Planets that could sustain alien life much rarer than thought

Maybe we are alone after all: Planets that could sustain alien life much rarer than thought
Doyle Rice USA TODAY
Published 3:13 PM EDT Jun 11, 2019

An alien greets tourists and invites them to buy jerky, candy and T-shirts in Baker, California.
Jefferson Graham, USA TODAY
So, maybe we are alone after all.

The number of planets in the universe that could sustain alien life is much smaller than had been thought, astronomers announced this week in a new study.

“Imagine a habitable zone for complex life defined as a 'safe zone' where it would be plausible to support rich ecosystems like we find on Earth today,” said study co-author Timothy Lyons, a biogeochemist at the University of California–Riverside. “Our results indicate that complex ecosystems like ours cannot exist in most regions of the habitable zone as traditionally defined."

What's the problem? It turns out that a buildup of toxic gases in the atmospheres of most planets makes them unfit for complex life as we know it, the study said.

Traditionally, most of the search for planets capable of sustaining alien life has focused on what scientists call the “habitable zone,” which is where liquid water could exist on a planet’s surface. But, according to the new study, these planets would only be able to sustain very basic life, such as single-celled microbes – not complex creatures like animals, which include everything from simple sponges to humans.

So even though lots of planets may have liquid water, many of them have toxic atmospheres, the study authors said:

"To sustain liquid water at the outer edge of the conventional habitable zone, a planet would need tens of thousands of times more carbon dioxide than Earth has today," said NASA's Edward Schwieterman, the study’s lead author. "That's far beyond the levels known to be toxic to human and animal life on Earth."

Therefore, only about a third of the known "habitable" planets, of which scientists have discovered about 4,000, could sustain complex life forms like us.

“This is the first time the physiological limits of life on Earth have been considered to predict the distribution of complex life elsewhere in the universe,” said Lyons.

Schwieterman said that "showing how rare and special our planet is only enhances the case for protecting it. As far as we know, Earth is the only planet in the universe that can sustain human life.”

The study was published Monday in the peer-reviewed Astrophysical Journal.

 

To be fair this isnt that surprising to me, i already tought that complex lifeforms will be much rarer than microbes etc. Intelligent lifeforms would be even rarer than that, especially naturally occuring ones. Created, uplifted or assisted grown ones might be more common.

I wonder how rare intelligent life is in our galaxy. Given all the hurdles and the chance that they might destroy themselves before becoming spacefaring, i think at best there might be couple of hundred natural civilizations present at the moment, most of them probably way older than us.

 

It's an interesting article, But this is just a collection of his thoughts and opinions, Which in science doesn't mean a lot, This isn't peer-reviewed research which means, This is an opinion piece, It's a nice one too. But I wouldn't see the Drake equation circling the drain just yet.

If evolution holds true, Things we consider Toxic, possibly wouldn't be so, to other life forms that evolved in that environment. Oxygen is one of the most corrosive acids in abundance in the universe, it could destroy another kind of foreign carbon-based life form. Oxygen should be a deadly poison, yet life thrives in it.

 

Yeah i mean that title, its click bait. Ive never taken anyone seriously who tries to argue that we are utterly alone. Even if intelligent life were so exceedingly rare thered be just one civilization per a thousand galaxies, in the the vastness of the universe there would still be billions of them.

Also people forget the directed panspermia hypothesis. If a naturally occuring alien civilization evolves just once and passes "the great filter" and advances enough, they could begin to create all sorts of life in their galaxy if they wanted to, even intelligent ones, pretty much filling it with those given enough time.

 

The thing I focus on in my research is, Why are we humans so different from every other form of life we have discovered? I mean sure, There are Apes. But, When you really begin to study the difference we have to them, For instance, We have slightly longer lifespans on average, And this part can't be underestimated. We are vastly more mentally complex than apes, So even for the similarities, we are vastly different. There aren't any Gorillas having conversations as deep and meaningful as this.

We are complex unique creatures, In all the universe, As far as we have discovered. There is nothing else like us.

I think that's why we search so hard, Logically, We can't be alone in this manner or awareness and complexity. Because, I don't think we are looking for alien trees, frogs and bugs. We are looking for something like us.

 

Of course we are. We are social beings. Some like the idea of being alone, but i think for a lot of people the idea is terrifying. Thus we will try to cross oceans of time and space in our search, to find the answer, and maybe others have already done this and have gotten theirs. We just havent and cant get that far... yet.

 

In the past when we've done that we always found other humans waiting for us on the other side. I wonder how we'll feel if we encounter something exotic that we might or might not be able to communicate with.

 

So, odds looking worse for life as we know it, we think, is how I read it. There could still be something else out there very different from ourselves but, they may have lived and died long ago or be so far away it won't matter from our standpoint. To badly paraphrase Carl Sagan, it's overwhelming to think we might be it, it's overwhelming to think there might be something else (though to be fair I imagine there is something else, just, nowhere 'near' us.)

As for humanity being so different from other primates, I like this hybrid explanation: The Hybrid Hypothesis: Introduction

Always freaks me out though to imagine the gulf of understanding between say, ourselves and ants, and then think what if we do encounter an alien intelligence someday and there is as a similar gulf there, with ourselves playing the role of the ant this time. Would we even be able to recognize them as intelligent or would they seem like some natural disaster?

 

Well...

The big problem is that complex life didn't evolve until bacteria moved beyond being anaerobic.

An anaerobic organism can't get enough nutrition to form complex life.

And you need water - a universal solvent.

And carbon.

Multicellular Life on earth uses sugar/starches/fats to store energy.

The water on earth came from late bombardment.

It really looks like there is a very small chance (1:2000 or less) of a planet supporting life. It could be much much less. We haven't found another earth analog yet.

There may be something ammonia based on the gas giants - but it takes a lot of pressure and the life would be slower moving.

We might be the only earth-like planet in 500 light years.

 

So the literature so far has estimated roughly 20 billion Earth-like worlds in the habitable zone of their parent stars in our galaxy. If this is correct that number drops to about 13 billion Earth-like worlds in the habitable zone in our galaxy.

Even if only 1 in 200o such worlds actually support complex life, that's over 6 million worlds with complex life. And they are on average 2-3 billion years older than Earth...plenty of time for intelligent life to arise.

Chances that we're alone in our galaxy: ~0%

 

You are right on the money. There are 250 billion stars in the Milky Way. Just to make it more graphical: 250,000,000,000. That is more combinations that UK lottery, which is 1 in 14,000,000. If we said that every intelligent alien species won a lottery, there is 18,000 opportunities for intelligent life to get lucky.

Another thing that almost always gets forgotten, is there is a time aspect to the whole thing. Longer the galaxy's age, more time for rising of intelligent life there was. Milky Way is 12 billion years old and Earth is 4.5 billion years. That means, there was 12-4.5= 7.5 billions of years for life to evolve. As a matter of astrophysical fact, an average Sun like star in the Milky Way's habitable zone is 3.3 billion years older than Solar system.

Take that

 

This seems rather unimaginative.

Why couldn't there be life forms that flourish in the presence of gases that are toxic to living creatures on earth?

 

Well...

Yes but.

We still haven't found an analog for earth.

The earliest life are all extremophiles.

If not for mankind the planet was headed to such low levels of CO2 that advanced life would disappear. Plus we are losing our atmosphere.

The water mostly came from late bombardment.

And the distant gas giants and close in rocks arrangement of planets is unusual.

There are about 4003 known exoplanets. None similar to earth in the sweet spot.

Not sure how much the largest moon relative to its primary (other than Pluto) has affected things.

So even on earth complex life just made it in time.

A planet like Mars at best reaches the simple organism stage before it becomes uninhabitable.

And we still don't know what kickstarted life on earth.

The sun appears to be very low in variability compared to other stars.

There could be life out there, but it is closer to 5000 planets than 6 million.

If the impactor that created the moon struck later - the earth might have been uninhabitable. If the sun was more variable - the planet might get washed clean occasionally.

And the planets around red dwarves might not receive enough absorbable energy or are too close to primary (solar flare problems). There was a red dwarf that recently had a visible solar flare.

Further the planet would have to evolve something with a hand.

Which would require trees not shrubs.

Don't know - life is possible, but advanced life isn't that likely.

Given we haven't found anything similar the earth might be very rare. The closest is Kepler 452-b which is 60% bigger and has a gravity of 2 G.

But who knows?

 

Atmospheric Carbon Dioxide Greater 1.4 Billion Years Ago

Also the initial earths atmosphere was nitrogen and 10-10000 times the current CO2 level.

The original atmosphere when life developed was basically inert.

The oxygen in the atmosphere is the result of some Archaea trying to poison their competitors.

Venus has about the same amount of nitrogen as earth, just way to much CO2 (93 bar surface pressure).

 

That's meaningless, because our current technological limitations make it very very difficult to detect Earth-like worlds in the habitable zones of their parent stars. What matters is that we've detected enough planets now that we can analyze the data and determine with high confidence that there are over 20 billion Earth-like planets in the habitable zones of Sun-like stars in our galaxy alone.

Lol...where do you come up with this stuff? That's such a preposterous statement I can hardly believe that anyone could say that without laughing.

This is a chart of the atmospheric CO2 over the last 800,000 years - no sign of vanishing CO2 here:



And life has existed on Earth for 4.1 billion years. Mankind has been making a detectable impact on the atmospheric CO2 levels for roughly a century...and you're seriously trying to claim that for some crazy reason mammalian life would've suddenly run into an lethal drop in CO2 levels if we hadn't burned gigatons of fossil fuel and pumped the carbon dioxide emissions into the atmosphere like idiots?

Fish get their oxygen from breathing water.

Violin string used to be made from catgut.

The canals on Mars turned out to be canyons.

Relative to its size, the barnacle has the largest penis of any creature on Earth.

None of this is relevant but providing a list of statements creates the illusion of an argument.

Says who?

They may have figured that out actually. I read a good paper last year that attributed the Earth's early biogenesis phase to the high UV emissions coming from the young Sun - the UV ionized the amino acids, increasing chemical affinities and causing the rapid formation of complex organic molecules as the Earth was cooling, and setting the stage for life to arise almost as soon as the planet was cool enough to support it. These are common conditions with stars like ours btw.

Says you. I think we should wait until we can detect life around other stars before proclaiming any decrees about its prevalence. But if I had to place a bet on this, I'd bet that civilizations have arisen on more than 5000 planets in our galaxy so far.

 

The CO2 level keeps dropping as more CO2 becomes sediment (and the ocean cools).

There are 38,000 GT of carbon (CO2 counted as carbon only) in the ocean. It takes a while to turn that into sediment but the CO2 level is going to continue to decline.

Plus during the Jurassik period the air pressure was about 50% higher.

The CO2 level during the current ice age is the lowest it has even been in history.

Below 400-700 PPM C4 plants have an advantage. The first C4 plants started evolving about 6-7 million years ago.

Above 700 PPM C4 plants get outcompeted and go away (they have evolved during low CO2 periods in the past).

The point being that we weren't far from getting to 150 PPM where all plants start running into problems. They can't collect enough CO2. Further at 150 PPM the water losses are huge.

Plant growth increased 60% since 1900. Because of 110 PPM more CO2.

At 150 PPM plant growth is drastically curtailed. Prior to the current interglacial the CO2 level was less than 180 PPM.

It wouldn't take much to push things over the edge.

The lower the CO2 level the more sensitive things are to disruption. It is estimated the human population dropped to 40-1000 reproductive pairs 70,000 years ago.

That is pretty close to extinction.

 

I can't pretend I know all this Eco stuff, I don't, I did some quick research. It seems about every year Ten thousand species go extinct. How many species are we losing?

My thoughts are this, How much of this extinction is Natural selection, And how much of it is interference of man. I assume species have been going extinct since the beginning of life.

It makes me think about how varied and rich the verity of life on earth may have been hundreds of thousands of years ago. I'm forced to wonder, If so many species are going extinct, And being replaced by Those species that managed to avoid extinction, Is this natural selection? Or is this something like Mans intervention?

 

According to your link it will take between 1000 and 10,000 years to kill off everything on the planet.

But I believe they are just guessing.


Total Number of Species Estimated in the World - Current Results

6.75 million invertebrates (insects and such).

80,000 vertebrates of which about 5,500 are mammals.

At 10,000 per year we would run out of insects in about 675 years.

But a lot of the extinctions are due to invasive species.

Australian feral cats are threatening 27 marsupial species. They are going to cull 2 million of them by dropping poisoned sausages. Marsupials must not like sausage.

 

Poisoned.....sausages......millions of poisoned sausages..,,.

Are supervillains in charge of pest control there?

 

We have a place in the States that serves poison Sausages, They call it Dairy Queen. But No, I kid, Their sausage and biscuits are the best