[shireboy]

This could mean in the Drake equation ne -number of planets capable of life- is very small. A planet has to be hit with a comet big enough to deliver a large amount of water but not so big or fast to destroy it. And be in the Goldilocks zone of the star. Also the mass of the planet would play a part - gravity of more massive ones would be more likely to capture a comet. But again, too massive and I could see that hampering life.

[JamesLeonis]

The Drake Equation is filled with assumptions, like life must appear on a planet in the Goldilocks zone of a star. The whole equation has only one datapoint to extrapolate from. Tweak the equation's parameters and it will predict universes that only have one civilization per galaxy or worse! We have no way of knowing what those parameters are because we haven't seen other examples.

A major reason we are interested in Europa is because it might have underground oceans. Hypothetically, through tidal forces with Jupiter, the moon's core is hot enough to create oceans under the ice crust. Combined with hydrothermal vents you have the possibility for deep sea life similar to our own deep oceans. The Drake Equation does not predict this possibility.

[mr_mitm]

The Goldilocks zone doesn't enter the Drake equation at all.

As a reminder, this is the equation: https://en.wikipedia.org/wiki/Drake_equation#Equation

It makes very few assumptions.

[corimaith]

Even if you only had a handful of civilizations, the sheer time that has passed and size of the universe should mean that life should still be alot more apparent.

With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?

Another point I feel is that proliferation of life should be an self-reinforcing affair, for intelligent life even more so. A spacefaring nation may terraform or just seed planets, and these in time will replicate similar behaviors. At a certain point, a galaxy teeming with life should be very hard to reverse given all the activity. A life itself isn't necessarily evolved from biology, AI machine lifeforms should also well suited to proliferate, yet we don't see them anyways.

[raverbashing]

Yup

The fundamental problem with the Drake equation is that it's frequentist, not Bayesian

Hence why you get too high sensitivity to parameters you have no way of having an estimate with a small margin of error

We "don't care" about how many civilisations are out there, we care to the point where we can interact with them.

As mentioned, it has several assumptions. "Rate of birth of sun like stars" means nothing. You can "always" have an exception for life that will throw the data off: "star too bright but with a hot Jupiter tidally locked in front of your moon, shielding it" etc

[adastra22]

FYI just about every outer solar system moon or planetoid has a liquid ocean somewhere underneath. Europa is neither exceptional or even that interesting anymore.

[bethekidyouwant]

Not really there’s always gonna be water comets in the frost zone.

[andrewflnr]

I don't see any reason to believe that giant impact is the only way to get life-supporting amounts of water. We know Mars had liquid water. We know Titan has lots of ice. We're pretty sure Venus at least had noticeable amounts of water. Did all of these come from Theia-type impacts? I don't think we have any evidence of that.

[II2II]

Multiple impacts is the standard hypothesis for a source of Earth's water. If I recall correctly, outgassing from volcanos is another source.

Keep in mind, the solar system formed from a relatively homogenous nebula. It was the formation of the sun that forced lighter elements to migrate outwards, and that only happens if the lighter elements aren't already part of a larger object. There isn't much of a difference between a 10 km chunk of ice and a 10 km chunk of iron gravitationally speaking. Bouancy doesn't play a role here, so density doesn't matter. Outgassing does matter, but that is a slow process for large object, like the Earth, or for smaller objects on Earth crossing orbits that don't get too close to the sun.

It's also worth considering that each planet's situation is unique. There is much more water ice on the moons of the outer solar system because there was more water at the time of formation and the lower temperatures mean the water that was there stayed there. As for Mars, even though it is colder than the Earth, it is much less massive. As such, its atmosphere bleeds away lighter molecules (never mind lighter elements).

[sesm]

Yep, mega-impact is a classic example of an ad-hoc hypothesis. For example, Moon formation is much better explained by multi-impact hypothesis, which also requires less assumptions.

[nebula8804]

I recently became addicted to the SpaceSimsx and SimulaVerse. My takeaway is that so many just slight deviations can extinguish life on earth. I used to think of possibility of life in other worlds just in the lens of statistics. There are so many combinations and possibilities that it seems inevitable. But seeing just how perfectly aligned our solar system is makes me really reduce the probable number of chances of other habitable scenarios in my mind.

These channels helped me realize just how important all the planets in the solar system are to our continued existence. Its as if we have an entire family thats just perfect to make our existence possible. An entire family each one quietly doing their part without fanfare or credit.

What if we had 2 moons with half the mass?: Destruction [0]: https://www.youtube.com/shorts/v3xxaTkKGTQ

What if we moved Earth 5% further from the Sun?: Destruction [1]: https://www.youtube.com/shorts/g-na5x0Kldk

What if we dimmed the Sun by 1%: Destruction [2]: https://www.youtube.com/shorts/Cc3DRRJxhB8

What If We Delete the Biggest Planet from Our Solar System?: Destruction [3]: https://www.youtube.com/watch?v=kHJpIWoksKw

What If We Delete All Gas Giants Except Jupiter?: You guessed it...Destruction [4]: https://www.youtube.com/watch?v=Eg9fPNg00EE

[WalterBright]

> perfectly aligned

No matter what the circumstances, live will evolve to perfectly match the conditions it is under. There are many species so perfectly adapted to their ecological niche, they are in great danger of extinction. Like peacocks, who are stuck in a local optimum with no way out.

[javier2]

Well, just keep in mind that its not a "perfect alignment" as this seems to prescribe some kind of intent. It's more a set of requirements that allowed life to not be extinguished so easily. We could never exist in a place where this didn't happen like this, so obviously we have to be here and not some place ealse. So its more that out of the 1 places we have seen that was made like this, we at least know life happened there.

[snorbleck]

Could a tardigrade withstand these scenarios? If the answer to any of those is yes, could we then say that even with the parameters skewed a bit, there is a chance life exists elsewhere, and under completely different and extreme or (not "normal") conditions? Is the tardigrade here as a "clue" to tell us that life could form potentially anywhere?

[HarHarVeryFunny]

The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time.

e.g. Say chance of a random planet ever being hit by a water-carrying comet is one in a billion, then with 100B - 1T planets in the milky way it'd happen here 100-1000 times. If chances are only one in a trillion, and we're the one in the milky way, then there are still another 100B - 1T galaxies out there and therefore a similar number of such events.

[tshaddox]

> The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time.

But numbers can go arbitrarily low.

[rdtsc]

Just as easily as we can multiply planets times systems times galaxies times cluster groups we can multiply multiple small probabilities of each chemical being present at the right time and right type, temperature ranges, gravity ranges, etc

[mattmaroon]

If the numbers you propose turn out to be accurate then the odds of there being other life are near zero because even 1/1000 planets are not habitable likely.

[pavlov]

Do other galaxies matter here? A civilization would need to be incredibly powerful to be detectable from another galaxy.

[OgsyedIE]

Unless collisions like the article suggests are a statistical inevitability, that is.

[dotancohen]

Hydrogen is the most common element in the universe. So long as you have elemental oxygen, it will react with things and hydrogen is the thing it will react with the most. So having water is almost a given for any Star system. Additionally, protoplanet and cometary collisions are in fact statistically inevitable. The real question is if water can be delivered at a point after enough gravity has amassed to ensure the water stays there.

[jug]

Right, that's the sticky point? The likelihood of a planet in the Goldilocks zone to be too hot in the early stage of stabilizing its chemistry that it requires seeding with "post-formation" chemistry? Is that likelihood close to 100%, or maybe not even near and we were just set up for a funny cosmic event.

[frankohn]

I agree. In addition to the chemical elements like water, as mentioned in the article, the impact with Theia also enabled strong magmatic activity at the core of the planet, and that was a critical element as well to sustain life.

Probably the strong magnetic activity of the Earth's core was key to maintaining the atmosphere, but also, the magmatic heat contributed to keeping the planet at a good temperature to support life when a young Sun provided significantly less radiation.

All these elements may suggest that the collision is needed to satisfy the very strict requirements about where the planet is located and about the size and composition of the colliding planet. This makes the probability for life-sustaining planets in the Drake equation extremely low.

As an indirect proof of the tightness of the condition is the fact that the Earth in its history had periods of climate extremes hostile to life, like the Snowball Earth when the planet was completely covered by ice and snow, or at the opposite extreme, the very hot periods when the greenhouse effect was dominating the climate.

[gtowey]

If Mars contained significant amounts of water in its past as we suspect, that would mean we have n=2 just in our own solar system.

[GWBullshit]

Speaking of Drake equations, you should (1) see the other comment here with this account name (2) check out the top Pirate Bay rip of Dark City (which predated that other movie) and turn on the English subtitles and count the number of times the characters look at or make gestures pointing to certain alignments of the text in the subtitles and, if you're true "hackers", try to figure out the encrypted messages in the text alignments that the characters are looking at/pointing to at key moments – and then when/if you figure out what the encrypted messages mean, try to figure out how the director worked together backwards so that they could have a script that aligns a certain way using subtitles and then make the scenes so that the actors are looking/pointing to key spots at just the right time.

If you appreciate technical things, you'd be in for a treat.

[Animats]

Right. It's discouraging. We now know that many stars have planets, and some of them are even in the Goldilocks zone. But if it takes a planetary collision to get water... And only one planetary collision, because each one wipes out essentially all life.

Look at the rest of the solar system. Mars - almost no water. Luna - almost no water. Venus, maybe water[1], but as steam. Too close to the sun and too hot.

[1] https://phys.org/news/2025-10-venus-clouds-reanalyzed.html

[Kerrick]

I find it incredibly encouraging. I fear aliens existing in sufficient enough quantity to find us more than I fear Earth being the only host to intelligent life until we escape it.

[WalterBright]

Especially in the context of this, I am baffled by people who go to great lengths to prevent life from Earth arriving on other solar system bodies. Such as all the efforts to sterilize the probes.

[dleeftink]

Historically to prevent pre-contamination and erroneous biosignature readings. This may ease once we have some solid pointers or confidence there may be none (caution is likely warranted due to the gravity of such a discovery).

[quotemstr]

Planetary collisions happen all the time. All of Mercury, Venus, Earth, and Mars in our solar system had them. We can see their signatures in other solar systems too: see https://en.wikipedia.org/wiki/List_of_extrasolar_planetary_c...

Whatever the great filter is, it's not planetary-scale collisions during the accretion phase of solar system formation.

[mr_toad]

A couple of dozen collisions out of 6000+ known exoplanets. Not exactly common, but not freakishly rare either.

[shaky-carrousel]

Not so much, because both Venus and Mars also have water. So whatever gave Earth water is common enough to also give it to the other inner planets.

[kulahan]

Don’t forget this can only happen once, really. You need it to be such a rare event that it doesn’t keep sanitizing the planet with repeated impacts, but one really perfect strike will bring what you need and allow life to form.

The number of instances where this (something unreasonably unlikely) happened in our cosmological history is kinda surprisingly high. I’m absolutely convinced there’s no advanced life (and CERTAINLY no technological civilizations) outside of earth.

One other example: we gained most of our adaptability, curiosity, and problem solving skills as very tiny mammals while dinos ruled the earth. The only way we ever took over the planet was thanks to an asteroid wiping out all those huge creatures. Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.

Our intelligence exploded largely because that extinction event removed almost all major predators, turning earth into a giant survival puzzle sandbox for mammals to grow in.

Edit: our brains only grew big because it was the best means of survival - they’re crazy expensive, so without this “sandbox puzzle” effect, we probably never would’ve grown them.

[mr_toad]

> Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.

Maybe it was just being small, puny, and having a tendency to cower in burrows was what saved us. Our ancestors may not have been much smarter than squirrels, and squirrels aren’t very bright.

Hominids brains didn’t get big until long, long after the KT extinction. A Tigers brain is not that much smaller than that of an an Australopithecus.

[tastyfreeze]

Earth has been struck by large comets many times killing the majority of life on the planet each time. In an early solar system it would be more frequent. Once a comet impacts there is one less comet out there. The solar system cleans up over time making impacts less likely over time.

[nntwozz]

This also points to panspermia.

"The hypothesis that life, in the form of “seeds” or spores, is distributed throughout the universe, traveling between planets, moons, and other bodies via space dust, asteroids, comets, and possibly even spacecraft."

I want to think that the water contained life and not the barren earth.

[jcims]

Bit of a nit but the Drake equation is intended 'to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy' (from the Wikipedia entry for it). Nice thing is that you can drop a few terms to get to origin of life.

[adverbly]

No kidding... This would probably resolve the Fermi paradox if proven true...

[29athrowaway]

Mars is technically in the goldilocks zone of the solar system... but water on Mars boils at 0C or 32F due to low atmospheric pressure, which really sucks.

[xbmcuser]

Your assumption we need water for life to exist is in my opinion wrong. We only know Earth so assume that is what is needed for life to exist.

[joshuahedlund]

There is a hard limit on the number of atomic elements, and an even smaller limit on the number of soluble compounds that facilitate chemical reactions, and water is demonstrably both the best and the most common in the universe.

So while it may be possible for life to exist without water, any alternatives should be reasonably expected to be even more rare than water-based life

[caymanjim]

There's a reason life is carbon-based, and it's not random. It's the only element that works, due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable. There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy. And no other elements have any hope. If you have carbon-based life, you need water as solvent and medium.

It's a pretty safe assumption that all life requires water.

[modius2025]

1. xbmcuser’s point: They challenge the anthropocentric (Earth-centric) assumption — “we only know life as we know it.” Philosophically valid, but scientifically weak without proposing a viable alternative chemistry.

2. joshuahedlund’s reply: Grounds the argument in chemistry and probability.

There are only ~90 stable elements → a finite combinatorial chemistry space.

Among possible solvents, water is the most abundant and chemically versatile (dipolar, wide liquid range, high heat capacity, good at dissolving ions and organics). → So even if other solvents can work (like ammonia, methane, formamide), the odds heavily favor water-based life.

3. caymanjim’s addition: Brings in carbon’s unique valence behavior:

4 valence electrons → can form stable, complex chains and rings.

Bonds are strong but not too strong → dynamic yet stable biochemistry.

Silicon (next best candidate) forms brittle, static lattices and poorly soluble oxides → bad for metabolism. → Therefore: if life is carbon-based, water is the only sensible solvent.

[yosefk]

What's the chemistry of life without water? Do you refer to the promising Russian studies of life sustained by alcohol?

[warent]

You’re getting a lot of negative feedback for whatever reason, but you’re absolutely right.

I for one remember reading about possible silicon/methane based life, etc. Actually, here’s a whole wikipedia article on what you’re talking about.

https://en.m.wikipedia.org/wiki/Hypothetical_types_of_bioche...

Perhaps HN folks will lose your scent now and direct their snark there

[mensetmanusman]

The Drake equation is whatever math leads to Earth being the only planet with intelligent matter out of infinity planets.

[renshijian]

A brilliant summary! You've deepened the question from "Does a habitable planet exist?" to "Does a planet successfully complete the complex dynamics of life's origin?" The habitable zone is merely the ticket, while the conditions you mention are the truly demanding filters. Considering this, the probability of our existence truly seems miraculous

[ctrlp]

The likelihood of those criteria might be vastly different in a younger universe than in this one, no?