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Comment by dylan604 | Hacker News Reader

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?"

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> 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.

> You seem to be deliberately trying to pervert the definition of habitable zone.

No, I'm saying an Earth-life centric metric is a bit of an odd choice when evaluating extrasolar planets.

It's like an African elephant declaring Norway uninhabitable.

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.

Here on Earth, we can barely decide if viruses are life or not, and discover new things within our own bodies pretty regularly, despite... a lot of direct access to them. (Example: https://www.science.org/content/article/it-s-insane-new-viru...)

We should be casting a pretty wide net.

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.

The correct scientific approach to a sample size of one tends to be "not enough information to make a decision".

Lets start our search for helium-based life forms immediately!

Or maybe we start with what we know (carbon-based), and keep our minds open to other possibilities. Like we do now.

> 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.

Look up "informative vs uninformative prior".

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.

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