in Vernor Vinge's novel A Deepness in the Sky the alien planet freezes for part of the year and the intelligent aliens have evolved to survive being frozen and thawed. One group develops technology to say unfrozen while their enemies are frozen and this gives them a huge advantage.
Great book and I highly recommend it. Also has concepts of realistic mind control that is VERY creepy and the ultimate in distributed computing based on smart dust.
Ya' know, Oly was very happy to find his farm was in Iowa, rather than Minnesota. When his friend Sven asked him why, given that taxes were higher in Iowa, Oly replied "Vell, now I don't have to put up vith those lousy Minnesota vinters no more!"
Life in that planet evolved to essentially hibernate during their long winter. Presumably the processes that resulted in the very earliest life forms happened countless times until some surfaced that had that feature.
The habitable zone is defined as the area around a star where liquid water could be found, there is no "our" habitable zone and "their" habitable zone.
Parts of our own Earth aren't in the habitable zone, by that definition. Even here we get big surprises - undersea vents were unexpected oases, microbes miles deep underground, microbes living in boiling water in Yellowstone...
Not all life in the universe may require liquid water, nor require it 24/7. In our own solar system, some planetoids outside our supposed habitable zone likely have some liquid water - Europa and Enceladus, for example.
> Parts of our own Earth aren't in the habitable zone, by that definition.
What parts would that be? Even the polar caps have huge liquid water oceans underneath. Unless you’re talking about the mantle or molten core, there are no uninhabitable areas on earth as per astrobiology (not even miles underground).
> Not all life in the universe may require liquid water, nor require it 24/7.
You might as well be talking about leprechauns and unicorns and Horta. Water is the universal solvent and has at least five unique properties that are as critical to life as carbon’s ability to form four chemical bonds.
You’re correct that moons experiencing tidal heating can contain liquid water, but that’s irrelevant to a planet. The habitable zone is specifically talking about planets (rocky ones at that), not any arbitrary satellite. It’s a term of art in astronomy, not a colloquialism.
> Unless you’re talking about the mantle or molten core, there are no uninhabitable areas on earth as per astrobiology (not even miles underground).
We've found microbes that can survive at 120 Celsius, -25 Celsius, very high and very low pH, large amounts of ionizing radiation, intense pressures, etc. Habitability is a wide range encompasing scenarios not conducive to liquid water.
> Water is the universal solvent and has at least five unique properties that are as critical to life as carbon’s ability to form four chemical bonds.
None of that rules out life on other chemistries. It makes water+carbon-based life the most likely scenario on planets with liquid water, but hardly rules out other potential biologies.
> You’re correct that moons experiencing tidal heating can contain liquid water, but that’s irrelevant to a planet. The habitable zone is specifically talking about planets (rocky ones at that), not any arbitrary satellite.
But we should absolutely be looking at planet-sized moons with potentially habitable conditions, which we believe to be quite common. They are, after all, more common than the single "habitable zone" planet even within our own system.
Is the upshot of this observation supposed to be that PLATO should change its plans and direct its telescope in a different direction because it has more promising places to look than the habitable zones around stars?
If not, and if you can understand why it's prioritizing that, then why do you take this definition of habitability to be tantamount to denying the possibility of discovering other forms of life? For those possibilities to be relevant to a research program, they need to be motivated by something more than "gee, hey, you never know."
So it's not for lack of reflection on those possibilities that we arrive at this operative definition of habitability. There are pertinent reasons for moving forward with this definition that don't amount to denying other boutique possibilities. Construing it that way I think is just an uncharitable interpretation.
It’s not impossible, but we’ve got a ton of evidence why it’s extremely unlikely. It’s a long list including stuff like possible quantum transition states enabling biochemistry, reactivity with oxygen (the third most abundant element), and spectroscopic transparency. It’s an active area of research that keeps coming up with dead ends.
Ammonia and methane are the best candidates but those would only be possible at low temperatures that preclude lots of other reactions.
And none of those smart people have come up with any experimental evidence that it’s actually possible. No equivalent to amino acids or nucleotides or saccharides or… the list goes on.
I’m not talking about SETI, I’m talking about basic chemistry experiments. There are tons of experiments that can spontaneously form amino acids and nucleotides, even way outside the parameters normally considered habitable.
There is tons of concrete evidence, you’re just ignorant of it. Start with Stanley Miller’s seminal 1953 paper “Production of Amino Acids Under Possible Primitive Earth Conditions” and go from there. There’s been a lot of work on the topic since then, several of which have made it to the HN front page.
> Hemoglycin (previously termed hemolithin) is a space polymer that is the first polymer of _amino acids_ found in meteorites.
I’m done, have a great day! (Monomers)
Edit: My apologies for being dismissive. I’d like to get into the specifics of why amino acids (amino and carboxylic groups specifically) are special, and interesting exceptions like hydroxy and alpha-hydroxy acids, but I’ve got to get to work and I could spend an entire year explaining the nuances. The deeper you get into the details, the more the anthropic principle rears its ugly head.
> ammonia-based life form at our stage of exploration is probably gonna scoff at the idea of scaldingly hot liquid water
Ammonia-based life exists within water habitable zones; Mars is within our Sun’s conservative habitable zone [1]. (Also, “ammonia boils at 98°C instead of –33°C” at “60 atm, for example, which is below the pressures available on Jupiter or Venus,” meaning “ammonia-based life need not necessarily be low-temperature” [2].)
One reason to suspect ammonia-based life is rarer than carbon-based life is the universe contains a fifth of the nitrogen that it does carbon [3]. (This is why silicon-based life is also almost written off.)
> The two examples you gave... Include liquid water.
This specific planet spends half its orbit in said zone. Here on Earth, we have creatures like https://en.wikipedia.org/wiki/Mudskipper that can survive severe dry spells, and fish that can happily freeze sold in ice for months.
Europa spends zero time in our solar system's "habitable zone", but because of its conditions, may still possess large amounts of liquid water. It's a perfect example of why the "zone" may be overly narrowly defined, even for Earth-like water-dependent life.
> It is entirely possible there is some other form of life that does not require liquid water, but we have yet to discover it.
And we certainly won't if we only look in Earth-defined "habitable" zones.
You seem to be deliberately trying to pervert the definition of habitable zone.
Just because there are regions on a planet in the habitable zone that contains ice does not mean it is not in the habitable zone. If it were further out beyond the habitable zone, there would be no liquid water at the surface.
To quote my friend Andy Dufresne, "How can you be so obtuse?...Is it deliberate?"
> You seem to be deliberately trying to pervert the definition of habitable zone.
They're fine. Some people here are trying to overextend the definition and it's good to push back.
The habitable zone is about surface water. Pointing out that parts of the earth lack surface water for extended periods is a really good analogy to a planet that drifts in and out of the habitable zone.
Earth is the only environment in which we've found life, so it makes sense to first focus on other Earth-like planets. Your point is not without merit but taken to the extreme it would be like sending exploratory teams to the Mariana Trench to look for un-contacted human tribes.
We have incontrovertible evidence that water + carbon + time sometimes equals life. We have no evidence of any other non-carbon or non-water chemistries resulting in life so why wouldn't we focus on locations potentially rich in water and carbon first?
The first exoplanet detection was in 1992; in my lifetime, "there are no planets outside our solar system" was roughly as supportable as "there is no life outside our solar system" is today.
You seem to be talking past everyone else in this thread because nobody has disputed a single thing you've said however you're ignoring (perhaps unintentionally) the basic statistical reality that if we focus on potentially water- and carbon-rich environments we are as a matter of course more likely to find life sooner.
But the "basic statistical reality" is also "there are a lot more known/accessible planets outside of the zone in which liquid water exists naturally on the surface", which leads to a quantity vs quality consideration for which we don't have enough information to decide right now.
Yes but "we don't have enough to decide" means you have to lean on the single data point you have, not completely ignore it and just try to look everywhere all at once. You have to focus your finite resources and "just pick something" isn't a reasonable path when there's more things to investigate than we could do in 10 lifetimes.
> Or maybe we start with what we know (carbon-based)
But we know more than one thing. One of those things is the Fermi paradox - that the universe should statistically be full of evidence of life, and yet we struggle to find it. That may be evidence we're making the wrong assumptions.
> keep our minds open to other possibilities...
Yes, and I'd argue that means including scenarios like Jupiter's moons in our search. (As a bonus, Jupiter-style planets, being larger and far from the star, are substantially easier to find.)
Like you said, the first exoplanet was detected in your lifetime.
We haven't even had the chance to fail yet, the Fermi paradox is not yet in play when we're considering essentially our first move. To extend an analogy from further up thread, it'd be like looking in the Mariana Trench for un-contacted human tribes after taking a quick glance around the neighborhood and deciding there's nothing else to be found anywhere else.
There's a meaningful operative definition and you're muddying the waters over that definition on the grounds that, hey, who knows, maybe it's different somewhere in some way.
I just think you're confused if you think that observing a specific definition of habitable zone is tantamount to a specific denial of that possibility.
I'm not confused by its definition, I just dislike the use of the term. It leads to significant confusion in laypeople - "they found a habitable planet!" is something I've heard breathlessly repeated multiple times, and "but Earth is so perfectly placed, it can't be by chance!" used as an argument for creationism.
Regardless of the official definition, the word “habitable” is highly subjective. Extremophiles like tardigrades can survive being frozen and/or completely dehydrated. A planet with an eccentric orbit like this one could hypothetically support species capable of entering some form of extreme hibernation during part of their year.
And that's fine, but when communicating outside the speciality, I'd really like to see some other term used.
https://www.cjonline.com/story/news/politics/government/2025... for example says "Kansas tuberculosis outbreak is now America's largest in recorded history", where "recorded history" is apparently the CDC's "term of art" for "since 1950", which isn't what a layperson hears.
The IAC is communicating outside the speciality here, via a press release.
That's why the article's breadcrumbs say "Home > Outreach > News".
We saw the same issue during COVID - scientists talking to the general public often talk like scientists instead of science communicators, and that causes people to misunderstand. Fauci's "no evidence" (yet) masking prevents disease incorrectly becomes evidence masking can't prevent disease.
Not many uninterested laypeople are going to be browsing the IAC website for astrophysics news. People that are interested should probably familiarize themselves with the terminology commonly used in astrophysics.
Once it makes its way to PBS Space Time, sure, maybe you avoid terms of art. Or explain the particular definition when it is first introduced.
That's just my opinion anyways. I always try to familiarize myself with the common terms of art when learning about a new discipline.
> Not many uninterested laypeople are going to be browsing the IAC website for astrophysics news.
But they will get linked to it, or read articles by reporters using it as a source without enough domain knowledge to make the distinction. I, after all, didn't seek this out - it just popped up on the HN home page.
> What seems weird to me is to be interested in a discipline, seek out news and conversation about it (from university press releases!) but then reject and/or argue about any terms of art that are established within that discipline.
I think science communication, post-COVID, needs to take a serious look at how to better explain things to the public. "Habitable zone" is simply one example of it.
I edited part of that out, because I actually do broadly agree with you regarding science communication, and realized my comment was a bit stronger than I intended. Looks like you were quick on the quote!
However, I think there's some serious slack to cut when you're viewing an article on the Institute of Astrophysics website, compared to reading Fox/CBS/whatever.
Edit: In my re-reading of the article, I see they define it! I'm no longer sure what all this back and forth is even about. "This orbit places it within the habitable zone of the system, _meaning it is at the right distance from its star to sustain liquid water on its surface_" Do you want them to not use the term even when they define the term?
> Do you want them to not use the term even when they define the term?
Yes, I do. I think it's a needlessly confusing term to use in stuff intended for public consumption.
For a similar example of the issue, I often get radiology reports in my healthcare provider's portal. My dad is a radiologist and they're still quite scary/bewildering to read - they frequently use various terms of art for "looks fine and normal" that sound terrifying.
That was all fine when the intended audience was other doctors, but these days I can pull them up myself. I at least know enough to not freak out and ask my dad; many don't.
I don't want to see NBC/BBC/NYT articles using the term, and that means being careful with the sources from which they receive their info.
While it's possible for conditions for life to emerge or sustain itself to be present beyond the habitable zone (e.g. there's likely a subsurface ocean orbiting the farthest plant from the Sun on Triton), afawk it is more probable that life forms in the habitable zone. That is the only one we have a data point for.
The terminology was probably chosen specifically to be somewhat clickbait, so it's probably not worth picking apart the words "habitable zone".
The core idea really boils (heh) down to water, _i.e._ the "universal solvent". You can certainly argue that liquid water may not be necessary for life, but it's hard to argue that water's presence isn't a decent prior for potential life.
But directly detecting liquid water in extrasolar planets is _hard_. So we do the next best thing and try to use whatever indirect signals we got. We know that liquid water can only exist within some range of temperatures and pressures. So let's just start with temperature.
What things can affect the surface temperature of a planet? Amount of energy received from the parent star (i.e. stellar irradiance), geothermal heating, tidal forces between a moon and planet, and probably many others. Stellar energy stands out as being the biggest contributor of energy and, fortunately, the easiest one to measure.
Of course, you could have localized sources of favorable conditions, like thermal vents or whatever, but those kinds of things are _way_ beyond our ability to detect with current tech.
So, we've narrowed down our focus to _one big contributing factor for potential life_, the amount of energy received from a planet's host star. But how can we relate energy to temperature? This is effectively where all the physics and astronomy come in via thermodynamics, orbital mechanics, and stellar physics.
Suffice it to say that all the effects combine to give a range of possible orbital radii and planet sizes where liquid water has a good chance of existing on the planteary surface.
This range of radii and planet sizes is the concept that matters. The name for this idea is "habitable zone", which suggests why we might care, compared to the more precise "orbital and planetary mass parameters favorable to liquid water formation at average planetary surface".
This kind of resource variability seems likely to favor the development of intelligence, so there’s that.
But I m sure we will find that the planet has issues that make complex life unlikely, just on a statistical basis.
Simple life seems increasingly likely to propagate through panspermia, based on what we find deep inside the crust of our planet. Life forms that feed off of radioactive decay especially seem promising for panspermia.
I wouldn’t be surprised at all if we discovered that for habitable zone, earth-like planets , the presence of simple life forms deep inside the crust turns out to be the rule rather than the exception, at least in our corner of the galaxy.
> Its distance from its star changes significantly, causing the planet to move from the outer edge of the habitable zone to the inner edge throughout its year
