Is this sudden global cooling scenario plausible?

Question

In the year 2071 the Dysnomia incident happened. The Dysnomia (a mining ship) suffered a catastrophic failure and violently exploded sending its payload, an aged comet, hurtling towards earth. The comet proceeded to rip apart in the atmosphere distributing a massive amount of dust in the stratosphere leading too catastrophic global cooling. This global cooling forces a large portion of the human race to move into arcologies and urban areas, mostly abandoning the country side.

But is this series of events even plausible? That's what I'm stuck on is how to physically have these series of events unfold without:

• a massive impact (smaller ones are acceptable)
• blocking out the visibility of the sun (dimming is fine)
• Not too severe cooling that GMOs couldn't be bred within a few years to adapt to the new climate (most agriculture would move to vertical greenhouses however)

Answer 1

At the right angle of impact a comet could get reasonably deep into the atmosphere before skimming off back into space. Usually that wouldn't leave behind a lot of material but a comet that had lost most of it's surface volatiles may be coated in a thick, but loose, crust of materials with a higher boiling point. Some of that crust would slog off into the atmosphere due to mechanical friction and heating during the comet's dip into the air. This crust forms naturally on comets as they get exposed to repeated doses of solar radiation and has been observed on an number of objects by comet survey probes.

To cause long term (more than a year or two) cooling the compounds you want to dump into the atmosphere are Sulfur Aerosols. Comets usually do have some sulfur but it's not usually a major component of their chemistry so the ship would have gotten lucky, or unlucky, to find one with that much sulfur in it. The degree of cooling is directly proportional to the concentration of sulfur that eventuates from the atmospheric impact event.

If the angle and momentum of the object is just right, or wrong depending where you're standing, when it first skims the atmosphere it will enter into an unstable orbit with deeper and deeper brushes into the atmosphere until it burns up completely or what's left of it lands, but usually it will hit once and then carry on.

Answer 2

Been there, done that!

This apparently happened already 1,500 years ago. Scientists at Cardiff University, UK, believe they have discovered the cause of crop failures and summer frosts some 1,500 years ago – a comet colliding with Earth.

So the only part that is tricky, other than fine-tuning the size of the comet to come up with just the right amount of sun-dimming dust, is to figure out how a ship would capture a comet. Based on other things I've read, I think capturing an asteroid or two would be a lot easier than a comet. Comets have very large orbits, so they are moving pretty quickly when they get near Earth. Asteroids have more "typical" orbits. There have even been serious real-world proposals to capture & mine small asteroids using near-future technology, though to capture one that would be large enough to cause a nuclear winter would require some significant engineering advances.

Answer 3

First, start with massenkatz' answer above. Then let us change 'comet" to "icy Kuiper Belt Object". Now if we accept what is valuable about this comet is the water, I think we have a possible scenario we can imagine that makes some economic sense.

We are no longer dealing with objects with highly eccentric initial orbits, but we do have the new problem of getting an Icy rock from Pluto's orbit back into the "industrialized space zone" closer to earths orbit. But the water resource is valuable and expected to remain so for generations as water itself is needed by the vast human population for life and the heavy hydrogen isotopes present in the ice are needed for energy production, so governments and companies can take a long view when designing their water supply chain. At any time there will be tens of thousands of icy bodies at various stages of de-orbiting towards earth in a process that takes generations to complete.

They arrive at this: manned or robotic survey ships travel to the belt. They locate good prospects by water/mass ratio, industrial value of non-water content, and viability of revisable orbital dynamics.

They have brought a host of small tugs. These are simple ion drive engines capable of delivering small but constant thrust continuously. They are attached to the target object along with a control module and this package begins the job of returning the object to orbit between mars and earth. Meanwhile, the survey ship moves to find its next target. It has supplies to recover 1000 such objects.

The return orbit of any body is very slow and complex. The ion thrust is very small, so even with an initial boost from another more energetic engine, changing the bodies orbit will take a long time. So, objects use gravity assist whenever possible. First with other Kuiper belt objects, then with planets and asteroids, the planned deorbit involves a series of encounters to first boost velocity and adjust trajectory, then degrade velocity and park the object in an orbit where it can effectively be harvested.

No two deorbits are the same. Companies deploy surveys to take advantage of possible gravity boosts from known high mass Kuiper Belt Objects and outer planets and their moons to return payloads as rapidly as possible using the fewest tugs but only the rarest and most favorable orbital dynamics result in return journeys of less than 250 years.

The incident that eventually sends one of these bodies to earth could happen anywhere along the supply chain, leaving earth with a lot, or almost no warning of the coming catastrophe.

Answer 4

It sounds good but the population would have to move to the countryside rather that urban areas to be closer to food and water and it would be pretty massive.

The dust would likely cause respiratory issues. It would be possible for the dust to be thin enough that the sun shines through but then the dust would settle quickly.

Answer 5

If you want realism, I'd be a bit concerned about the comet's contents. We have visited a comet now, so we have good information to go on.

If your comet was worth bringing back to earth, then whatever it is made of, must be valuable enough to justify the effort, and also capable of creating a persistent aerosol of dust or other material on atmospheric breakup, that is capable of triggering a cooling episode. Combined with current knowledge of comet contents, that might be quite a limiting problem.

If a warming effect was needed, then methane might be a valid answer. But for cooling - that amount of dust suggests a solid rocky comet, not a frozen one, and I'm not sure how well that fits current scientific knowledge.

Answer 6

Later: I was just passing by, and noticed that I got carried away and forgot perhaps the main point — “without… massive impact…”. Sorry about that.

New thought. I know you can “drill” through rock using sound vibrations — or at least there are YouTube videos on this that look very convincing (they run the sound vibrations through a piece of metal that is pressed against the rock). (I just searched “youtube sound rock drill Egypt”; perhaps use “melt”.) Perhaps you could have some industrial-level system for vibrating a rock into dust. In the outlier case, the rock would be completely powdered before the mining ship ever arrived in orbit. (They could even have it already neatly sorted into bins by material type!)

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From the other answers… it looks to me as though it would be handy for the accident in question to disintegrate the comet. Offhand, you could have

• an object of sufficient mass, travelling at sufficient speed, collide with the ship/payload,
• the ship/payload crash into a sufficiently massive “stationary” object (at a sufficiently high speed), or
• an erroneous or accidental military attack (perhaps with an energy weapon?).

Alternatively, you could have the comet on a collision course with Earth, because of an engine/steering malfunction or failure on the Dysnomia — the comet thus does not have to be moving especially fast — and have someone deploy a nuke/laser/whatever to blow it up, as an act of self-defence — rightly or wrongly. This might give you the option of having nuclear fallout play a part in the disaster — perhaps from the ship rather than from the weapon. (Or maybe the Dysnomia was also carrying some other cargo that is dangerous to human beings (or bees…), or simply might be dangerous.) (This frees you from having to have the comet be both valuable and dangerous (citing “Stilez”).)

[ Edit — response to “L.Dutch - reinstate Monica” comment.
Hmmm. I guess I was thinking of an arrival decelerating to an orbit height… but, as you have pointed out, that is not orbit [blush]; it would involve accelerating laterally, and coming in at a tangent would be better. …And everything (else) is moving fast.
Two objects in the same orbit but in opposite directions would do as I described; this would require either multiple orbital directions or catastrophically bad navigation (or perhaps mostly just being “upside down“ (and blind) ). Another thought: maybe it is the other object that has the dangerous cargo.
Another possibility: a third party comet coming in obliquely through the orbital traffic — perhaps another Oumuamua, for the unexpectedness. (In this case, the Dysnomia would not have to be carrying a comet (and could be the one carrying the dangerous cargo).) ]