Better for an asteroid to hit water or land?

[Altair33]

Assume that a 1 mile diameter asteroid is heading to earth and nothing can be done to stop it. Would it be better for the earth for it to land in the ocean or on land? Which location on earth would cause the most damage and which would cause the least?

[Paul_in_Qatar]

Central Australia would probably be as good as it could get. Antarctica might be good to. Someplace on Japan so as to smoosh the big cities and cause a huge wave for bonus points might well be the worst-case.

[msmith537]

Land

The asteroid would create a 20 mile wide crater, a several GIGAton explosion, global firestorms and billions of tons of white hot flaming ejecta (crap that gets shot into space that soon brings bad news someqhere else) no matter where it hits. The only difference is that a water (the statistically more likely location) you experience the joy of tsunami.

[Altair33]

@msmith537

Land

The asteroid would create a 20 mile wide crater, a several GIGAton explosion, global firestorms and billions of tons of white hot flaming ejecta (crap that gets shot into space that soon brings bad news someqhere else) no matter where it hits. The only difference is that a water (the statistically more likely location) you experience the joy of tsunami.

I read somewhere that all the vaporized water would also cause unimaginable global rains and resulting flooding. So my impression is also that land would be better for the earth as a whole.

[Bill_Door]

I agree with those who say land is best. The white hot crater will radiate heat to space, while an ocean landing will turn that heat into steam and keep it in the atmosphere.

[bouv]

But in the long term wouldn’t water be best? All that particulate matter getting into the atmosphere from hitting land has to be worse than just a lot of water vapor.

[Chronos]

Antarctica would probably be best, for three reasons: First,the ejecta will be largely water, which would precipitate out (relatively) easily. Second, if you hit the continent, you won’t get a tsunami. Third, most of the atmospheric effects won’t cross the equator, and some won’t even cross the antarctic convection cell boundary, and the southern hemisphere is less populated than the northern.

[constanze]

The worst place is one of the hot spots or hot belts: where some plates are under so much pressure, that lots of volcanoes and earthquakes happen all the time. If the asteroid hits there, then on top of the effects listed above, you’d get huge eruptions from the volcanoes there (which means additional sulfur in the atmosphere, to the stuff that the asteroid itself throws up), and lots of magma from the inside of the Earth, too.

[BMax]

@constanze

The worst place is one of the hot spots or hot belts: where some plates are under so much pressure, that lots of volcanoes and earthquakes happen all the time. If the asteroid hits there, then on top of the effects listed above, you’d get huge eruptions from the volcanoes there (which means additional sulfur in the atmosphere, to the stuff that the asteroid itself throws up), and lots of magma from the inside of the Earth, too.

If it strikes Indonesia or Hawaii, say half on an island and half in the ocean, we could have all those effects and a tsunami.

[Shot_From_Guns]

@BMax

If it strikes Indonesia or Hawaii, say half on an island and half in the ocean, we could have all those effects and a tsunami.

Ooh, ooh, Mommy, I want **that **one!

[Polycarp]

Out of curiosity, how large were the Chicxulub “dinosaur killer” and other similar geological-history impacts, compared to this hypothetical imact?

[Quartz]

Wiki says that the Chicxulub bolide was at least 6 miles in diameter. So a bolide 1 mile in diameter is going to be at most 1/216th as massive.

[The_Great_Philosopher]

A mile-wide asteroid impacting with land would be disastrous - it would probably throw enough particulate into the air to block out the sun to some extent for years afterwards, all over the Earth. That would significantly lower temperatures and it’d inhibit plants from photosynthesizing, potentially wrecking entire food chains. Depending on the type of rock it landed on it could also create global - severely poisonous - acid rain, and there’s theories that it would cause global forest fires as well as the flaming debris was pulled back to earth after being ejected beyond the atmosphere. If the asteroid landed in relatively shallow water all of those things could probably happen anyway, plus megatsunamis to boot.

Based on that maybe the best place it could land would be in very deep water, like over the deepest parts of the Pacific, where it would get slowed down by 6 miles of water before impacting. On the other hand, maybe that would create tsunamis so big they’d wipe out anything vaguely near the Pacific, or maybe something terrible would happen to do with the amount of water vaporised…

To be honest, I think anywhere it landed would be fairly catastrophic…

[Der_Trihs]

@Bill_Door

I agree with those who say land is best. The white hot crater will radiate heat to space, while an ocean landing will turn that heat into steam and keep it in the atmosphere.

This. A water landing means more energy stays here on Earth, instead of getting blasted/radiated into space. And as I understand it, that hot spot in theory could generate super-hurricanes, more powerful than anything normal climate can produce.

[Satellite_Guy]

Would an impact caused by this asteroid on land be felt on the opposite side of Earth?
If not, how big would it need to be before it could be felt?

S^G

[FoieGrasIsEvil]

@The_Great_Philosopher

A mile-wide asteroid impacting with land would be disastrous - it would probably throw enough particulate into the air to block out the sun to some extent for years afterwards, all over the Earth. That would significantly lower temperatures and it’d inhibit plants from photosynthesizing, potentially wrecking entire food chains. Depending on the type of rock it landed on it could also create global - severely poisonous - acid rain, and there’s theories that it would cause global forest fires as well as the flaming debris was pulled back to earth after being ejected beyond the atmosphere. If the asteroid landed in relatively shallow water all of those things could probably happen anyway, plus megatsunamis to boot.

Based on that maybe the best place it could land would be in very deep water, like over the deepest parts of the Pacific, where it would get slowed down by 6 miles of water before impacting. On the other hand, maybe that would create tsunamis so big they’d wipe out anything vaguely near the Pacific, or maybe something terrible would happen to do with the amount of water vaporised…

To be honest, I think anywhere it landed would be fairly catastrophic…

I agree with a remote ocean location. There may very well be tsunamis, but they would only wipe out coastal areas and there would be significant warning time to evacuate. And most coastal areas don’t produce a lot of essential foods, especially grains. We may suffer from a loss of fruits from California and Florida depending on where it hit, but that is a better alternative than…

On land, the resultant dust cloud over our atmosphere would affect everybody in severely negative ways. Crops would not grow. Rain would be acid. The Sun would not shine. Air would be full of particulate matter.

I vote remote ocean location.

[Der_Trihs]

@FoieGrasIsEvil

On land, the resultant dust cloud over our atmosphere would affect everybody in severely negative ways. Crops would not grow. Rain would be acid. The Sun would not shine. Air would be full of particulate matter.

You’d get much the same thing from an ocean strike; massive amounts of vaporized water punched high into the atmosphere instead of ( or alongside ) dust.

[billfish678]

@Der_Trihs

You’d get much the same thing from an ocean strike; massive amounts of vaporized water punched high into the atmosphere instead of ( or alongside ) dust.

The big difference IMO would be that all that water vapor would lead to short term global warming, while mostly dust from a land impact would lead to short term global cooling, which would be much more catastrophic IMO.

I also suspect that the water vapor would work out of the atmosphere faster than the dust.

[Der_Trihs]

@billfish678

The big difference IMO would be that all that water vapor would lead to short term global warming, while mostly dust from a land impact would lead to short term global cooling, which would be much more catastrophic IMO.

Actually, it would probably produce global cooling, since it would condense as clouds. Then when it became transparent, it would produce global warming.

@billfish678

I also suspect that the water vapor would work out of the atmosphere faster than the dust.

I doubt it; water vapor is lighter.

[chorpler]

Well, if you trust the guys that Larry Niven and Jerry Pournelle talked to during their research for Lucifer’s Hammer, the water vapor would lead to cooling as well, because the earth would be shrouded in clouds and would reflect a lot more light. The very informative “cubic mile of hot-fudge sundae” scene, where a bunch of people at JPL are discussing what a cometary impact would do to Earth for a Cosmos-style TV special, and they decide to do the calculations using a cubic mile of hot fundge sundae as an example, goes into detail about this:

… “It probably hits water. If it hits land, it’s tough for anyone under it, but most of the energy radiates back out to space fairly quickly. But if it hits water, it vaporizes it. Let’s see, ergs to calories . . . damn. I don’t have that on my gadget.”

 "I do," Forrester said. "The strike would vaporize about sixty million cubic kilometers of water. Or fifty billion acre-feet, if you like that. Enough to cover the entire U.S.A. with two hundred and twelve feet of water."

 "All right," Sharps said. "So sixty million cubic kilometers of water go into the atmosphere. Harvey, it's going to rain. A lot of that water is moving across polar areas. It freezes, falls as snow. Glaciers form fast . . . slide south . . . yeah. Harvey, the historians believe the Thera explosion changed the world's climate. We know that Tamboura, about as powerful as Krakatoa, caused what historians of the last century called 'the year without a summer. Famine. Crop failure. Our hot fudge sundae will probably trigger an ice age. All those clouds. Clouds reflect heat. Less sunlight gets to Earth. Snow reflects heat too. Still less sunlight. It gets colder. More snow falls. Glaciers move south because they don't melt as fast. Positive feedback."

 It had all turned dead serious. Harvey asked, "But what stops ice ages?"

 Forrester and Sharps shrugged in unison.

 "So," Hamner said, "my comet's going to bring about an ice age?" Now you could see the long lugubrious face of his grandfather, who could look bereaved at a $60,000 funeral.

 Forrester said, "No, that was hot fudge sundae we were talking about. Um—the Hammer is bigger."

 "Hamner‑Brown. How much bigger?"

 Forrester made an uncertain gesture. "Ten times?"

 "Yes," said Harvey. There were pictures in his mind. Glaciers marched south across fields and forests, across vegetation already killed by snow. Down across North America into California, across Europe to the Alps and Pyrenees. Winter after winter, each colder, each colder than the Great Freeze of '76‑'77. And hell, they hadn't even mentioned the tidal waves. "But a comet won't be as dense as a cubic mile of h‑h‑h—"

 It was just one of those things. Harvey leaned back in his chair and belly‑laughed, because there was just no way he could say it.

So unless models of impacts have changed significantly in the last 30 years, a land strike would apparently be better than an ocean strike.

ETA: On preview, I see Der Trihs has made this point too.