A Side Affect of Planetary Bombardment

Loren Pechtel wrote:And note the problem with pushing it with ships--you just push right through it. If a wedge can survive such an impact it would be destroyed--but if a wedge can survive that starships pose an extreme threat to planets and wouldn't be allowed anywhere near them.

Well you probably would drag it with a tractor beam, rather than pushing (although there is a presser mode also). But you still can have the problem of it tearing to pieces, unless you can spread the beam over the entire object to minimize internal stresses.

PS: Small wedge missiles do operate in the atmosphere, but I do not think the larger ships (once wedges get into the kilometer range) do.

Jonathan_S wrote:Obviously if it was aimed through the dead center of the planet then you'd need to deflecting it somewhat over one planetary radius in any direction to cause a miss.

However, not all vectors of acceleration you could apply to the rock will result in the same amount of lateral deflection per newton of applied force. So are more efficient than others.

Let's start with something obvious. The rock is on a ballistic course calculated to reach a point on the planet's orbit at the same time the planet does.

The timing component is important. Because the planet is also moving in its orbit, the intercept is not just a zero-distance problem. It must be at the place the planet will be at the same time as the planet. Therefore, you can play with both components: deflecting one planetary radius and changing the timing. But after running the math, you can actually ignore the timing.

Deflecting in space is a rather easy calculation: just impart the necessary Δv for the remaining flight time and it misses. This is a 2D problem on the plane perpendicular to the current velocity vector and any of those directions is equal to any other. If you have exactly 30 minutes before impact with Earth, you'd need to either deflect 6713 km in any direction. 6713 / 1800 = 3.54 km/s, or 3.93 m/s² (less than half g). If you have double the time, you'd need half the Δv, which means a quarter of the acceleration.

The timing one is different: you can advance or retard the arrival time by accelerating the object in the orbital radius direction. This is a 1D problem. For the same 30-minute scenario with Earth, you need to make it arrive 213.9 seconds earlier or later, or 4043 km/s and 3184 km/s respectively for early and later arrivals. That's a much higher acceleration. The Δv reduction with time is not linear: if you double the time, you reduce the Δv to 1893 and 1681 km/s (less than half); 10x the time and it's 360 and 352 km/s (more than a tenth), etc. This is due to the huge base velocity, much greater than the orbital velocity.

So this is indeed a 2D problem... just not on the plane I thought yesterday.

But you could calculate a wide range of other courses where you adjust the rock's speed and the correct its trajectory in order to meet the planet at a different point and time in its orbit.

You only get a single chance per rock. At 0.1c, it has a velocity much higher than the escape one, so it will cross the orbit of the planet once, or at worst exactly twice if it is directly on the ecliptic. But because its velocity is much higher than the orbital velocity, that second crossing will be much earlier than the planet. There's no orbit closing to the star that would send it back towards the planet that doesn't involve the rock boiling over or even diving into the corona.

The closer your deflection vector is to one of those alternate intercept courses the less the rocks point of impact will shift for a given acceleration. So you'd want to apply acceleration in an efficient direction. I suspect that any direction direction perpendicular to the current vector would be pretty close to optimal. (But fortunately you don't need to actually work one of those optimal vectors out by eye, or longhand, that's what computers are for -- or just apply enough brute force that it doesn't matter if you're inefficient about it )

Yep, see Math above.

Oh, there's a problem with the 30 minute figure.

If you have 30 minutes after someone has landed on the rock and installed the rockets, you're fine. If they have landed but haven't installed the rockets, the issue will be how long they can do so.

But if it's colliding 30 minutes after detection, you're screwed. To emplace a rocket, you need someone to zero-zero with the rock. It takes a LAC at 750 gravities nearly 68 minutes to accelerate to 0.1c and such a ship would need to be in the right position to intercept, 61 million km from the interception point.

So if your solution requires a zero-zero rendezvous, you need to detect it at least 2 hours before impact. If it's tighter than that, then you'll need alternate solutions. You can shoot it with a very large rail gun to break it up into smaller chunks that you can destroy with wedges, or boiling a side of it with a laser so the ejecta works as a rocket. Or just run over the entire thing with a wedge: what have you got to lose if that doesn't work?

Fortunately, a 2-hour detection is doable. At 0.1c, that's 12 light-minutes, which happens to be the distance between Manticore and the hyperlimit, and more than the distance to Manticore-A. Ditto for Earth; the detection would be between the orbit of Mars and the inner edge of the asteroid belt (if it were on the ecliptic).

Loren Pechtel wrote:

Jonathan_S wrote:The closer your deflection vector is to one of those alternate intercept courses the less the rocks point of impact will shift for a given acceleration. So you'd want to apply acceleration in an efficient direction. I suspect that any direction direction perpendicular to the current vector would be pretty close to optimal. (But fortunately you don't need to actually work one of those optimal vectors out by eye, or longhand, that's what computers are for -- or just apply enough brute force that it doesn't matter if you're inefficient about it )

I don't think any of those alternate intercepts are close enough to the target trajectory to matter.

Well there are and infinite number of them And so many of those wouldn't be so very different from the target trajectory.

The Earth's mean orbital speed around the sun is about 30 km/s. (And it's 12,742 km wide). So let's assume, simplest case, that the rock is crossing perpendicular through Earth's orbit -- that means if you make the rock arrive 5 minutes earlier, and nothing else changes, and it'll pass about (300s * 30 km/s - 6,400 km) 2,600 km ahead of the edge of the Earth* -- hitting the same point in Earth's orbit just 86 seconds before Earth starts crossing it. So only a slight nudge could cause it to still impact. (FWIW it takes the Earth about 7 minutes to fully cross any given point in its orbit -- 12,742 km / 30 km/s ~= 425 seconds)

Make it cross Earth's orbit 1 hour earlier and it'd pass about 101,000 km ahead of the Earth; but apply a bit of the correct side vector and now it'll hit the Earth about an hour earlier (and, due to Earth's rotation, likely about 1,600 km further east).

Similarly if you decelerated to cross the orbit an hour later you'd need to shove it the other way. And for every second of those two hours (or any other length of time) there's a corresponding deflection along the Earth's orbital track that would cause it to still impact the Earth.

(Okay, technically, I think that gets trickier if you need to fly past the sun to hit it; because now you need to worry about staying far enough away it doesn't tear your rock apart and adjust for how much its gravity will deflect your trajectory. So on some approaches being 4-8 months earlier or later might be an issue)



Fortunately for Earth there's a far larger infinity of courses that don't lead to an impact -- so even picking your deflection by pure chance you'd be far more likely to cause it to miss than to cause it to impact at a different time.

(Adjust numbers as necessary for the size and orbital velocity of the planet in question)
---
* I'm neglecting the diameter of the rock itself; but hopefully it's small enough not to be a major factor.

I would have expected a lot more energy than only 10% of the dinosaur killer because it would be traveling significantly faster. And I also think it would depend on where it hit. If it hits right on a major fault line it could wreak enormous havoc and cost lots of lives and damage to infrastructure. It could hit in the ocean and cause major tsunamis.

ghazestor wrote:I would have expected a lot more energy than only 10% of the dinosaur killer because it would be traveling significantly faster. And I also think it would depend on where it hit. If it hits right on a major fault line it could wreak enormous havoc and cost lots of lives and damage to infrastructure. It could hit in the ocean and cause major tsunamis.

Everyone also forgets the opposing shock impact - the shock energy hits with so much force, it causes a bulge out the other side of the planet. If you look at the opposite side of the planet from Chicxulub, you will find an area of the seafloor that look like a giant scab - risen and broken apart, with the layers upended.

So even if you were on the opposite side of the planet, the force of the impact would set off a 2nd tsunami/seismic event which could endanger you.

Theemile wrote:

ghazestor wrote:I would have expected a lot more energy than only 10% of the dinosaur killer because it would be traveling significantly faster. And I also think it would depend on where it hit. If it hits right on a major fault line it could wreak enormous havoc and cost lots of lives and damage to infrastructure. It could hit in the ocean and cause major tsunamis.

Everyone also forgets the opposing shock impact - the shock energy hits with so much force, it causes a bulge out the other side of the planet. If you look at the opposite side of the planet from Chicxulub, you will find an area of the seafloor that look like a giant scab - risen and broken apart, with the layers upended.

So even if you were on the opposite side of the planet, the force of the impact would set off a 2nd tsunami/seismic event which could endanger you.

Really? Exactly where is this? Most of the oceanic floor that existed at the end of the Cretaceous is long gone, swallowed by trenches. The biggest piece of oceanic crust that has survived is currently in the North Pacific, being fed into the Izu–Bonin–Mariana trenches.

Robert_A_Woodward wrote:

Theemile wrote:
Everyone also forgets the opposing shock impact - the shock energy hits with so much force, it causes a bulge out the other side of the planet. If you look at the opposite side of the planet from Chicxulub, you will find an area of the seafloor that look like a giant scab - risen and broken apart, with the layers upended.

So even if you were on the opposite side of the planet, the force of the impact would set off a 2nd tsunami/seismic event which could endanger you.

Really? Exactly where is this? Most of the oceanic floor that existed at the end of the Cretaceous is long gone, swallowed by trenches. The biggest piece of oceanic crust that has survived is currently in the North Pacific, being fed into the Izu–Bonin–Mariana trenches.

I don't remember exactly where - I saw a documentary about 10 years go where they were running a simulation of the impactor where the outcome showed the far side of the earth distorting from the impact, which completely surprised the geologists. they looked where the models predicted and there was a geologic anomaly there under water. I was expecting the location to the the Siberian volcanic traps, which started erupting "shortly" after the Chicxulub impact - but no direct relation (other than the entire globe would have been flexing from the impact, and popping at the seams.)

Theemile wrote:Everyone also forgets the opposing shock impact - the shock energy hits with so much force, it causes a bulge out the other side of the planet. If you look at the opposite side of the planet from Chicxulub, you will find an area of the seafloor that look like a giant scab - risen and broken apart, with the layers upended.

So even if you were on the opposite side of the planet, the force of the impact would set off a 2nd tsunami/seismic event which could endanger you.

Robert_A_Woodward wrote:Really? Exactly where is this? Most of the oceanic floor that existed at the end of the Cretaceous is long gone, swallowed by trenches. The biggest piece of oceanic crust that has survived is currently in the North Pacific, being fed into the Izu–Bonin–Mariana trenches.

Theemile wrote:I don't remember exactly where - I saw a documentary about 10 years go where they were running a simulation of the impactor where the outcome showed the far side of the earth distorting from the impact, which completely surprised the geologists. they looked where the models predicted and there was a geologic anomaly there under water. I was expecting the location to the the Siberian volcanic traps, which started erupting "shortly" after the Chicxulub impact - but no direct relation (other than the entire globe would have been flexing from the impact, and popping at the seams.)

After only a brief search I did not find the reference you mentioned, but I did find this speculative video on Youtube. There are articles suggesting earthquakes and tsunamis at the antipode of the Chicxulub impact, but I did not see anything more definite on it. Note that the antipode of the dinosaur killer is not in Siberia, but seems to be off Australia; also that event was about 66 million years ago, not the 250 million when the Siberian Traps event occurred. The event you meant was the Deccan Traps in India.

Asteroid Impacts Cause Volcanoes to Erupt on the Opposite Side of the Planet

The worst mass extinction event on the planet, called the Permian Triassic extinction event, was caused by the eruption of several million cubic kilometers of lava at the Siberian Traps. However, these volcanoes may have an unexpected origin, an asteroid impact. On the exact opposite side of the planet, the large Wilkes Land Crater exists right at the antipode of where the Siberian Traps began. This video will discuss the theory that certain flood basalt volcanoes originated from large asteroid or comet impacts.

Theemile wrote:I don't remember exactly where - I saw a documentary about 10 years go where they were running a simulation of the impactor where the outcome showed the far side of the earth distorting from the impact, which completely surprised the geologists. they looked where the models predicted and there was a geologic anomaly there under water. I was expecting the location to the the Siberian volcanic traps, which started erupting "shortly" after the Chicxulub impact - but no direct relation (other than the entire globe would have been flexing from the impact, and popping at the seams.)

Very interesting! Do you by any chance recall the name of it?