I think the proper term is circumstellar habitable zone. If there is other life out there, why are we assuming that it’ll have the same basic needs as our animals? The universe is seemingly infinite, and there’s endless possibilities of what’s out there, so why do we only consider planets that are the ‘perfect’ distance away from their star?
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**TLDR: There’s not enough time and resources to check all the planets, so we check the ones most likely to have (our type of) life because (1) we know life can exist there AND (2) we’ll recognize that life when we see it.**
>why do we only consider planets that are the ‘perfect’ distance away from their star?
Two main factors:
1. Because there’s only enough telescope time to consider a tiny subset of known planets, so we prioritize looking at the ones where we **know** life could exist (because they have conditions like Earth), over ones where maybe some other form of life exists, or maybe not.
2. Because for any life that isn’t like ours, how would we know what to look for? Or rather, **how would we even recognize sings of that life when we saw it**? Let’s say there’s silicon-based life out there that breathes out silicon dioxide instead of Earth’s carbon-based life that breathes out carbon dioxide. But you know what else has silicon dioxide? Rocks, glass, and sand. So if we saw a far off planet with a bunch of silicon dioxide, we’d just assume it’s a rocky barren planet – and completely miss discovering the RockBeings.
It boils down to “you need to know what you’re looking for”. We know what all the signs of life on Earth are, and by definition have no idea what other types of life would be made of, because we’ve never seen them before, so we couldn’t recognize them as “signs of life” even if we *did* detect them.
Like, when you analyze a planet, best-case the spectrometer basically says “here’s a list of 118 chemicals detected in the air of that planet”. From that list, how do you know if there’s life? Well, pretty much all you can do is compare the list to chemicals we know are made/used by living thing on Earth. There may well be other life forms making other chemicals on that list, and no one is saying there isn’t! It’s just less likely to be found by us, so we prioritize elsewhere.
Maybe one day we’ll be good at looking enough to look everywhere, and then we will!
For now, it’s *really really* hard to look, and we already know a lot about one kind of life: the kind we have here on Earth.
To hammer this home, just a couple years ago there was excitement around finding life markers on Venus. Venus. The planet right next door. We hadn’t been able to look at that one closely enough to rule out life.
In a nutshell, for every trillion planets out there we only have the time and skill to look at five of them, and the only way we know how to look is for familiar stuff anyways (e.g. radio signals). We’re shooting our best shot, but maybe in a thousand years we’ll be able to look much more carefully.
It’s just safe to assume that what worked for us would work for others
If a planet has similar conditions to our own then we could expect organisms similar to ours to exist there, with slight variation of course
Life can be literally anywhere. But, the higher the chance of liquid water, the higher the chances of life. It’s a number game. Look at 1000 goldilocks planets, or a few hundred thousand plutos
Stand too close to the camp fire(Sun), you get burned.
Stand too far away from the camp fire, you are freezing.
Stand Juusstt close enough to the campfire in the goldilocks zone, and you feel warm and cozy for life.
Because we’re looking for life as we know it. We’re not looking for other forms of life because we don’t know what to look for.
The main assumption about life we are making is that it many chemical reactions work best at specific temperature; and so having a material that is thermally stable (it doesn’t change temperature easily) that can also allow things to move is useful.
If that assumption holds, there’s only two options: water and ammonia. Both have remarkably high “specific heats” (measure of how much energy it takes to warm/cool them) and dissolve a wide range of other chemicals when liquid. Therefore, if that assumption holds, life can only exist in areas where you can find liquid water or liquid ammonia.
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Could life exist somewhere else? Yes. But we have no idea how they would look or what to look for. We know exactly what to look for for water-based life; and can make reasonable guesses for ammonia-based life.
How do we determine what is life? The classic examples are a mule (sterile and does not normally reproduce), a virus, a fire, and a radium clock. Sci-fi is full of examples where life does not meet our preconceived notions, and since we only know about life on earth, everything else is speculation. We look in the Goldilocks zones because that’s what we are familiar understanding. It doesn’t mean we are right, there could be living ion clouds in Jupiter or living rocks here on earth, but it is our best shot at the moment.
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