The Time Machine thread got me to thinking about the extinction event 65M years ago. Say you were somehow (time machine) able to observe the day that rock hit the earth. What events happen?
Would the approaching rock be visible on the ground? For how long?
When it hits the planet, is there enough force to feel it on the other side of the planet? Do seismic waves only travel so far?
After impact, what are the mechanisms? I assume there was a big tidal wave. How tall and how far did it travel?
I’ve also heard worldwide firestorms described. How fast do they travel? Why do they become global?
I sure hope my Time Machine has a protective shield and is able to return to the future on a dime.
Not a physics major, but I can tell you that there have been lots of publications that answered these questions. Plenty of imagined variations on how things might have appeared to those on the ground.
Basics:
how soon the asteroid was visible, would depend on how big it was. Once it began to enter the outer atmosphere, it would begin to heat up and glow, and be visible then. It is also not known how fast the asteroid was moving relative to the Earth, so how long it took to reach the ground is unknown.
Yes, there is a limit to how far seismic waves travel, which varies according to the density and elasticity of the particular materials where they begin.
Here ya go. (Discovery channel’s simulation of a 500-km asteroid impact in the Pacific.) Executive summary: Everything dies.
And here is an hour long program (with lots of commercials) on the last day of the dinosaurs. That one was smaller, 10-km, so only 75% of animal species went extinct.
It is not even known for certain a single asteroid caused this, although it is a likely candidate. Estimates of the asteroid size vary from 10 km to 180 km in diameter, and they have little idea of the approach trajectory or time of year (ie earth’s position around the sun).
All of those would affect whether it was observable and for how long. In some cases like the Russian Chelyabinsk meteor, it appraoched from a direction difficult to see so there was essentially no warning. Chelyabinsk meteor - Wikipedia
In other cases there could be significant warning – weeks, months or even years.
Re the impact effects, this varies widely based on diameter, mass and velocity.
There are various impact effects calculators on the web. You can enter various parameters and see the results:
There have been various visual simulations of large impacts:
Not the same thing, but here is a good CG simulation of what the moon would look like if orbiting at the altitude of the International Space Station: https://www.youtube.com/watch?v=oBDZtt0vWD8
There is some recent doubt about whether there were really global firestorms. However note that the theory is NOT that fires ignited at the impact site and then spread around the world. The theory is that the impact ejected large amounts of material high enough that it rained down all over the planet. As it descended, it would be heated to incandescence by its (second) passage through the atmosphere, igniting planet-wide fires wherever it landed.
Any 180 km diameter estimates were made by people who didn’t understand that craters made by impactors are always much much larger than the impactor itself. The inner crater, which was first discovered, is about 180 km in diameter; the full crater is about 300 km. Most estimates I’ve seen are not much different than 10 km.
You can google videos of meteors like the one that struck Russia a while back. A dinosaur-killing type of asteroid will look similar, just bigger.
The impact from the Chicxulub meteor was freaking huge. The thing hit down by the Yucatan peninsula in Mexico and debris from the impact has been found as far away as Texas and Tennessee. A huge amount of hot stuff was kicked up into the atmosphere, and rained down all over the world, causing the entire world to burn.
The shock wave from a large impact like that does travel all the way around the world, and all of the shock waves come together at what is called the antipodal point, or the point exactly opposite on the globe from the impact. Debris from the impact alone kicked up a dust clout that blocked out sunlight and was enough to cause global winter-like conditions. There’s some debate about exactly how much the shock wave from the Chicxulub affected volcanic activity on the other side of the world, specifically in the Deccan Traps in India, but that increased volcanic activity would have kicked even more stuff into the atmosphere, making the artificial winter even worse.
Needless to say, it was not a happy time to be living on Earth.
A 10km asteroid should be visible as a faint star about a million kilometres away. At that point you have about 13 hours to impact. It would slowly get brighter and brighter, but it would not really be spectacular until it reached the top of the atmosphere a few seconds before impact, at which time it would compress the atmosphere to a brilliant glow in front of it.
The actual impact with the Earth’s surface would be brighter still. At that point you would want to be somewhere else.
I don’t think anyone has addresses this. At just about the same time as the dino-killer asteroid impacted, there was a lot of volcanic activity in the Deccan Traps, in India, nearly on the opposite side of the world. There’s some speculation (though I don’t think anything definitive yet) that this was triggered by the shock waves from the impact.
Right. But a well-equipped habitat deep underground (say, bored into the side of a large mountain) should be safe unless close to the impact site.
Which undermines the argument that we should put a settlement on Mars in case Earth is destroyed. Building a dozen or so deep shelters on Earth, each holding, say, a thousand people (who could certainly rotate in and out) would be a way to comfortably survive the worst impacts we know of during at least the past 100 million years, at a tiny fraction of the cost and risk of the Mars option.
I agree that Earth shelters beat Mars ones for practicality given current tech.
It’s not clear to me how long and severe the ecological disaster was post-Chicxulub. There’s a big difference in practicality between needing to store food ahead for 5 years versus needing to provide underground agriculture capability for a few decades or centuries.
An interesting SF story on a related topic is Seveneves: Stephenson, Neal: 9780062334510: Amazon.com: Books . Without revealing too much plot … In the near future versus today the surface of the Earth is comprehensively destroyed after a couple of years warning of the impending inevitable doom. A tiny fraction of humanity survives in orbit for thousands of years. While working to terraform the planet back into habitability. The story ends as they begin to recolonize the surface.
It’s a darn good story well told. The science is pretty solid, but the real story is about how society and individuals adapt to the decidedly weird situation they encounter. Which would be equally applicable to hiding underground as it would be to hiding on Mars or in Earth orbit.
Awesome video, but doesn’t seem to take into account the massive gravitational effects this would have. And since the Space Station isn’t entirely outside the atmosphere, the orbit wouldn’t last long, either.
As far as the implied question “How likely is it for us to look up in the 21st Century and say, ‘It’s a bird! It’s a plane! It’s an asteroid! {splat}’?”, not very likely for very large objects. Astronomers are always scanning the heavens for new stuff, and the orbits of most old stuff is known and calculated long in advance. Only a small, rogue object – that is, a non-orbiting one that came from outside the Solar System on its first visit – would be unknown until the last minute.