.

Introduction.

It’s Professor Dave, let’s find some aliens. Throughout this series we’ve achieved apretty good sense of the size of the universe. Whereas the ancients thought it was just the solar system and a sphere of bright lights rotating around us, we eventually understood the true scope of the Milky Way galaxy, with its several hundred billion stars, many of which probably have one or more planets just like ours does.

About universe.

Then about a century ago, we realized that our galaxy was just one of many billions of other galaxies, and our universe grew to an unfathomable size.

 

Place where life developed.

We know of one place for sure that intelligent life developed, that’s here on earth. But

Is there life anywhere else?

No matter how unlikely you think abiogenesis is, which is life being generated spontaneously from non-living matter, even if you think it’s a one in a billion shot, there are billions of worlds in our galaxy alone, and when you combine infinitesimal odds with impossibly large numbers, you get near certain probabilities for even the unlikeliest of things. In a nearly endless universe, there are nearly endless worlds, and it would be hard to believe that we are really the only ones. How many intelligent civilizations are out there.

 

Some questions about aliens.

 

1-       Trying to understand the cosmos just as we are?

2-       Where are they?

3-        What do they look like?

4-        What are their problems?

5-       What do they want?

6-       What do they fear?

7-       Do they have art?

8-       Will we ever meet?

 

I can’t imagine what could possibly be more fascinating than these questions, and there are a lot of scientists who agree with me, which is why they decided to study astrobiology.

 

Astrobiology.

This is the study of life in the universe, where it might exist and in what conditions, as well as how we might be able to detect it. Essentially, the search for aliens.

 

Let’s talk a little bit about what astrobiologists have come up with.

And some of the best candidates we know of for worlds that may already harbour complex life forms. First of all,

 

What are the conditions necessary for life to exist?

If we think about life on earth, we know that liquid water was absolutely critical. This was the medium within which the first organic molecules underwent endless chemical reactions until stumbling upon a self-replicating structure by chance. No solvent, no chemistry, no life. So it seems that liquid water is a must. And in order for liquid water to exist on a planet, the planet must be within the so-called habitable zone around its star. That is the range of distances from the star within which any ambient surface temperature ought to be between the melting point and boiling point of water, which allows for liquid water to exist on the surface of the planet.

 

But even in outlining these two simple criteria, if we think critically, we might realize that we are already getting overly presumptuous. Must a world truly be within the habitable zone of its star for liquid water to exist?

Europa and Enceladus

 We already know for sure that this is not the case. Remember when we talked about the Jovian and Saturnian systems, we saw that many of the moons of Jupiter and Saturn orbit their planet closely enough that the considerable tidal forces distort them such that there is a lot of friction inside these moons. That generates a lot of heat, enough heat to melt ice and get liquid water. We know with reasonable certainty that a number of these worlds contain oceans of liquid water, most notably Europa and Enceladus, and so it seems that solar radiation is not the only way to get an ocean.

 

Furthermore,

Who is to say that a liquid medium for life has to be water? Water works very well because it’s amphoteric. It can act as an acid or a base, participating in a variety of acid-base reactions that are biochemically relevant, allowing for biosynthesis.

Would something like ammonia work just as well?

 Ammonia could hypothetically perform the same function as water, it would just result in a kind of life that is stable at a dramatically different pH range. But we certainly can’t say that it is impossible.

1-     To get even a little more abstract, does life even need a liquid medium at all?

2-     Could life arise in clouds of interstellar dust that are rich in organic material?

 It seems difficult to imagine how it would work, but we can’t rule it out with certainty. Once we realize that life could potentially arise in a variety of different conditions, we begin to understand that life might be utterly commonplace.

 

Given our knowledge of the history of Mars, it is not outrageous to believe that simple unicellular life may have existed there in the distant past, and may continue to exist beneath its surface. Mars is literally our next door neighbor, and we also identified multiple moons in the outer solar system that seem ideal for life. With so many possibilities just in our tiny little nook of the galaxy, it seems that the Milky Way must be teeming with life. Now as to how often simple forms of life evolve to the intelligence of human civilization or greater is another story altogether. It might be the case that only one in a billion times does a world with basic forms of life produce a civilization capable of creating the technology needed to understand and explore the universe.

1-      So how many such civilizations exist in our galaxy?

2-       Five?

3-      Five thousand?

4-       Or maybe we are truly alone?

5-      What are the odds?

It may seem absurd to try to calculate the odds of such things, but that is precisely what astronomer Frank Drake tried to do in1961, with his Drake equation. It outlines a way to calculate N, the number of active, intelligent civilizations in the Milky Way, available for communication.

 

 So what are these variables?

 First we have the average rate of star formation. It’s difficult to conceive of life without a parent star, so that’s an important variable.

Next is the fraction of stars that have planets. Then, of those stars with planets, the fraction of them that can potentially support life. Of those, the fraction that actually develop life.

Of those, the fraction that develop intelligent life. Of those, the fraction that develop sophisticated technology with which to potentially communicate with us, and are perhaps actively sending signals through the galaxy. And finally, the length of time that such civilizations send such signals, which can be interpreted as the lifetime of the civilization.

This equation is obviously overflowing with speculation, as these variables are difficult to estimate without huge amounts of uncertainty. Therefore, it was not meant to be used to arrive at a rigorous value, but rather to provoke thought and discussion regarding the potential for alien life. It highlights key variables that are involved in such a search, and begs for their contemplation. And if we plug in a variety of estimates for these variables, the equation frequently yields results that tell us that it is rather unlikely that we are the only intelligent civilization in the galaxy, let alone the universe. There are those who are a little more pessimistic. Our star is a population one star, so there have been older stars capable of sustaining life for billions of years. If intelligent civilizations have existed for many millions of years longer than we have, it is likely they would have begun to colonize other worlds, a process that would move at an exponential rate, and it would seem like even one hyperintelligent race would quickly inhabit the entire galaxy. So in short,

 where is everybody?

 The fact that we can’t see or hear anyone is the essence of the Fermi paradox, which suggests we might be alone.

 Does the fact that we can’t see or hear anyone mean that no one is there?

 Not necessarily. Perhaps they are there, but rather than colonizing the galaxy, they have decided to retreat into their own technology, existing solely in virtual worlds and therefore no longer making any cosmic noise. Perhaps they are indeed everywhere but are leaving us alone, watching from afar to see if we become a civilization that is worthy of their attention.

 

Or maybe, just maybe, we really are the only folks in town. In the meantime, amidst all the speculation, an actual search is in progress. This search is multi-faceted, largely focused on searching for radio signals. This effort is called SETI, the search for extra-terrestrial intelligence. We’ve been listening since the 60s to see if aliens are trying to say hello, but there is just so much sky to listen to, and we can only listen in one spot at a time. Beyond this, there is the search for exoplanets.

 

These are planets outside of our solar system.

Orbiting other stars in our galaxy. These had been postulated for quite some time, but we had not actually detected one scientifically until 1988. Fast forward a few decades, and we have detected nearly four thousand exoplanets distributed amongst nearly three thousand systems.

 

How is that we find these things?

Well, we detect them in a number of ways, by measuring the difference in brightness of the star when a planet passes in front of it, by the wobble induced on the star as the star and its planets orbit around their collective center of mass, or other methods still.

 

What does this data tell us?

 First, we see that about one in every five stars like our sun has an earth-sized planet in its habitable zone. Think for a moment about how many billions of planets similar to ours that must exist just in the Milky Way.

 

1-       Is there life on these planets?

2-      Could we one day colonize them ourselves?

Incredibly, there is an exoplanet orbiting Proxima Centauri, which is the single closest star to ours, at just over four light years away. The possibilities for the next hundred thousand years of human effort are beginning to unfold. What will we do as our civilization grows, as we become capable of interplanetary, interstellar, or even intergalactic travel? To examine this, let’s move forward and talk about our future in space.