Model suggests asteroids that come close to Earth are torn apart by its gravity | Hacker News Reader

Model suggests asteroids that come close to Earth are torn apart by its gravity

phys.org

41 pointswglb21 comments

Ummm... do you really need a model for this? It has been long known as a fact.

It is called Roche limit (https://en.wikipedia.org/wiki/Roche_limit).

A lot of asteroids are so loosely bound together that you could disperse them by blowing on it. Gently. Honestly, just staring angrily could probably do the job.

They have barely enough gravity to keep themselves together (to counteract their rotation) and getting close to any heavier bodies can exceed that limit and they can spin themselves apart before they even get into Roche limit.

The beginning of the abstract: "Numerical modeling has long suggested that gravitationally-bound (or so-called rubble-pile) near-Earth asteroids (NEAs) can be destroyed by tidal forces during close and slow encounters with terrestrial planets. However, tidal disruptions of NEAs have never been directly observed nor have they been directly attributed to any families of NEAs. Here we show population-level evidence for the tidal disruption of NEAs during close encounters with the Earth and Venus."

Sure, that's fine, but that's not something that really needs evidence.

General relativity is something that needs evidence. It EXTRAPOLATES new knowledge from our existing knowledge.

Loosely bound asteroids, on the other hand, are things that are well within our knowledge.

I don't need an evidence that throwing an astronaut off an airlock is going to kill them. We've never tried doing this but that doesn't stop us from being able to pretty firmly say that they are going to be dead pretty quickly.

For asteroids, we know that lots of them are just piles of rock unbound in any other way than gravitationally. We have actually shot them with things to verify it. We have well tested formulas that are not extrapolations that tell us exactly what is going to happen when we bring together a loose pile of rock and start spinning it. We also have formulas that can tell us exactly what kind of forces are going to be acting on a loose pile of rock of certain mass and diameter when it is shot through a gravitational field.

There is very little uncertainty about what is going to happen. Just because we have never saw it happen does not mean we need any further evidence for this. Doesn't mean there is anything wrong about preparing evidence. It just means it is not very interesting.

How is this different than the Roche limit? If a big thing gets too close, as it whips through a gravity well tidal forces will pull it appart. I thought this was a rather settled field. It happened to the shoemaker comet in 94. That was jupiter but the same thing should happen near to earth, just much nearer.

This was my first thought as well. I haven't read the article yet, maybe I'll learn...

Edit to add: read the article, it sounds exactly like it's the Roche limit, applied to passing objects instead of orbiting objects.

It does. A fast pass through a gravitational gradient by a pile of rubble is going to rearrange the rubble a bit. What happens can be simulated, and someone did that back in 1998.[1] There are pictures of the simulation result. Objects moving fast enough don't get disrupted. "Our results indicate that this limit is well below the mean encounter speeds of long-period comets with Earth. Thus, we predict that few comets ever undergo strong tidal disruption in the terrestrial planet region."

Since 1998 many more near-earth objects have been found, because more automated equipment is looking for incoming threats. Don't know about speeds. Looking back at the 1998 simulations using new data might be useful.

[1] https://www.sciencedirect.com/science/article/pii/S001910359...

The paper has to do with Roche limits, but is not claiming to have discovered the phenomenon.

The novelty is that it provides the first evidence of what earth's Roche limit might be, and a model of how earth interacts with nearby asteroids.

If you

If you what?

It's clear from context, there's obviously a

gesundheit

He probably got shut down by some mice. Hopefully he isn't not the late slartibartfast.

We don't question Big Comet here; those who do are taken care of.

Yes, this is the Roche limit tidal effect pulling apart loose rubble-pile asteroids and comet remnants, as opposed to intact 'solid rock' asteroids.

Things breaking apart in orbit is the premise of Seveneves by Neal Stephenson:

> Seveneves is a hard science fiction novel by Neal Stephenson published in 2015. The story tells of the desperate efforts to preserve Homo sapiens in the wake of apocalyptic events on Earth after the unexplained disintegration of the Moon and the remaking of human society as a space-based civilization after a severe genetic bottleneck.

* https://en.wikipedia.org/wiki/Seveneves

Well yes, but in seven eves, the moon fragments collided, creating more and more fragments exponentially.

Aren't asteroids very varied in terms of compactness? Aren't some asteroids piles of rubble and some others really hard rocks? Maybe I am confused but I'd guess this would also play a role?

The Roche Limit specifically applies to loose, gravitationally-bound bodies.

Chemically bonded objects e.g. solid rock or a huge diamond could approach closer to the planet without breaking up due to tidal forces, depending on the bulk material strength and melting point.

That's what the dinosaurs said.

very cool that earth has it's own defence mechanism

Didn't work very well for dinosaurs.

Maybe the model shall be adapted to reality. /s

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