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Comment by BinaryAsteroid | Hacker News Reader

The timing of the delivery is what's important here. These building blocks, organic matter, and water would have been depleted in the proto-Earth due to Solar irradiation. There needs to be some mechanism that delivers these ingredients from the outer Solar System. Bombardment by smaller rocks makes the most sense, and was likely triggered by the migration of Giant Planets, leading to a period of heavy bombardment (on a bare Earth -- no oceans, no volcanoes).. https://en.wikipedia.org/wiki/Nice_model

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Huh? Those smaller rocks would be even more irradiated, as they have no atmosphere?

They’d also have to contend with re-entry.

The smaller rocks are composed of those materials in solid state (e.g., ice not water). They are less irradiated as they are further away from the Sun (think the asteroid belt and beyond). Atmospheric entry (if that's what you mean) is irrelevant. What matters here is the transport of materials from a place where they could have formed, to a place where they couldn't.

> Atmospheric entry (if that's what you mean) is irrelevant.

I think the OP meant that Earths magnetic field and atmosphere shields any terrestrial matter far more than than a bare asteroid that has no such protections, so it seems implausible at first glance that these things would develop or survive in open space rather than here.

> it seems implausible at first glance that these things would develop or survive in open space rather than here.

I don't think "organics developed in the vacuum of space" is implied. Survived? Well we have samples now confirming, if I'm understanding the basis for the discussion (the article).

We have some organic ‘building block’ compounds confirmed frozen on some asteroids.

But what we don’t have is any examples of them surviving re-entry.

We also have a massive amount of those same compounds already here on the planet.

Causality is… tenuous. But not impossible.

Causality was not the point. The point was to refute the seeding hypothesis, and because they found those molecules, the effort to falsify the hypothesis failed. Now we can move on to the next attempt to refute, which, as you say, might be to study whether molecules can survive conditions of reentry.

Experiments do not tell us that something IS a certain way; only the ways it is not.

The ideal situation for an expert is to prove causality!

It’s nearly impossible, but it is the holy grail!

This experiment was to try to falsify one theory, yes, but as you note that is a very long way from the actual goal - or the level of certainty that the article is trying to imply.

These articles are written due to funding needs, which is why the articles are the way they are - and why the scientists themselves are likely cringing too when they read these articles. At least until the checks (hopefully) arrive.

I was under the impression that the ejection of these compounds demonstrates that organics (blocks) can escape a gravity well, which implies they can likely re-enter another.

Atmospheric entry is completely relevant because some people have made the illogical claim that meteorites falling on Earth could have contributed with such complex organic substances, like the nucleobases, to the appearance of life on Earth.

The icy bodies from the outer Solar System that contain such organic substances are very easily vaporized during entry in the atmosphere of the Earth, so only a negligible fraction, if any, of the organic substances originally present in such a body would reach the surface of the Earth.

So we get organic vapors in the atmosphere right. Shouldn't that matter?

One theory is that the primitive Earth contained much smaller quantities of the volatile chemical H, C, N, O and S, which are the main constituents of water and of organic substances.

Then Earth collided with a great number of small bodies formed in the outer Solar System, which were rich in water and organic substances. This has modified the composition of the Earth towards the current composition. (Later Earth has lost a part of its hydrogen; because hydrogen is very light, it is lost continuously from the upper atmosphere, after water is dissociated by ultraviolet light; thus now the Earth has less water than around the appearance of life.)

This theory is likely to be true, so meteorites probably have brought a good part of the chemical elements most needed by living beings.

However, most of the pre-existing organic substances from meteorites must have decomposed and whatever has been preserved of them could not have had any significant role in the appearance of life here, because any living being would have needed a continuous supply with any molecules that it needed, otherwise it would have died immediately. Such a continuous supply could have been ensured only for molecules that were synthesized continuously in the local environment here, not for molecules arriving sporadically in meteorites and which would have been diluted afterwards over enormous areas, down to negligible concentrations.

Wouldn't a big enough asteroid have an inner part which survives entry? You seem to be saying that it's impossible for any meteorite that might have these chemicals to not be completely vaporized which seems doubtful. Have you got a source?

So you survived re-entry. Now, you get to survive impact. Seems like the energy released would also be damaging

Most asteroids have slowed to terminal velocity by the time they impact. It’s not nothing, but it’s mostly going to be relevant to physical processes and not chemical ones.

You might consider that scientists advanced enough in their field to be launching missions to retrieve dust from asteroids are actually aware of basic facts relevant to their field of study.

You might consider that even concepts like plate tectonics (which frankly are incredibly obvious if one just looks at a map) were considered ridiculous ideas by the most advanced experts in their field at one point. A point not that long ago.

I’m not saying the person you are responding too is right - but appealing to authority on something like this has a pretty bad track record.

Quality of comments massively dropped on the HN. It feels like Facebook now.

The Redditors have arrived

Generally speaking small molecules aren't damaged by concussive shock.

I was thinking more of heat

The earths poles?

Those smaller rocks are in the outer solar system, where the solar irradiation is lower. But the way they are composed is lots of ices (volatile molecules in solid form) being built on the silicate/graphite refractory core. The ices remain preserved in the environment provided by the outer solar system.

It would’ve been specifically asteroids from beyond the "frost line", where it’s cold enough for volatile substances to coalesce and stay solid.

"volatile substances" is doing a lot of work. This means water and organics. Literal cold-storage seeds of life.

Meteorites are generally cold when they reach the surface of the earth. The heat of reentry is very brief and generally just on the surface. That's my understanding.

The surfaces are typically melted - the ones that don’t just explode anyway.

Icy meteorites never survive re-entry that I’m aware of; and most carbon/chondrite ones don’t either, but they are the most common type that do. They tend to be ‘dry’, however.

Re-entry is a very ‘angry’ process.

Extra terrestrial propagation of life, if real would have evolved to have non-zero survival rates in interstellar radiation regimes and timescales.

The fragility of life-as-we-know-it that has undergone serial passage in an environment largely shielded from radiation, is not necessarily representative of putative life-forms carried by little rocks in space.

I am neither convinced for nor against the idea that life may have been carried over by interstellar rocks: on the one hand, its a major promiscuity between celestial bodies within star systems, galaxies, etc. on the other hand since we haven't discovered other life forms yet we have no idea on the missing probability densities of life in the bulk of the universe, so the Bayesian catapult can swing either way, we just lack the data for now.

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