Why do we look for life on ‘goldilocks’ planets?

Question

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?

In: 46

Answer 1

**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.