*My* theory on alien life and our planets place in the galaxy

[k9bfriender]

@dtilque

The Earth is way bigger than it needs to be to hold an atmosphere. In fact it could hold one 100 times as dense. Venus is somewhat smaller than Earth, yet its atmosphere is 90 times greater pressure than Earth’s.

And Mars isn’t. I’m not talking fine tuning to a fraction of a percent, I’m talking being in the right order of magnitude.

Venus is 82% the mass of Earth. The reason that its atmosphere is so dense is because it is made of carbon dioxide. Nitrogen and Oxygen have a 13% and 17% greater molecular speed, respectively, and water is almost 70% higher. Carbon dioxide is much easier to hold on to.

What size is required is a good question. Obviously Mars is way too small, at about 10% of Earth’s mass. We don’t have enough samples to say exactly how big a planet needs to be to hold onto an atmosphere and magnetic field.

And, being bigger poses its own problems. Even if nothing else changed, it would make it harder to get into space.

@dtilque

AFAIK, the moon isn’t required for tectonic action. You have a cite that says it is?

I didn’t say that it was required for tectonic action, I said it helps.

Anyway:
https://www.sciencedirect.com/science/article/pii/S1674987117302037

Since the solid Earth tide oscillation is longer in one side relative to the other due to the contemporaneous Moon’s revolution, we demonstrate that a non-linear rheological behavior is expected in the lithosphere mantle interplay. This may provide a sort of ratchet favoring lowering of the LVZ viscosity under shear, allowing decoupling in the LVZ and triggering the westerly motion of the lithosphere relative to the mantle.

Can the position of the moon or the planets affect seismicity? Are there more...

Earth tides (Earth’s surface going up and down by a couple of centimeters) and especially ocean tides (surface of the ocean going up and down by a meter or more) raise and lower the confining pressure on shallow, dipping faults near continental edges and in subduction zones.

When the confining pressure is lessened, the faults are unclamped and more likely to slip. The increased probability is a factor of ~3 during high tides.

A quora answer, FWTW.

How does the moon affect plate tectonics?

Tide´s effect is not just moving the sea water, it also deformates the lithosphere hold by plates (monitoring fluid pressure in closed reservoirs few tenhs of PSI can be detected in coincidence with tides). Crust deformation plays a role changing friction from static to dynamic allowing faster displacements as the interplates tension required are lower.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.596.4592&rep=rep1&type=pdf

The detection of tidally-triggered events suggests that tidal
stresses, which are typically smaller than 0.1–1% of tectonic stress
magnitudes, are sufficient to trigger up to about 0.2–0.3% of all the
earthquakes of the NEIC database. However as mentioned above, this
global earthquake catalogue is not complete for small magnitude
events (less than 4.0) that we have shown to be more easily triggered
by tides.

Is the science settled? Of course not, it may never be. But, the consensus that I have seen when I watch astronomers and geologists have discussions is that the moon does help the lithosphere stay broken up. The tidal flexing makes the plates more flexible and able to slide over and below eachother. It also may relieve stress through lots of little tiny earthquakes, preventing build ups for big ones.

If there was no moon, we’d still have a liquid core and mantle, but we’d most likely have big volcanoes that grow on top of hot spots, like Venus and Mars do.

We’d have a very different looking landscape without a moon.

Also, keep in mind that the moon used to be much closer, and the Earth spun much faster, so it had a much greater effect on both the land and the sea than it does now.

And like I said, you misread what you quoted, when you implied that I said it was required for tectonic action, rather than helping it.

You also did not, I see, object to my point that the moon causes tides. there is quite a bit of educated speculation that tidal pools had quite a bit to do with the formation of early life. And it has undoubtedly had even more to do with the continued evolution of later forms of life.

@dtilque

My understanding is that Jupiter is not especially protective of the inner planets. It may snatch up some rocks, but it also redirects rocks from the outer Solar System into the inner, thus setting up collisions that wouldn’t occur otherwise.

Orbital mechanics are complex, and there are numerous theories as to Jupiter’s role in the formation of the solar system.

I see one guy, Kevin Grazier, that ran some simulations that got a bunch of headlines. Simulations over such periods of time are inherently unpredictable. Even in the simulations, it’s not as if it is snatching rocks up from the outer solar system, it is that when rocks come from the outer solar system, they may interact with Jupiter and Saturn in such a way that they stay in the inner solar system. The reverse is also true, it can eject a rock out to the kuiper belt. My understanding is that the latter happens more than the former, and obviously anything that actually hits it is out of play forever. For instance, Comet Shoemaker Levy no longer poses a threat to Earth.

[filmore]

From what I understand, the benefit of the moon is that it created tidal pools which encouraged the evolution of land-based animals. Sea animals would get trapped in the small pools and would gradually evolve to breathe air and walk on land. Land-based animals could have still evolved without the moon and the tidal pools, but there would be much less evolutionary pressure to move in that direction and less land-based diversity.

[Ashtura]

Even intelligent alien life might have environmental disadvantages that keep them from getting too technically advanced, or slow it down, a lot.

For example, say you have an intelligent aquatic alien. We have technologies that simply would be very difficult to pull off underwater. Wireless technologies, for example. Heck, using electricity at all would be challenging. Not impossible, but we’d definitely have a leg up. They’d have fancy submarine travel probably, but flight for them would be a pain in the ass, and space travel even more so.

[dtilque]

Awesome reply, k9b. Haven’t had a chance to review all the cites, but they look interesting.

[Folly]

My hypothesis is that there are a lot of slimeball Earths out there and that the jump to more complex life is really, really difficult and rare.

[Mijin]

The funny thing about Fermi’s paradox is everyone accuses everyone else of making assumptions, while not recognizing their own. The majority of posts seem to be “Why does everyone assume X, when ISTM the answer is obviously Y”.

Let’s just all agree that virtually all these ideas, both X and Y, are pure conjecture.

That’s the point of the paradox: lots of explanations might seem plausible to us, but we don’t know.

What is less conjecture however, is the number of planets that likely exist, and the number of planets in the habitable zone, because here we at least have some empirical data to go on.
It’s a little disheartening to find in this thread certain posters again asserting, incorrectly, that the data suggests such planets are rare.
Because, based on the limited situations in which we would be able to detect a planet as small as the earth, as far away as 1 AU, and based on the number of planets we have detected at these limits of our ability to detect, we can conclude that small rocky worlds with temperatures in the range for liquid water, are likely common.
Yes, this doesn’t mean all, or even any, of them, are actually suitable for life, but it’s certainly not support for the proposition that suitable planets are uncommon.

[eburacum_45]

I have not said that these planets are rare. I have said, correctly, that no planet so far detected is a good match for Earth. Do you deny this?

[eburacum_45]

Here’s the Earth Similarity Index from 2020, with a notable ‘desert’ around Earth.

PHL @ UPR Arecibo - Earth Similarity Index (ESI)

Sure, there are probably plenty of good matches out there, but they aren’t yet visible. I admit, however, that the Earth of 2 billion years ago would not be a very good match for the Earth of today, and the Earth of 2 billion years from now would be even worse.

[Mijin]

@eburacum_45

I have not said that these planets are rare

And I have not said that you have. I was alluding to some of the posts earlier in this thread.

@eburacum_45

no planet so far detected is a good match for Earth

This depends on how similar a planet needs to be to be considered a good match. We’ll never find a planet identical to earth in all measurable properties.
So it’s arbitary, but sure, I would not contest the statement that we have not found an earth sister planet yet.

But nor can we detect such planets well. And we don’t know if being earthlike is actually a requirement, vs just being able to have liquid water on the surface say. So in my view, it’s not a useful framing of the issue.

[msmith537]

I was going to start a separate thread on the question, but this seems as good a place to ask it.

In the film Ad Astra, much of the plot revolves around the “Lima Project”, an initiative to definitively determine if there is intelligent life elsewhere (it’s not clear if “elsewhere” is the universe, the galaxy, or just our local stellar neighborhood.)

My question is this. To what extent could we run a “Lima Project” to definitively rule out intelligent life in other solar systems (i.e. detecting signals or viewing constructs that would be impossible to find in nature). I imagine it’s a fairly complex problem. We would be unlikely to ever “see” cities or megastructures smaller than a Dyson sphere outside our solar system. Encrypted signals using unknown protocols might be indistinguishable from background noise.

[Cheesesteak]

@msmith537

To what extent could we run a “Lima Project” to definitively rule out intelligent life in other solar systems

We would have to basically send a spy satellite to orbit every planet in every solar system in the galaxy. Humans would have been utterly undetectable 200 years ago without that level of scrutiny, so I’m using that as the baseline. Ruling out intelligent life is proving a negative, which is extremely difficult to do conclusively. Even if we did that, all we did was prove a certain level of technology was undetected in 100 billion solar systems.

[k9bfriender]

It depends on what you define as “intelligent”.

If a planet has the equivalent to whales and dolphins and they are intelligent, then you are going to have to actually go to the planet and swim in its oceans to determine that. We are on our planet right now, swimming with them, and we aren’t really sure one way or the other.

If you are talking land based tool users, then that’s a bit easier. There will be signs on the surface of artificial construction. With good enough telescopes, such things could be seen from our solar system, but we are talking about space based telescopes at least dozens, if not hundreds of miles in diameter. And that’s for the closer ones.

Technological civilizations may be easier to see. We don’t know of any natural way for CFC’s to form, so if we see those in an alien world’s atmosphere, then there’s a decent chance that there is technology there, or that there is some natural way for CFC’s to form that we didn’t think of.

Obviously, picking up a coherent radio signal from another world is the gold standard of SETI. If we start picking up the “I love Leelo” show, then that’s a pretty concrete indicator of intelligent life out there. Same as if we find a directed transmission sent to greet other intelligent life.

The more encrypted or compressed a signal is, the more random it is, but that doesn’t mean that it is indistinguishable from background noise, as it is still a radio signal. If we detect radio transmissions coming from a particular star that are separated into regular bands, then even if we cannot decode them, it would be pretty good evidence that they were artificially generated. If you look at our AM or FM transmissions, you will see that there are gaps between the different frequencies. Gaps that have no real reason to be there, other than because of arbitrary rules that we came up with to make tuning our devices to those frequencies easier.

Part of the whole point of the Fermi “paradox” is that we shouldn’t have to look that hard to find alien life, it should be obvious and probably already here. Not as visitors who stop by for tea, but as colonists that set up shop millions of years ago.

I have some plans for redecorating the neighborhood, if we continue to advance as a technological species, and those decorations would be very visible from across the galaxy, even across the visible universe. The assumption is, if alien intelligence is common, then at least one other alien species out there would have the same drives as we do, and would have done millions of years ago what Musk and Bezos are planning on doing.

[John_DiFool]

Studying changes in the atmosphere of the exoplanet in question remain your best bet, via spectrography or such, tho of course the detection distance would be relatively limited. Are they any gases or pollutants which are mostly or exclusively of non-natural origin?

[begbert2]

@k9bfriender

Part of the whole point of the Fermi “paradox” is that we shouldn’t have to look that hard to find alien life, it should be obvious and probably already here. Not as visitors who stop by for tea, but as colonists that set up shop millions of years ago.

AKA octopi

[eburacum_45]

@John_DiFool

Are there any gases or pollutants which are mostly or exclusively of non-natural origin?

I suspect not. Even chlorofluorocarbons might be generated naturally by a biosphere that is sufficiently different from our own. Biological processes could conceivably refine and utilise halogens, either as an unwanted waste product or as an essential part of their metabolism.

Weird molecules might be suggestive of the presence of a civilisation, but they could also be biomarkers from biochemical processes we don’t recognise yet. Always beware of false positives.

[k9bfriender]

True, as I said upthread CFC’s could be an indication of technological life, or they could be an indication of a natural way of making them that we don’t know yet.

Either way, if we detect them in the atmosphere of a planet, it certainly bears some intense study.

Other than that, changes over time may give us some ideas. If we see a planet, over the course of a few decades, rapidly change from a freezing airless ball to something that could sustain liquid water at the surface, then that is either an indication of terraforming, or another biological process that we do not understand yet.