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Comment by lucb1e | Hacker News Reader

Pardon my ignorance, but as I was typing a message in a chat group linking to this page and briefly mentioning why these rocks are special, I realized that we already have a ton of asteroid material on earth. I get that the outer layers will have burned in the atmosphere, but inside is still intact. Is this useful because we suspect the surface contains different materials? Or the crushing of it on impact? Or is there something else that makes this different from digging up one that came to us rather than us going to them?

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Meteorite samples are far from perfect surrogates for asteroids, though. They experience extreme pressures and lose a great deal of their bulk when falling through Earth’s atmosphere. Once they land, they pick up contaminants from the terrestrial environment that are hard to distinguish from native substances. Pristine samples from an asteroid might not only answer questions about the origins of life’s chirality but also offer clues about how water ended up on Earth. One hypothesis suggests that asteroids, which contain some water, may have also seeded it onto our home planet during collisions (Science 2014, DOI: 10.1126/science.1261952). [0]

[0] https://cen.acs.org/physical-chemistry/astrochemistry/tale-2...

They shot a probe out into space, had it land on an asteroid, slam a slug into it to get below the surface, land on it again, and pick up rocks. In an era where the headliners are delivery and ride sharing apps, it's worth stepping back and considering this achievement for what it is.

Maybe the rocks themselves aren't special, but where they came from and how we got them is a massive achievement.

Most of the advantage is in tech demonstration [1].

Scientifically, retrieved samples are pristine and more massive, for a single body, than terrestrial samples. Retrieval also enables sampling non-NEOs.

That said, I think your intuition is correct. The scientific value of these missions pales next to their technological value.

[1] https://spacenews.com/op-ed-10-reasons-why-an-asteroid-redir...

> Scientifically, retrieved samples are pristine and more massive, for a single body, than terrestrial samples.

They also provide ground truth data. We know that the imaged samples 100% came from an asteroid, and a particular asteroid, whose characteristics we know from observation and other measurements. That's in contrast to terrestrial samples, for which we have to make educated guesses as to the properties of the bodies they came from. The former will be useful to cross-check and callibrate the latter.

I would prefer the description "tech development" to "tech demonstration". I never do any non-trivial tech project without learning some lessons about how I would do it differently next time. So we go out and see what's on a particular asteroid, but we also see things about the task. The next time, we try a modified approach and go see what's on a different asteroid. We build out our knowledge of what resources are already out there, and where, while building out our knowledge of how to get out there, do things, and get back.

And when you get both A and B, the relative value of A vs B may be as claimed, but what really matters in the cost/benefit analysis is the value of A+B.

And even the value of the science is an interesting question, because science that finds what we "already know" has some value, but not much, but science that finds what we never expected changes history. And in our estimates of scientific value, we never expect to find what we never expected.

I believe there is also a good way to prove that some models work as we expect.

I mean, we have now hard evidence that an given asteroid has properties X, Y, Z - and we have mathematical (or ML) models that infer such properties from indirect measures.

At least, we have evidence to validate that models or spot errors on them with ground truth.

To quote the Hayabusa2 team directly (http://www.hayabusa2.jaxa.jp/en/topics/20201204_ts3/) :

> You might therefore wonder if we should instead analyse meteorites. However, meteorites consist of the material that is left over after re-entry through the atmosphere and their structure, along with easily volatile substances, have been lost. They will also be contaminated with substances from the Earth. On the other hand, samples from the asteroids are brought back to Earth in the same condition as they were in space, with the “re-entry capsule” protecting the sample through the atmosphere and landing.

Asteroids on earth have been changed by the environment on earth. Part of it during entry, part of it during impact, part just lying there for long times.

The Ryugu sample provides an opportunity to check our understanding of the changes that happened to asteroids on earth.

Contrary to random pieces falling onto earth they are from a specific astroid and not impacted by earth atmosphere (which burns those stones quite a bit)

Thus they potentially reveal more details and allow comparison with planets and other objects, which might help to identify the origin of the astroid and in turn be a piece in the big story how our solar system came together.

Don't organic molecules break down when getting cooked in the atmosphere? Perhaps they'll find some chemistry that doesn't normally survive the fall to Earth.

IIRC a key thing that makes it special is that it's the first time an asteroid has ever been mined

Hayabusa 1 overcame massive hurdles and then sacrificed itself to deliver it's sample 10 years ago. It was very small - less than one gram - but first.

Still nice to see such a big sample mass increase as well as managing to get it without harming the main probe, which can continue to do more science. :)

I'm sure the poster appreciates the achievement but the question remains whether these samples tell us something more than samples collected on earth.

> I realized that we already have a ton of asteroid material on earth.

The quantity isn't as high as you might expect.

Most meteor flux is from cometary dust, not asteroids. The Geminids and Taurids are asteroid in origin but no meteorites have been traced to those showers.

Once the atmosphere and oceans take care of the majority, only about 10 meteorites of asteroid origin are recoverable each year.

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