Exoplanets (and life?) in the Goldilocks Zone

This one is for all the geeks out there in these fora

.

Whether life on Earth is a unique phenomenon or something that has emerged before or will emerge later in other parts of the universe is a question that has of course intrigued mankind for probably as long as the species has existed. (In the early history of humanity, "other parts of the universe" could just mean "over that mountain range" or "on the other side of this lake.")

This is the topic of this thread, so after we're done we can just call science and tell them we got it figured out.

I'll start with some basics of the history of cosmology to establish some context, and while I'm doing that I'll open up some concepts that might still be unfamiliar.

We humans used to believe that we were something special. Many religions were partially based on the idea that life on Earth is a unique phenomenon, and many religions have had to endure great internal conflict when discoveries that go against this idea have been made.

Originally, we thought that everything on Earth was made for us and that the Earth was the centre of the universe, and everything that we saw in the night sky was either spread out over us (like a dome) or circling around us. These beliefs were of course replaced by a more accurate picture of the Solar system as science did its thing and exposed the reality.

We no longer think that humans were planned or that everything on Earth is meant for us; instead, we know that our species is, like all other species, a result of evolution by non-random natural selection, and thus every feature of us is a result of that process.

This means that we were not designed, but came to be by natural processes - which removes us from our position as the purpose of the Earth and places us as a species among others living in a changing environment that it can manipulate to a degree. We can still claim dominion over the Earth, but we now know that we're the only ones who care and that nature ultimately controls our destiny more than we control nature.

We also know now that the sun doesn't go around us, and that we are just one planet going around the sun. We used to believe that there were no other planets, but we were proven wrong. We used to believe there were no other Solar systems, but we were proven wrong; then some of us believed that our galaxy was the only one, but once again, the reality was entirely different.

From these paradigm-shifting discoveries arises a pattern: "every time we put ourselves on a pedestal, we get taken down." Every time we thought we were unique, we found out that we're very tiny and (in a sense) insignificant compared to the rest of the universe. This history has led scientists to conclude one of the central concepts that one needs to understand to know what this thread is about: the Mediocrity Principle.

The Mediocrity Principle states that the parts of the universe that we've observed so far are in a general sense like the rest of it. There's nothing special about the parts that we've observed, and the more we discover, the more average our corner of the universe seems.

This is important because it is this principle that allows scientists to make estimates about the number of galaxies in the universe or the number of stars in a galaxy and so on - we observe what we can and generalise from there. Some of these generalised results can then be confirmed by observation.

(To give an example, we could extrapolate from the amount of stars in some pre-determined region of the Milky Way the general concentration of stars in similar regions and predict how many we should spot with a telescope of a certain type if we observed a certain region for a certain time, and then when we do the experiment it should check out.)

Before I go on, I should define "exoplanet" because it seems I didn't manage to shoehorn it into the part where I talked about the historical delusion that there were no other star systems.

An exoplanet is a planet that is not in our star system. That means that it probably orbits another star (or two stars that in turn orbit their shared centre of mass, in the case of a binary system.)

With our current equipment, it is very hard to directly observe an exoplanet, but if one comes between its star and our point of view (be it Earth or a satellite,) we get a nice eclipse of the star. Another way to observe them is to follow the star's movement very carefully and see if it wobbles in a regular pattern. If it does, it means it has a satellite (or possibly more.)

I see that there's one more concept from the thread title that I need to explain, but to do that I'll have to talk a little more about the Mediocrity Principle.

When we search for extraterrestrial life or planets we could potentially colonise in the distant future, we're looking for planets that have certain features that could support life as we understand it. We can't look very effectively for other types of life, as we can't give more than educated guesses as to what other kinds of life there could be.

What we're looking for in an exoplanet (if we're looking for life, that is,) is liquid water. It is thought that liquid water is a fundamental prerequisite for the emergence of life. Once we find that, we can look for signs of the influence of life, such as a high concentration of oxygen in the atmosphere.

(The high oxygen content of our atmosphere is a symptom of life that emerged not long after life itself got started. Well, "not long" in a relative sense: the earliest fossils are 3.5 billion years old, or approximately a billion years younger than the Earth itself; and a mere 1 billion years later, life was wide-spread enough and photosynthesis was active enough that signs of this were left in the sediments that were formed during that time.)

Anyway, when we're looking for liquid water, what we want to find is a planet that is not so close to its star that the water boils, and not so far from it that the water would freeze. If a star's orbit is too unsteady (in the sense that its distance to its star varies too much,) it'll go from too hot to too cold, so that's not good either.

So we want a planet that has a steady orbit in what is called the Goldilocks zone, the range of distances to the star where liquid water can exist on the planet's surface.

I got the idea to create this thread from this BBC article about a recent discovery that there are probably billions of planets the size of which ranges from 1 to 10 times the size of the Earth orbiting red dwarf stars in their respective Goldilocks zones.

The people who did the research say that "about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet. ... Because red dwarfs are so common - there are about 160 billion of them in the Milky Way - this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone."

It has earlier been estimated that there are about 100 billion galaxies, and an average galaxy has about 100 billion stars. With this alone, it could be fairly safely conjectured that there would be tens or hundreds of billions of planets in the Goldilocks zone of their star.

I look forward to talking about the possibility of life in exoplanets in the Goldilocks zone in this thread.

edited 28th Mar '12 4:52:48 PM by BestOf

Quod gratis asseritur, gratis negatur.

Of course, our understanding of what is habitable for life comes from an understanding of Earth-based life. Life on Earth has evolved around Earth conditions, nothing about that makes these conditions special. Especially not for fast-evolving, ultra-adaptable bacterial lifeforms.

And let us pray that come it may (As come it will for a' that)

That is true.

Still, I think it's wonderful that even if we limit ourselves to very specific conditions, we still have billions of candidates for life.

Quod gratis asseritur, gratis negatur.

Relevant to the discussion.

10 billion Earth like planets may exist in our galaxy alone

Who watches the watchmen?

Gotta love the ramifications of simple statistics on the galactic scale.

Share it so that people can get into this conversation, 'cause we're not the only ones who think like this.

And the chances of us visiting them in a time frame that is comprehensible to any human currently alive today is fairly miniscule. Even if you allow for [relatively] easy interstellar travel — not a guarantee if we can't figure out FTL — there's the problem of a time scale to consider.

In the thirteen-plus billion years that this universe has been in existence (again, disregarding the question of past or future iterations or alternate universes), human beings have had the capability to reach beyond our planet in any form for less than one hundred of those. We don't know that we'll continue to have that capability for even the next hundred at the rate we're messing up this planet.

Even if you assume that the lifespan of a species capable of interstellar travel and/or colonization is in the thousands or tens of thousands of years, that means that our nearest sapient neighbor could have risen to power and subsequently vanished a mere ten thousand years ago — or ten thousand years from now — in either case less than a thousandth of a percent of the age of the universe, and we'd never know they existed.

Let's take things a step further and postulate that, once a species reaches a certain level of achievement, it can live indefinitely by spreading from world to world, colonizing and populating each in turn, with sufficient cultural and technological achievement to avoid self-destructing. The likelihood of such a species already existing is far greater than that we just happen to be the first on the scene. All the good real-estate would be taken long before we bumble and stumble our way out there, and if we did, it wouldn't be your typical Space Opera Humans Are Special dealie. No, we'd be at a disadvantage comparable to one of those isolated Amazonian tribes stumbling upon a First World city, or possibly that of an earthworm inching its way painfully onto a hot sidewalk on a sunny day.

We can hope that a species capable of expanding across a galaxy would be a benevolent deity to us. I'm not sure that it's something I'd care to bet the existence of my own species on, though. One thing is for sure — they'd know about us long before we know about them.

edited 28th Mar '12 7:51:05 PM by Fighteer

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Of course, the idea of an Empire expanding across the stars might only be a human thing. An extraterrestrial civilisation that has followed a completely different biological and sociological path might have no concept of such a thing.

And let us pray that come it may (As come it will for a' that)

About this: the Papal astronomer is open to the existence of extraterrestrial intelligent life (and, even though I cannot find a quote in English, also stated that if an alien asked him to be baptized, he would certainly do that. Might prove tricky if the alien lives at temperatures at which water is not liquid... )

Personally, I think that life in exoplanets is a near-certainty. No idea about the likelihood of the evolution of intelligence, but I'm certainly open to the possibility.

EDIT: This is a source for the baptism quote I was thinking of (and contains much awesomeness besides.)

edited 28th Mar '12 9:06:02 PM by Carciofus

But they seem to know where they are going, the ones who walk away from Omelas.

Something tells me that Humanity would start BUILDING custom "planets" long before trying to colonize naturally occuring planets that just happen to be hospitable to life (human life anyway) outside the solar system.

As mentioned above, the distance needed to be travelled, the time it would take, even with the possible advent of advanced propulsion systems ala FTL are daunting challenges.

Sattalites/space stations though, are old and proven to be workable (if crude compared to the requirements) technology.

It is a much smaller leap to me, to simply create a sustainable biosphere in space some time this century, than treking through the stars (PUNS) looking for a place to colonize.

edited 2nd Apr '12 8:11:47 AM by Natasel

I think that a better approach would be to modify the human body in order to make it more adaptable to extreme environments. It strikes me as more feasible than, you know, building custom planets.

But they seem to know where they are going, the ones who walk away from Omelas.

Well, too much modding removes the "human" trait.

While I would certainly love to modify my current bio-design, I'm not sure I want to go so far as to be another species.

Besides, we've already done things like make a livable Space Station. Creating a new breed of human that is say, resistant to the degradation of a low G environment has not been done yet as far as I know.

And then the colonies will start a war of independence using giant robots? I'm up for that.

To be honest though, at least building giant space colonies, while probably very expensive and technically very difficult, it doesn't need to go around certain laws of physics.

edited 28th Mar '12 11:46:08 PM by IraTheSquire

I read an interesting (although I didn't agree with it) article arguing that if we find extraterrestrial life, we are monumentally screwed due to a "Great Filter". Hang on, will try and find it.

Here it is

edited 29th Mar '12 12:04:37 AM by pagad

With cannon shot and gun blast smash the alien. With laser beam and searing plasma scatter the alien to the stars.

...for a given definition of "Earth like planet".

Sorry. Somebody has to be the space skeptic in discussions like this

Unbent, Unbowed, Unbroken. Unrelated ME1 Fanfic

No matter how you cut the numbers, statistics indicate an overwhelming likelihood that there are many planets with environmental parameters similar to ours in our galaxy. The point I'm trying to make is that you have more dimensions in the equation than proximity and density. Time is another major factor. We could miss another sapient spacefaring species by a mere thousand years and never know they existed — and that's less than a ten-millionth of the age of the universe.

If someone had sent a probe by this solar system a thousand years ago to scan for life, would they have found humans or thought of us as anything worth investigating?

edited 29th Mar '12 7:25:41 AM by Fighteer

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Personally, I'm not expecting that we'd ever come across life on another planet - or if we do, it'll probably have died off long before we turn our disappointed looks to their fossils.

The Universe is so huge and old that even if life is likely (as it might turn out to be when we discover how it started,) it'd still be almost impossible for two instances of life to exist so close to each other as to ever meet.

If we find planet in the near vicinity of Earth, it's fairly likely that it'll be like life on Earth - because the life on either planet has spread to the other.

We've already found stones in the Antarctic that were from Mars and had some chemical prints that, it was originally thought, were most likely formed by bacterial activity. It was later discovered that some non-organic chemical reactions can cause those prints, so this time it probably wasn't life.

But still, we know that some forms of life could be carried to other planets if they're blown off their own planet by a meteorite. So if we find life in the Solar system, it'll probably be related to us, as it currently seems that the origin of life is a rarer event than the survival of a micro-organism of a journey through space.

Quod gratis asseritur, gratis negatur.

There's a point - why haven't we been dumping bacteria on, say, Mars or the Moon to see if it survives? If it can reproduce, adapt and survive over a period of time then we know that life, simple as it may be, can exist outwith Earth.

EDIT - also, A map of Space

edited 29th Mar '12 9:29:30 AM by TheBatPencil

And let us pray that come it may (As come it will for a' that)

This. The Golgilocks Zone is for what we might be able to terraform. Oxygen is only an indication of photosyntesis as we know it. I'm pretty sure there are ways to get energy that in no way involve oxygen. Water one kind of medium capable of carrying Stuff around the organism. Other liquids (or even gases) can do that.

This is a very valid point. But so far we're the only species we know to have advanced this far. This means we might just as well be talking about billions of years as tens of thousands. We haven't observed such a technologically advanced species develop and die, so we can only guess at their (or our) possible lifespan.

Yes. Though it might well go the other way around: we'll be colonizing planets and building new ones for half a billion years and then come across someone else. I just hope we recognise them for what they are, and are better at dealing with them than we were when finding each other.

Laws are made to be broken. You're next, thermodynamics.

There will be no "we" in half a billion years. I'd be surprised (so to say, if I weren't, you know, dead) if there'd still be a "we" in a thousand years... in any case, it's true that there might be other life out there. Maybe tellingly I thought in different veins: That for all the "Earth like" planets out there, there is most likely no planet so alike Earth that we could just so settle it.

Unbent, Unbowed, Unbroken. Unrelated ME1 Fanfic

Of course. If the lifespan of an expansive, colonial spacefaring species is indefinite (or at least in the millions or billions of years), it is almost a given that we'll encounter one or more of them eventually. For us to be the first would be a very statistically improbable occurrence. There's also the classic Precursors scenario where the first species raises up others to join it in an Uplift style chain of succession.

Again, simple probability dictates that we aren't unique. Given that our existence proves that the conditions for sapient life can evolve somewhere, it is overwhelmingly probable that they have done so multiple times. Of course that precise Earth duplicate could be tens of thousands of light years away, which for us in our current knowledge of the universe might as well be a billion light years.

edited 29th Mar '12 9:50:05 AM by Fighteer

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Well I don't think there is a planet out there that we could just land into and step out of the space ship without any protective gear on and just start building homes. That sounds exceptionally implausible to me. Instead, there might be planets that could be terraformed (assuming a shitload of technology we can hardly imagine now) with such low expenses that it'd actually be worth it in the long run.

Quod gratis asseritur, gratis negatur.

Regarding the first: Do we have any proof of that? Have we found any sign that other compounds are capable of self replication outside of the temperature ranges that normal amino and nucleic acids perform best? Are there any other liquids at other temperatures that behave as water does? I concede that the absence of such proof is not enough to prove that there are and can be no such compounds, but without it it seems frivolous to speculate which non-earthlike planets could be capable of life.

Personally, I find the idea of that not happening at least once monumentally less likely than it not happening at all.

edited 29th Mar '12 9:56:20 AM by OhnoaBear

"The marvel is not that the Bear posts well, but that the Bear posts at all."

I think if there's any chance we're going to colonise a planet, it's going to be Mars. The technology development necessary to undertake such an endeavour is of course huge, but orders of magnitude lower than attempting extrasolar colonisation.

Besides, it's hard not to look at this image◊ and not get a little starry-eyed.

With cannon shot and gun blast smash the alien. With laser beam and searing plasma scatter the alien to the stars.

I question if we have anywhere near the material to do that at all, much less anytime soon.

"The marvel is not that the Bear posts well, but that the Bear posts at all."

Well since I've been repeating stuff that Lawrence Krauss likes to talk about pretty much all the way through this thread, I might as well go on doing that.

When I mentioned that we've found stones from Mars in the Antarctic, it might occur to some to ask why Antarctic should be the best place to look for those stones. The reason is fairly obvious: because Antarctica is almost entirely white, so stones of darker colours really stand out.

There's an analogy that is often used when talking about these things: "a guy was walking to his car very late one night and noticed that his keys were missing. Assuming that he'd dropped them, he started going back the way he came, looking very carefully under each street light."

The point is that sometimes you can only look at the places where there's some hope of finding what you're looking for.

This is what we're doing when we're looking for Goldilocks zone planets: there might be life on some of the planets we're ignoring, but we'd probably not notice it 'cause we don't know how and where to look. The only place that we can look at and hope to find anything is the place that we can actually study. Therefore, Goldilocks zone is what we're looking at.

edited 29th Mar '12 9:57:41 AM by BestOf

Quod gratis asseritur, gratis negatur.