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To me it seems surprising, frightening, and sadly typical that before humans set foot on a celestial body, they plan to nuke it (1, 2, 3).

What would a big explosion on Moon or Mars look like?

I suppose that on Moon there would be no mushroom cloud, since it has virtually no atmosphere. Also nothing would burn since there is no oxygen. Would there be any flash? And how about Mars?

Everyday Astronaut
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  • The temperature in a thermonuclear explosion get us to 100,000,000 degrees C, there will certainly be a flash. – GdD Nov 24 '17 at 12:40

2 Answers2

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Nuking the Moon:

If you detonate a nuke on the surface of the moon, it probably wouldn't be as spectacular as a detonation on earth. Most of the energy released in a nuclear blast is in the form of a pressure wave and heat with only a small portion in radiation. If you detonate the bomb above the surface of the moon the explosion would be extremely bright (instantly blinding/destroying unprotected eyes and cameras in the vicinity along with bombarding it's surroundings with other forms of radiation. The infrared emissions would probably make things pretty hot in the surrounding area and if detonated above frozen water, possibly instantaneously vaporize it.

If you detonate on or under the surface of the moon, the effects would probably be similar except that the blast wave would propagate through the mun's surface similar to an earthquake and the bomb would blow a large amount of material away at high speeds. This high speed moon debris would also never slow down until it hits something (probably the moon) and it would be traveling so fast that large pieces would probably be on suborbital trajectories and might even land on the other side of the moon (although it's hard to gauge as there's no exact numbers on how fast objects could be launched by a nuclear explosion in a vacuum. For reference, nuclear shock waves on earth reach up to 0.5km/s and lunar escape velocity is around 2.4km/s.

Nuking Mars:

Assuming we have a nuke that can detonate on Mars, the explosion would probably be similar to one on earth with a couple key differences. Mars' atmosphere is much thinner and is mostly c02 and Mars' gravity is lower. Detonating a nuke on mars would release a large amount of heat into the atmosphere along with shooting debris and creating a shock wave. The "size" of the explosion probably wouldn't be as big as on the earth as the atmosphere is thinner but there would probably still be a mushroom cloud as the atmosphere that is heated up by the explosion would be less dense than the very cold atmosphere of Mars.

Dragongeek
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    "Making conventional explosives go off in a vacuum is surprisingly difficult... it probably wouldn't detonate or it wouldn't detonate properly" Why? Can you support this statement somehow? The supporting information about conventional explosives in space would also be helpful for the question Lunar excavation by blasting - would there be unique challenges, difficulties or safety issues?. – uhoh Nov 24 '17 at 10:06
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    The Saturn V and other rockets used a lot of explosives for stage separation and other tasks. These charges were extreamly reliable, not a single fault in the Apollo programm. – Uwe Nov 24 '17 at 10:34
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    There have been nuclear explosions in space, i.e. in a vacuum. That's a solved problem. – Hobbes Nov 24 '17 at 11:19
  • @Hobbes I'm not saying nukes don't work in space, I'm saying your typical, "off-the-shelf" warhead isn't designed for the temperatures, radiation, and vacuum of space and probably would need to be slightly redesigned before it's safe to use in space. – Dragongeek Nov 24 '17 at 12:04
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    Most current nuclear warheads are designed to be delivered by ICBM, via a trajectory that reaches into space. Those warheads need to be designed for the temperatures, radiation, and vacuum of space anyway. Plus, nuclear warheads can be used for the delivery of an EMP, which is often done by an exoatmospheric explosion. – Hobbes Nov 24 '17 at 12:13
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    I removed the stuff on how it would work, it's not relevant to the question – Dragongeek Nov 24 '17 at 12:57
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To me it seems surprising, frightening, and sadly typical

Bombing the moon was mostly a "just because we can" demonstration of military superiority.

Using nuclear bombs on Mars is the only way we have of creating a planetwide effect without requiring an impossibly large amount of resources.

Would there be any flash?

From the article on the A119 proposed nuclear detonation on the Moon:

If the explosive device detonated on the surface, not in a lunar crater, the flash of explosive light would have been faintly visible to people on earth with their naked eye,

A surface detonation would not result in a mushroom, but there would be a 'cloud' of high-velocity debris.

On Mars, you would get a mushroom, although I suspect it'd be less visible than on Earth due to the lower atmospheric pressure, so less dust gets picked up. A quick search didn't turn up any studies on the effect of a large detonation on Mars.

There have been some reactions by scientists to Musk's plan, citing two major problems:

  • it wouldn't be as quick as Musks hopes
  • the fallout would be a major problem if you hope to make the planet habitable.
Hobbes
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