The future. Parts of the solar system are colonized by outposts, but only Mars became a major industrial and economic center.

The Martian stock exchange is the largest in the system and the space port of the martian capital has the largest throughput.

The most active people seeking quick money and innovative businesses settled on Mars. Mars is a hub for asteroid mining and deep space exploration. Mars is the center for biological research and genetic engineering.

Earth is a luxurious place for the rich, the celebrities and the artists. They have villas and castles there, expensive resorts on artificial islands and everything for pleasure and entertaining. Earth is the place where the UN headquarters are located and most of the politics is done there.

Earth still has greater total industrial capacity than Mars but it is politically fragmented. Yet the UN Standards and Intellectual Property Organization imposes its rulings on the whole world the way it is currently done in the EU.

A controversy arose when UN standards body demanded Mars to cease its research in human cloning and other non-ethical experiments as well as infringing upon copyrights.

Mars refused to comply, so Earth imposed economic blockade. Mars is still dependent on many critical things from Earth so they cannot just wait. They threat to make nuclear, biological and ecocidal bombardment of Earth if blockade is not lifted.

The problem with Earth is that they cannot do the same because of deep gravity well of Earth. Mars can launch a lot of self-propelled bombs and put many ships in Earth's orbit. Earth cannot do the same at least at the same amount. They have advanced technology, but no launch capability similar to that of Mars. What they should do?

Moon has a small Earth outpost but nothing serious is there.

  • $\begingroup$ Did you consider that maybe your earth politicians made a huge huge huge mistake in the way they handled the situation? Every war has its losing side. Is there a reason that losing side simply cannot be Earth? Doing a blockade when you don't have the military to back it up is like hitting a hornet's nest with a stick saying "stop stinging me!" $\endgroup$ – Cort Ammon Jan 1 '16 at 20:25
  • $\begingroup$ @Cort Ammon Earth has good military, but the gravity well is a huge disadvantage. It also has greater population overall and many resources Mars does not have. $\endgroup$ – Anixx Jan 1 '16 at 20:26
  • $\begingroup$ If they had a "good military" but failed to account for the laws of physics when deciding military actions like a blockade, we need to better understand what Earth thought "good military" meant. $\endgroup$ – Cort Ammon Jan 1 '16 at 20:29
  • $\begingroup$ @Cort Ammon there was never a space war yet. The militaries of the Earth's countries are intended for wars on Earth. Mars has virtually no military at all, but they can produce it over some time, as they have all necessary technologies, including that for nuclear bombs and biology warfare. $\endgroup$ – Anixx Jan 1 '16 at 20:31
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    $\begingroup$ Related: Could a Mars colony use asteroids as weapons against the earth? and to a lesser extent Planetary defense. We might have some others but those are the ones I can dig out with a quick search. $\endgroup$ – a CVn Jan 1 '16 at 20:41

Many of the assumptions behind the scenario have been examined by others, but let's move ahead and suggest the Martians really mean what they say and are willing to go into a shooting war. This seems insane, but the Japanese Empire made the same calculations after the United States imposed the embargo of oil and steel imports on Japan, and launched the attack on Pearl Harbour which started American involvement in WWII.

This was an enormous gamble, since the United States was at the time the world's largest producer of oil and produced something like 10X the annual steel output of Imperial Japan. The Japanese were seriously outmatched from the beginning, yet believed that a surprise attack might be enough for the Americans to sue for peace. This may be the underlying assumption of the Martians as well.

Since we already have interplanetary travel and commerce, we can assume that Earth has planetary and interplanetary launch capability, as well as a Space Traffic Control System capable of observing the Solar System. When the Martians begin launching ships or weapons towards Earth, it will be highly visible (even mass drivers launching rocks from Mars will have huge heat signatures). If the Martians launch with minimum energy trajectories from Mars, then Earth will have about 180 days before things arrive. Higher energy trajectories will be shorter but even more visible to Earth. To put this in perspective, the Space Shuttle Main Engines could be visible to Earth if fired in the orbit of Neptune, while the Shuttle's manoeuvre engines would be visible from as far away from the asteroid belt.

Given the high velocities of objects in interplanetary orbits, all Earth needs to do is launch "buckets of sand" in intersecting trajectories. All that is needed is a simple carrier filled with sand or ball bearings, and a bursting charge that releases the projectiles in the path of the oncoming weapons. Even small particles will strike with enormous amounts of kinetic energy, and either destroy the incoming projectiles outright, or erode away at the structure and provide impulses to push them off their incoming trajectory. Once the first wave has been hit, the trajectories are re examined and further interceptors can be sent to deal with any leakers, with nuclear pumped warheads for the biggest threats. (Nuclear weapons can drive pellets to 70+km/second, nuclear shaped charges can fire at a fair fraction of the speed of light and nuclear pumped X ray lasers can deliver huge pulses of energy to distant targets).

See http://www.projectrho.com/public_html/rocket/spacegunconvent.php for more details of how nuclear weapons can be used in space.

As for the rest, Earth's economic embargo, combined with very powerful messaging and possibly cyberwarfare to bolix up Martian launch capability and crash their stock market will do the rest. A collapsed Martian economy will take the legitimacy away from the Maritan political class, and Earth can come to the rescue with a "Marshall Plan" to buy the support of the Martian population. (Playing with Martian life support is close to genocide, and leaving life support alone sends a strong signal to the Martians that their political class is endangering them, while the forbearance of Earth keeps them alive).

So long as the Earth's political goals in the war are essentially defensive in nature, then they should be able to defend themselves very well, and win the war with a low cost in blood and treasure.


Mars refused to comply, so Earth imposed economic blockade. Mars is still dependent on many critical things from Earth so they cannot just wait. They threat to make nuclear, biological and ecocidal bombardment of Earth if blockade is not lifted.

Even ignoring the events that led up to the blockade, this is where what you describe gets outright surreal. Let's outline the sequence of events, in the orbital-altitude level of detail:

  • Mars is totally dependent on Earth.
  • Mars angers Earth.
  • Earth institutes a blockade against Mars to force Mars to comply with Earth's demands.
  • In response, Mars goes to war against Earth, in a way that is virtually guaranteed to cause massive damage to Earth's biosphere and population.
  • Mars expects that after such a threat, Mars and Earth can just go back to being old-time buddies again.

The old saying goes you don't bite the hand that feeds you. There is a lot of truth to that here, simply because of the total dependence of the people on Mars on the good will of the people on Earth.

Dropping massive amounts of nuclear weapons on the people that you want help from seems to me like, very generally speaking, a not particularly great long-term strategy. In fact, it sounds like a lousy short-term strategy as well.

As for your actual question, how Earth could defend itself in this scenario. Well, we have two main options. We can't really move the Earth out of the way, but there are the installations on the Moon (which could, at least in theory, be pressed into service as a launch platform, taking advantage of the Moon's shallower gravity well if the material is already there; we gain no advantage if we have to transport materials there first), and there is the option of launching something from Earth.

For completeness' sake, the Moon's gravity well (at 2.38 km/s escape velocity) is far shallower than either Earth's (11.2 km/s) or Mars' (5.03 km/s). Those of you reading this who don't know why this is a big deal, keep in mind the tyranny of the exponential nature of the rocket equation. It's not a perfect comparison, but you could compare even something like the Falcon 9 with the Apollo Lunar Module, specifically the ascent stage.

In an unpowered transfer orbit, which is the best you can hope for if you basically hurl "barrels of pollutant or dangerous bacteria" at another solar system body, it's not like the weapons are doing a lot of maneuvering. Rather, they are going to be coasting along at likely some small above-parity fraction of the origin body escape velocity, along an orbit that can be trivially calculated. Even at closest approach, Mars is a minimum of about 55.8 million km away; at 6 km/s, even if you could go in a straight line (which you cannot), even that would be a 108 Earth days trip.

The obvious option is a powered interceptor. This would be akin to New Horizons, only far easier to pull off (and probably needing a bit more fuel for maneuvering, but far less to get it onto an appropriate transfer/intercept orbit). Earth has at the very least months, and more likely 1-2 years, of lead time before the impact. A small nudge (at a guess, meters per second of delta-v could be plenty, if applied early enough) could disrupt the transfer orbit sufficiently that the weapon misses the Earth and potentially hits Mars instead.

An alternative approach would be to send something that makes a sufficient boom (which need not be a large one) to damage the weapon containment vessel. That would either cause the outright destruction of the weapon, or leaking of its dangerous substances into space over time, where they would be essentially harmless. Earth would still potentially have to deal with the impact in the latter case, but it would be less of a problem (and it's much more likely that atmospheric reentry would take care of it, then).

A third possibility is that the people on Mars would need some way of preventing a disaster on Earth if the conflict ends while the weapon is in a transfer orbit. Figure out the specifics of that process and replicate it, or bring out a large wrench.


Do some investigation into who screwed up, and either fire your diplomats or your military advisers. Then go make your diplomatic team go into high gear.

Somebody sold you on the idea that a blockade was not dumb. That person was simply wrong. How do we know? Well, Mars decided to threaten you with a nuclear war that you cannot win.

If your military advisers were not idiots, they would have figured out that maybe you should have to be ready to defend yourself against the single largest threat you have ever dealt with: another planet. Presumably, they bothered to note that Earth was basically in a lost position in a war with Mars. If they didn't arrive at this conclusion, they either know far more than we've been given in the question about Earth's classified military projects, or were idiots who shouldn't have graduated from the military academy. If you are a top brass and can be caught with your pants down with, "Gee. Ain't that quaint. Mars can utterly obliterate us at any point in time and we can't do a thing about it because our 'good military' just can't compete when Mars has the high ground (literally speaking, from the gravity wells)," frankly, you deserve the flogging you're going to get.

If the military advisers did their job, then the Earth governments know just how weak their position is, and how utterly and completely dependent they are on diplomacy. Every diplomat should have been notified: "by the way, any Naval Academy graduate can figure out that we lose any war with Mars we fight. This would be a good time to not make diplomatic decisions that risk war." I'll presume this happened. Military advisers aren't that bad at their job.

The diplomat's job was to keep things in balance. Mars needed to be dependent enough on Earth's resources to ensure they don't want to upset Earth, but not so dependent on them that they're ready to take over Earth using their massively superior military strength. That was their job. It didn't happen. Fire them, get new diplomats. These new diplomats need to restore that balance. It's probably going to take some concessions, given that we were stupid enough to actually take a military solution (blockade) against a force that can win the war at any time, just by bothering to enter the war.

Meanwhile, you should probably talk to your politicians. Explain to them that it is not acceptable for a politician to have to ask questions analogous to "I just punched a grizzly bear in the nose, and its angry at me. I have no tools and no weapons that can hurt them. How can I kill the grizzley?" Sometimes you eat the bear, sometimes the bear eats you. When you forget to actually assess your strategic position before entering the war, the bear eats you more often than not.

  • $\begingroup$ Is not the situation discribed actually what is expected to be in the future if colonization of Mars inevitable? Having less gravity well allows them to terrorize Earth even having less military/economic power. $\endgroup$ – Anixx Jan 1 '16 at 21:59
  • $\begingroup$ "I have no tools and no weapons that can hurt them." - okay. bat Earth has time. What kind of weapons they should develop for a successful war with Mars? $\endgroup$ – Anixx Jan 1 '16 at 22:00
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    $\begingroup$ With the way you are setting it up, you're going to find that finding a "winning" strategy is really hard to come by. You've intentionally set up a diplomatic nightmare, a military that basically has ignored reality for decades or worse, and a bunch of politicians dumb enough to ignore all of that and still try to get their way. I think the darker truth is "any planet willing to carpet bomb another planet with nukes has the first strike advantage." There's a reason we really hate first-strike nukes in our civilization today. $\endgroup$ – Cort Ammon Jan 1 '16 at 22:15
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    $\begingroup$ @CortAmmon Your analysis is wrong. War is already over, Earth won. Mars it stated to be dependant on Earth. If Martian survival depends on Earth, they are the ones that are detached from reality. To acquire what they need, Martians don't need to just beat Earth. They need to OCCUPY Earth. With lower industrial base, population and limited resources it's impossible. Strategically speaking it's not "13 colonies vs Britain", it's "Japan vs USA". $\endgroup$ – M i ech Jan 1 '16 at 22:37
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    $\begingroup$ @user16614 I guess that depends on how well Mars's military analysts have been keeping track of things, and stockpiling properly. Its possible that you're right that mars may have already lost. However, that doesn't mean Earth wins. It just means that Mars no longer has anything to lose. We don't know enough to actually tell which way it is, so you very well might be right. $\endgroup$ – Cort Ammon Jan 1 '16 at 23:17

As Thucydides pointed out, all Earth has to do is shoot sand/rocks/ball bearings at any incoming missile or bomb to knock it out.

A 1cm chunk of metal traveling at hundreds of meters a second isn't going to slow down much for the shell of a missile.

This is the idea behind the Brilliant Pebbles ICBM defense program.
It would work out just as well against any interplanetary missiles.

The real threat from Mars isn't missiles and bombs, but dark radar absorbing dumb rocks.
Take your average small to medium sized asteroid, coat it in something that absorbs radar, paint it black to absorb light, and boost it toward earth.

Even if the defenses see one coming, a solid chunk of rock isn't going to mind being hit by a ball bearing, and it'll have enough kinetic energy to rival any bomb. It would probably only take a couple to start a nuclear winter and destroy most of the life on Earth.

If Mars were to time it so that the first hit the middle of the ocean the tidal waves would do a lot of damage and get Earth's attention without throwing as much dust in the air that would probably be better.


As stated, the situation doesn't make a lot of sense. Just what is it that Earth exports to Mars that is so critical? And what is it that Mars exports to Earth that is worth the trade? If the Martian stock exchange is the largest in the solar system, this would suggest that inter-colony trade dwarfs Earth's export capacity, and Earth would seem to be largely irrelevant to the economy of the Outer Planets.

And this seems odd in itself, given that there is no Lunar economy to speak of. The moon is enormous compared to the asteroids, and the failure to develop the moon's potential suggests that the asteroids are not going to do well. After all, the lunar surface has many of the same challenges: vacuum and radiation. Lunar gravity is so low that it will take some hand-waving to justify the benefits of zero-g to be overwhelming - and for industrial processes a complete lack of gravity may well be a handicap.

To a large degree this is a Mexican Standoff. The Martians cannot preemptively destroy Earth's launch capabilities: if they do, they have made the embargo permanent and irrevocable. That is, they lose. The Martians cannot pose an existential threat to earth without committing suicide. What they can do is play politics: threaten damage to some governments so they will put political pressure on the others to drop the embargo. Since presumably it's the rich, powerful nations which do the space launches, this risks triggering a series of wars by the rich nations which would result in a politically unified Earth which is willing to really stick it to the Martians.

  • $\begingroup$ The one essential element that Earth can provide the Solar System is phosphorus, which is essential for all life. $\endgroup$ – Thucydides Jan 3 '16 at 15:22
  • $\begingroup$ @Thucydides - Phosphorous is widely available in Martian rocks and soils. www.lpi.usra.edu/meetings/7thmars2007/pdf/3228.pdf. Furthermore, all extraterrestrial biosystems need to be closed (or very close to it) so virtually all phosphorous would be recycled. $\endgroup$ – WhatRoughBeast Jan 3 '16 at 17:25

You are drawing parallels between American conflict of Independence, which is wrong. 13 colonies were not dependant on Great Britain. Severing trade wouldn't cripple or outright kill american colonists, moreover they rebelled BECAUSE Britain tried to force them to buy imported goods despite either own manufacturing capacity or lack of need for them.

From strategic standpoint it's like WW2 Japan vs USA. Japan had fuel, ammo and other resources only for few months of war and they knew it (Japanese Isles are rather infamous for their lack of natural resources). They also knew that sooner or later they will come into conflict with USA, thus they went for shock tactics and proverbial jugular, hoping to cripple Americans before they bother to mobilise. It worked to an extent, Japan got enough breathing room and position strong enough to last over 3 years, instead of 3 months.

And this answers your question: Earth doesn't need to win. They need to outlast Mars. You said that Mars is dependant on Earth for critical resources, as soon as elements/parts/whatever start running out, they are crippled or dead. But dropping nukes doesn't solve their problems. They need to occupy manufacturing facilities, control them and ship whatever they need back to Mars. In other words: they need to beat Earth military. On Earth orbit. On Earthen soil. It's as if American Colonies needed to send their Minutemen back to Europe to take Buckingham Palace in order to survive at all. Threat of Nuclear or Biological warfare doesn't give them what they want. If they bomb Earth, they gain nothing, they still need to take what they need while Earth can just deny it by destroying critical facilities. At best, Martians die, at worst, it's MAD.


Well, here is what each side needs to do in order to win:

For Mars to win, it needs to destroy Earth's military capabilities, and essentially leave Earth without the ability to strike back. It needs to do this very quickly. If Mars simply tries to wipe out all life on Earth, or greatly damage Earth, then Mars is basically committing suicide. It needs to make Earth settle for a negotiated peace, fast.

For Earth to win, it needs to stop Mars from destroying its military forces, and leave itself capable of inflicting massive retaliation against the Martians. Earth needs to launch raids against Martian fuel and food storage, to starve the planet and force Mars to capitulate. Either side destroying the other will have serious economic consequences for the victors after the war. Mars may be dependent on Earth, but I believe that I'm fairly safe in assuming that the destruction of the Martian colony will result in a new Great Depression on Earth, at the least.

Mars needs to launch so many projectiles at Earth's military stations, communication centers, and transportation systems, that Earth's military cannot intercept them all, or cannot intercept them all in time. Once they hit, Earth wil, not be able to coordinate its forces, and will lose the capability to inflict massive retaliation. Mars needs to follow this up by offering a very lenient peace settlement to Earth. Hopefully, the shock and disabling of their forces will cause Earth leaders to agree to a negotiated peace, so that everyone can get off as easily as possible.

Earth needs to move everything. They need to make their forces as dispersed and mobile as possible, and/or hide their forces amongst civilian population centers. Hopefully, the Martians will be afraid to target these, since that would make a devastating war inevitable. Earth then needs to launch quick raids against Martian supply depots, to make Mars starve faster. Mars will capitulate at that point.

Earth has the advantage, unless they decide not to use the above plan.


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