The Hoba meteorite, estimated at 66 tons, left no crater when it fell to Earth | Hacker News Reader

The Hoba meteorite, estimated at 66 tons, left no crater when it fell to Earth

thevintagenews.com

66 pointsgus_massa34 comments

The explanation for why it didn't leave a crater is pretty unsatisfying.

I was expecting something about the flat shape and how it might have skipped over the atmosphere and/or induced a lot of drag.

I did search a bit but didn't find an article that had both a plausible explanation and some credible source.

There was a crater. Mayne not a giant, but one of some sort. If the soil was soft enough, deep enough, that crater could have eroded away long ago. The rock may also have moved from where it landed to where it is now. So it has, today, not "left" us a crater.

The article also says it was covered... so perhaps the crater filled in by erosion this covering it or it was deliberately filled in by ancient farmers.

Edit: grammar.

I agree. Perhaps shape plus angle of fall and there could have been a thick forest in that place or maybe a lake.

FWIW, humans have survived falls from aircraft without a parachute, due to the last two reasons. Recalling some of the accounts, it helps a lot if you happen to hit on the downslope of a forested hill with just the right slope.

Those things matter at human terminal velocity (not much mind you) but not at asteroid terminal velocity. Asteroids hit with so much speed that the kinetic energy of impact mostly overcomes the binding energy between molecules and even atoms and the impactor largely vaporizes. This is more true for comets which are looser collections of ice and rock, and more true for larger impactors.

Impactors like that have not slowed to their terminal velocity. They either are small enough to be slowed by the atmosphere, bigger and explode in the atmosphere, bigger still and they race all the way the ground.

you're right

Completely off topic, but it really pisses me off that stuff like this gets covered uncritically:

https://blogs.wsj.com/indiarealtime/2016/02/08/meteorite-kil...

> Scientists have suggested that the massive rock apparently slowed down as it penetrated Earth’s atmosphere. It slowed so much that the Hoba reached a point of terminal velocity as it was about to impact the surface

i don't buy it.

why couldnt it be part of a bigger impactor, so if it was just a shard that broke off after impact and flew mostly horizontally before settling?

maybe it struck the top of a thick glacier that has since melted?

maybe there were 200m of water in that location then?

terminal velocity for a meteor is 200-400mph. 66 tons at that speed would at minimum leave it nowhere near the surface.

> why couldnt it be part of a bigger impactor, so if it was just a shard that broke off after impact and flew mostly horizontally before settling?

I agree, there could be any number of explanations. I haven't seen many meteoroids but the rectangular shape appears peculiarly unnatural, more like a fragment of a shell.

No one seems to have proposed that it could have been magnetic and it interacted with Earth's magnetic field.

I don't think the earths magnetic field is anywhere near strong enough to seriously effect a meteorites velocity.

You don't have to guess, you can do the math.

While you're at it, watch this, it's fun (and related): https://www.youtube.com/watch?v=sENgdSF8ppA

Yes, you can do the math. But "practical" intuition gives you a good sense of possible orders of magnitude, though, sometimes fails.

A compass needle is easily moveable by hand. Even Lenz effect forces (when only driven by magnets) are weaker than the attraction forces of the same magnet (depending on the speed, of course) though going east->west the flux doesn't change much.

So my conclusion is that, even though it might have had a small effect on it, absolutely not enough to make it change velocity significantly.

> The Hoba meteorite is an iron meteorite which is the only piece of iron on the Earth not made by men. Author: Digr. CC-BY 3.0

Hmm. The only one? I don't think so.

Yeah, that verbiage also caught my eye. I think they might have been trying to say something like

   iron meteorites are the only pieces
   of iron on the Earth not made by men

Which, depending on the definition of the words "on the Earth", isn't much better. After all, iron is an element and, according to Wikipedia: is by mass the most common element on Earth, forming much of Earth's outer and inner core.

The USA has a very large iron meteorite on display. It was "stolen" from native peoples in Oregon and eventually "stolen" again by New Yorkers and put on display.

https://en.wikipedia.org/wiki/Willamette_Meteorite

Despite my use of "stolen", I think NYC is a great place for something like that. As a child I saw this meteorite in the American Museum of Natural History.

Museums are great places. At least 1000x as many people have seen the Willamette Meteorite than have seen the Hoba meteorite.

Yes, I actually live in West Linn, OR, and that's what caught my attention since it's kind of famous around here. I had also recently been reading about the dagger found buried with King Tut, which seems to have likely come from a meteor. https://en.wikipedia.org/wiki/Tutankhamun%27s_meteoric_iron_...

That's ... PR.

The Hoba is ~ 84% iron. The Meteoritical Society records over 1200 'Iron meteorites' (FeNi-alloys) https://www.lpi.usra.edu/meteor/metbull.php?sea=&sfor=names&...

Hoba's type is Iron, IVB. It's by far the largest -of that type-.

The Cape York (from Greenland, Melville Bay) is type IIIb. (Both octahedrites.) https://en.wikipedia.org/wiki/Cape_York_meteorite It's total weight (at least 8 large pieces) is comparable, and its story is much more interesting ... the Inuits used it to make iron-tipped weapons, which caught the explorers' eyes. http://evols.library.manoa.hawaii.edu/bitstream/handle/10524...

A 66 ton chunk of iron falling on earth probably before any iron had been smelted by humans.

Now think about the equivalent meteorite falling today: what substance could it be comprised of that we haven't synthesized or seen yet? Maybe an exotic isotope of an otherwise common element which demonstrates some exotic properties. Superconducting at room temperature maybe.

Amazing to think about what asteroids could be out there headed our way (and not big enough to destroy everything).

There's a Stephen Baxter novel from a quarter of a century ago [1] in which an antimatter meteorite falls to earth, and via undisclosed handwaving, ends up as a deposit in the Antarctic, which is subsequently mined to provide a source of power for various steampunk shenanigans:

https://www.thebooksmugglers.com/2010/04/steampunk-week-book...

[1] yikes

Vibranium would be pretty cool.

With just the right spin, you might get a skipping-stone effect (given the shape shown) on the atmosphere or ground or both.

for scale:

http://triplicit.com/wp-content/uploads/2016/09/DSC_7846-2.j...

thank you google

I have a serious question about the meteorite extinction case...

People talk about populating mars as insurance against a devastating meteor attack wiping out the population.

Wouldn’t it also work to create a large shock-absorbing facility on earth? If a meteorite is headed toward earth, you could simply enter the shelter, wait for it to hit, and then come back out.

Of course then you’re dealing with interrupted ecosystems, but it’s hard for me to believe that they would be worse than Mars.

P.s. I know populating Mars is considered diversification for other reasons, but a mass extinction is certainly a reason given.

"Wouldn’t it also work to create a large shock-absorbing facility on earth?"

Yeah, sure. would be possible. Simple physics.

The crater Chicxulub absorbed more Energy than a billion times the energy of the atomic bombings of Hiroshima and Nagasaki.[1] So you basically would just need a hell of an airbag. Hey, if you do it right and you can harvest the energy then you can run the world electricity supply on it for a few years.

[1] http://doc.rero.ch/record/210367/files/PAL_E4389.pdf

Not to mention we would need to survive the aftermath - possibility of debris kicked up into the atmosphere blocking the sun for months or years, chain reaction of volcanic eruptions with the same side effect plus lava, mass plant and wildlife die-off leading to possible global ecosystem collapse, raised global temperatures and water levels, and shifting tectonic that could possibly shift elevations and flood wherever this 'facility' is located. I'm sure there's many other issues I haven't thought of off the top of my head.

well there is the glow from the returning ejecta turning the entire sky into a broiler oven for a few days ... hate it when that happens, control of the planet goes back to to the meek who were hiding deep underground at the time.

It wasn't the pressure wave from the impact that caused the extinction. It was the sun-blocking cloud of dust and debris that got thrown into the atmosphere for years afterwards, dramatically cooling the climate and killing the vegetation that forms foundation of the food chain.

You may be underestimating the damage to ecosystems. The Yucatan Peninsula asteroid strike threw a massive amount of small particles of rock and other junk high into the atmosphere, which burned up due to atmospheric friction falling back. It would have appeared on the ground as an amazing meteor shower, so intense the the sky would be glowing from the light of the burning particles. This was widespread enough to surround the planet.

That lasted for hours, bathing the surface in intense infrared radiation. It was on the surface like being in an oven with the broiler on. Animals and plants not underground, underwater, or well sheltered such as in caves were killed either by heating from the infrared radiation, or by not being able to cope with breathing an atmosphere that was now something like 200 C.

If we arranged for all humans to be sheltered during such an event so we don't get wiped out during the worldwide broiling, we'd have lost pretty much all of our food chain except maybe seafood.

So lets assume we also make sure to shelter plants and animals, so that when we can come out of the shelter we can start replanting and start breeding food animals.

The climate would be wonky for a long time. That's one of the things that doomed many species that were not killed during the broiling phase after the Yucatan Peninsula strike. The climate where they live changed to something they could not cope with.

Humans could deal with that better. After we get out of the shelters and want to replant food crops, we would not be constrained to just planting them where they had been before the impact. We can examine the whole world and plant our recovery crops where they have the best chance of surviving. Same with breeding recovery animals.

This would require a level of cooperation that I doubt current governments can achieve peacefully. I'd expect several wars would be involved in settling the resource allocation issues.

My guess is that far future galactic anthropologists will discover that when civilizations that have reached a technology level that allows them to see a big strike coming far enough ahead to prepare for it, but have not reached a level where they can stop it get hit, their survival chances go way up if either

(1) they have a strong planet-wide government, or

(2) they have a strong sense of being one people, without dividing themselves by race, religion, politics, or region (they may have different races, religions, and so on but treat differences in them the way we treat differences in, say, what kinds of food you like or what genres of movies you like).

Both of those help enable the kind of cooperation needed to recover.

It always seemed to me that if we could populate Mars, we should be able to populate a self-sustained under-water or subterranean colony.

Such a colony would provide practice at designing biospheres, and could be pretty robust against space hazards, with much shorter round trip times while testing it, if we're really convinced we need a lifeboat for Earth using existing tech.

(Though I suspect we partly want to colonize Mars because space is cool, which is fine too.)

An interesting story about a meteorite, but what struck me was a sign of the deification of Google ... a reader comment after the article reads: "Wonderful description and High Quality Pictures. >>> Thanks Google<<< " -- emphasis is mine.

The source material, writing, comments system tied to the article all have nothing to do with Google, yet the reader is attributing their joy in the article to Google. I've seen Google deified in jest, but I don't think the reader here is anything but serious.

Praise Google, Glory Be to Google, Google is Good, Google is Author of All That Brings Us Joy. Google's Yoke is Easy and Their Burden is Light ... Google only asks for your email and search/location/browsing history. We Are Google's Image. Come to Google Just As You Are.

(Full Disclosure: I am happy to make the trade with Google ... for some reason I trust Google and Amazon, don't think Apple has a clue outside their hardware & associated software, and hate Facebook / Twitter.)

Among its many other offerings, Google does still sport a quite serviceable search engine. Perhaps the commenter simply meant to convey that that was how they found the article?

It struck me too.

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