Imagine there was another Earthlike planet in our system

[Dannyalcatraz]

That depends on the size of the rock. The dinosaur-killer wasn't that big in asteroid terms. Deorbit about six of them from the asteroid belt on to Mars and you'll do the trick.

The Dino killer- last estimate I saw- was at least 2.5 miles across. That is many, many times the mass of something we could move right now or in the foreseeable. future with anything resembling alacrity or accuracy. Deorbiting and targeting 6 such asteroids would literally be the most massive undertaking in human history up to that point.

(And, as pointed out, it would be easier for hem than for us...)

A bioweapon, in contrast, could be delivered with what we have now. Plus, as I pointed out, post-conquest cleanup would be a cakewalk compared to that caused by an artificial meteor shower capable if exterminating an advanced civilization.

And there are solid reasons NOT to use nukes or asteroids. Just because they are as technologically advanced as we are- as per the discussion's parameters- it does not follow that our scientific discoveries are identical. They could have alloys we don't. They may have a better understanding of astrophysics or chemistry or quantum mechanics than we do.

Use a mass drop or nukes, and all that knowledge is lost.

 

[Derren]

A bioweapon, in contrast, could be delivered with what we have now. Plus, as I pointed out, post-conquest cleanup would be a cakewalk compared to that caused by an artificial meteor shower capable if exterminating an advanced civilization.

Manufacturing such a weapon would be pretty much impossible as we do not even have samples of their DNA and viruses we could upgrade.

 

[Dannyalcatraz]

Manufacturing such a weapon would be pretty much impossible as we do not even have samples of their DNA and viruses we could upgrade.

I was assuming that there had been some kind of contact preceding the decision to initiate genocide, clearly.

...even if that contact were limited to sending interplanetary craft to do "orifice probes" on individuals isolated from their fellow beings...

 

[Morrus]

Like I said; we can't do it.

And nukes? Seriously? I know they sound scary and can destroy cities on Earth. But the rockets ain't the same things as the ones that go to Mars. I don't think folks are grasping that the hard part about sending stuff to Mars is the fuel costs. Hell, it's hard to send stuff around the world in one shot. Mars is a long way away. A long, long way away. Not like Russia-away. Not like the Moon-away. Tens of thousand of times that, with current travel times being 6-9 months or so, depending how far away Mars is (outside that window we just don't send stuff, as it would take years).

 

[Umbran]

But we did build up the capabilities to do it, just in case. The same logic applies.

Except that it was a case where no defense existed, so the best offense became the defense. And that seemed okay, because it might have been possible to sneak up on the bad guy.

That doesn't apply here. We are talking about months to years between when they launch a weapon, and when it reaches the target. My scenario, while sneaky, may call for a decade or more between launch and delivery. There is no "take 'em out quick before they can get us!

The problem is that they are still alien. They think completely different than any human which makes understanding them very hard.

Are you sure? If they have physical bodies, breathe something, use tools, and all, we have lots of points of commonality. We're talking about a species that knows a lot of chemistry (you need that, to launch rockets). They know math and physics. These things are the same on Earth and Mars. There is a constant between us - the Universe! We are interacting with the same Universe, using the same techniques! That implies some significant commonalities.

We don't even know if they have the same needs, emotions or even senses.

Actually, we do. As I said, the Universe is the same here and there. Physics dictates there are only so many ways to perceive your environment.

So no reason to not flatten them in a theoretical attack.

I've raised the reason several times: cost with no return on investment. Oh, and the fact that, really, you can be sure a whole lot of humans are *not* going to like the idea that you're going to commit genocide.

 

[GSHamster]

It's probable that neither side would be able to conquer the other's planet. There's simply too many defenders (6 billion) and it would cost way too much to send an invasion force capable of holding territory.

That being said, there's still something worth fighting for: the rest of the solar system.

The asteroids, Jupiter's moons, all the other planets, all of that is up for grabs. I think the situation would more closely match the European powers rushing to colonize other continents. So the war for the most part would more like the Age of Sail, with privateers and navy ships preying on the colonies and the resources being extracted.

That of course could lead to each side developing weapons capable of destroying the other planet. Not to conquer, but to eliminate a rival claimant for the rest of the system. I doubt these would be used, but it could be a Cold War standoff again.

 

[Umbran]

The Dino killer- last estimate I saw- was at least 2.5 miles across. That is many, many times the mass of something we could move right now or in the foreseeable. future with anything resembling alacrity or accuracy.

See my previous note on how to destroy a civilization economically. If you're willing to take your time, it isn't that expensive, and it is near-current tech. There are many variables, but peaking very broadly:

A 100m diameter stony asteroid would hit like the Tunguska event. 10 to 15 megatons, roughly 1,000 times more powerful than the Hiroshima bomb.
A 350m to a half-kilometer diameter asteroid would hit well beyond any weapon ever created by man. Expect immediate casualties of 10 million or more if it hit today's Earth. Also expect some global climate impact. Given that killing only a couple thousand people in one blow in NYC did severe damage to our economy, something this size is apt to topple governments, if not worse.
A 1km diameter rock does enough to, say, wipe out *all* coastlines of the ocean it hits. It obliterates an entire country in one shot. It throws up enough dust to ensure global climate change. This is enough to kill a civilization.
A 10km rock is an extinction-level event. It kills much of life on the planet.

(And, as pointed out, it would be easier for hem than for us...)

Not by that much. We both probably have to go to the asteroid belt to get the rock. We're firing from the same place...

A bioweapon, in contrast, could be delivered with what we have now.

Yes, but you don't have the ability to test enough to know with certainty that it is virulent and lethal enough to take down the civilization. And, if it doesn't, they're *pissed*.

Plus, as I pointed out, post-conquest cleanup would be a cakewalk compared to that caused by an artificial meteor shower capable if exterminating an advanced civilization.

That is true. The bioweapon designed for them doesn't do diddly to us.

 

[Dannyalcatraz]

See my previous note on how to destroy a civilization economically. If you're willing to take your time, it isn't that expensive, and it is near-current tech.

Taking time isn't really an option. If they're as smart as we are, they will be as aware of the appearance of asteroids on unnatural trajectories as we would be, and would probably react properly- with extreme aggression and an eye towards retaliation.*

In addition, if you want to thoroughly destroy a civilization as advanced as ours, targeting cities won't do it. Our species is concentrated in cities, to be sure, but there are enough of us in rural areas- and at least as importantly, in mobile weapon platforms at sea**- that if you have any designs on landing on the planet after the meteoric bombardment, you have to go for complete annihilation. So the 10km rock or its aggregate equivalent is your only choice.

So once you've triggered the ELE on Mars, how long before the planet's environs are sufficiently restabilized for us to venture down and seize our spoils?

And how much of the valuable knowledge and valuable materials- those created naturally as a byproduct of the metabolisms of living creatures as well as those artificially created by the minds of the decimated- would be eradicated in an orbital mass bombardment?

If the aggressors had any plans to make use of the conqured world within a nation-state's lifetime, a bio weapon is really the best solution.

Testing it would surely be a problem, but not insurmountable. And in all honesty, if this were to be a global effort, it is highly probable the would be multiple teams at work on the same task. It is likely, then, that by the time the drums of war had reached crescendo, not one, but several bioweapons would be deployable.

Given their compactness, it is conceivable that all could be delivered with only a couple of launch vehicles.

As things stand on this planet, we have trouble dealing with one super-bug epidemic at a time. How would our alien targets fare against the release of the equivalent of the 1918 flu, the Black Death, smallpox, anthrax and Ebola being released on their civilization simultaneously?

Assume, arguendo, that this attack were planned post-first contact. As I suggested- drawing from history- such an attack could be as simple as delivering innocuous trade goods via our (possibly unknowingly complicit) goodwill ambassadors. Imagine the engineered plagues' vectorization as our diplomats visited all of the major population centers...





* assuming your target is at least as nasty as we are is a necessity. If they're pacifists, well, they're S.O.L.

** Mars may not have seas, but it is not inconceivable that any intelligent life on that planet may actually be at least partially if not wholly subterranean.

 

[Umbran]

Taking time isn't really an option. If they're as smart as we are, they will be as aware of the appearance of asteroids on unnatural trajectories as we would be, and would probably react properly- with extreme aggression and an eye towards retaliation.*

They'd be as aware... and as incapable of doing anything about it! The interesting part of this trick is that, if you've done your job properly, they don't know you've done it. They know there's an asteroid coming their way, but they don't know you put it there.

But, if you want it to be fast, we can cut the time by an order of magnitude or so. Instead of deploying a solar sail, you slap an Orion drive on the thing. Use up the atomic weapons folks are so keen to use, but to greater effect. Of course, here the fact that you're sending a rock to kill them becomes obvious.

In addition, if you want to thoroughly destroy a civilization as advanced as ours, targeting cities won't do it. Our species is concentrated in cities, to be sure, but there are enough of us in rural areas- and at least as importantly, in mobile weapon platforms at sea**- that if you have any designs on landing on the planet after the meteoric bombardment, you have to go for complete annihilation. So the 10km rock or its aggregate equivalent is your only choice.

I don't believe you need to have an extinction level event to kill the civilization, as far as being an interplanetary-power is concerned.

And how much of the valuable knowledge and valuable materials- those created naturally as a byproduct of the metabolisms of living creatures as well as those artificially created by the minds of the decimated- would be eradicated in an orbital mass bombardment?

I asked at the start - eliminating the civilization cheaply was the *only* consideration?

If the aggressors had any plans to make use of the conqured world within a nation-state's lifetime, a bio weapon is really the best solution.

Testing it would surely be a problem, but not insurmountable. And in all honesty, if this were to be a global effort, it is highly probable the would be multiple teams at work on the same task.

The teams are irrelevant. You don't have the test subjects. You don't have a pack of Martians you can test the thing on!

As things stand on this planet, we have trouble dealing with one super-bug epidemic at a time. How would our alien targets fare against the release of the equivalent of the 1918 flu, the Black Death, smallpox, anthrax and Ebola being released on their civilization simultaneously?

Oh, so now you want to develop several bio-weapons, based in non-terrestrial biology, again without test subjects?

** Mars may not have seas, but it is not inconceivable that any intelligent life on that planet may actually be at least partially if not wholly subterranean.

We are stipulated it is "Earth like". Seas are, I think, a reasonable assumption. Not necessary, but reasonable.

 

[Dannyalcatraz]

They'd be as aware... and as incapable of doing anything about it! The interesting part of this trick is that, if you've done your job properly, they don't know you've done it. They know there's an asteroid coming their way, but they don't know you put it there.

If we are assuming they're as advanced as we are, it is reasonable- no, necessary- to assume that they would be just as capable of moving asteroids as we are.

If we can move in on target, they can potentially move it back off target as a countermeasure. Assuming otherwise could have disastrous consequences, including the Martians redirecting the asteroid to a hit a target on Earth, so any competent battle strategist will have to include that possibility.

As for figuring out the whodunit...well, if the Martians are similar in thought process to humans, its not a question of would any of them suspect Terran treachery, but rather how many and do they have the ability to convince their fellows of their suspicions.

The teams are irrelevant. You don't have the test subjects. You don't have a pack of Martians you can test the thing on!

<edit>

Oh, so now you want to develop several bio-weapons, based in non-terrestrial biology, again without test subjects?

As I said, a bioweapons program presupposes there has been some kind of study of the biology of the target, even if its just the of the old Sci-Fi horror show trope of ships dropping out of the sky to abduct the unsuspecting for "probulation."