Feasibility of nuclear detonation for deep planetary science on Mars

[ElfredaCyania]

TL;DR Summary

Questions about nuclear detonation on planets for deep structure science.

Hello everyone,

I'm looking into the use of nuclear detonations for scientific exploration on Mars and similar rocky planets. Currently, our tools for seismic and subsurface research on extraterrestrial bodies primarily include impactors and rover drills. For context, the largest recorded impactor on the moon delivered about 57GJ of energy—comparable to the smallest nuke. The biggest marsquake S1222a delivered up to 708GJ (the biggest marsquake confirmed to be an impactor is around Mag 4 or 63GJ). In contrast, historical nuclear tests on Earth, such as Castle Bravo (63 PJ) and the Tzar (210 PJ) carried significantly higher energy.

Concepts like the NIAC Borebot aim to dig deeper than any nuclear explosion could (~10km ideally) but focus on different scientific objectives without the capability to induce seismic activity like a nuclear detonation would. Impactors have proven valuable for planetary science, yet they are inherently limited by their energy capacity and the extent of data they can generate.

Adding to this, Project A119 offers a real-world reference for such a concept, though it was never executed.

Discussion Points:
Pros and Cons of nuclear detonations (ground burst, underground, or airburst) for deep structure research on Mars?
For pros, I can think of large excavation volumes, high earthquake magnitude, instant data acquisition and shorter mission periods, even a ground observatory could analyze the event remotely.
For cons, besides all sorts of contamination, disruption to ongoing missions, and potential impacts on the operability of Mars' orbit.

Technical Challenges and Mission Design:
I suppose it would be cheaper than sending rovers, but collecting the data is another thing, maybe requiring multiple preparatory missions.

Ideal Locations for Detonation:
Are there specific regions on Mars that would be particularly suitable for such experiments?

NO political and ethical considerations to focus purely on the scientific and technical aspects.

Edit: Assuming no artificially imposed prohibitions(like outer space treaties), risk concerns remain valid, which may be addressed by following a protocol that would resemble the one required for launching the DRACO NTR.

 

[berkeman]

NO political and ethical considerations to focus purely on the scientific and technical aspects.

I'm not sure what this means (maybe like the Star Trek non-interference directive?), but I'm pretty sure that launching a big nuclear weapon on a Mars mission would be a non-starter. If our launch vehicles were 100% reliable, then maybe...

 

[Frabjous]

Here are some books that might give you some ideas.
Nuclear Explosion Seismology by Rodean
Nuclear Explosions and Earthquakes by Bolt
Monitoring Underground Nuclear Explosions by Dahlman and Israelson

 

[ElfredaCyania]

I'm not sure what this means (maybe like the Star Trek non-interference directive?), but I'm pretty sure that launching a big nuclear weapon on a Mars mission would be a non-starter. If our launch vehicles were 100% reliable, then maybe...

For the sake of this question, we could assume no artificially imposed prohibitions(like treaties), but risk concerns remain valid, maybe addressed by following a protocol that would resemble the one required for launching the DRACO NTR rocket.

 

[berkeman]

following a protocol that would resemble the one required for launching the DRACO NTR rocket

Reference link please? Thanks.

 

[ElfredaCyania]

Reference link please? Thanks.

There's no existing protocol for that, but since it's an NTR demonstration scheduled for launch after roughly a decade. It implies that HALUE (Uranium enriched between 5 and 20%) could get into orbit. Besides we are already using more dangerous Pu-238 in space missions.
Estimating the actual safety requirement for launching a nuke will be hard though, but it's not the main point of the question. It's more about detonation's impact on Mars.
DRACO (DARPA), DRACO (NASA)

 

[berkeman]

Besides we are already using more dangerous Pu-238 in space missions.

Reference please? (I know you are new here, but please ALWAYS provide links for technical assertions here. Thank you)

 

[ElfredaCyania]

Reference please? (I know you are new here, but please ALWAYS provide links for technical assertions here. Thank you)

Got it. Pu-238 has been used in RTGs, from 1961 to future missions (GPHS-RTG). While both are alpha emitters, Pu-238 (and a common byproduct Pu-239) is more dangerous than U-235 if inhaled due to a much shorter half-life[1][2]. Although Uranium poses another type of risk known as nuclear proliferation, and it's true the nukes will use Pu239 and U235, H-bombs and later three-stage bombs are mostly powered by fusion material (like stable element Li-6 and Li-7 in Bravo) and U238. Also if you consider only using 10 kg of Pu-239 (this is a bit more than the 8.1 kg used in GPHS-RTG) for a nuke it gives a yield of ~840TJ, much more than any event you could expect from natural impactors, not to mention you could wrap safe material around it to make a H-bomb. But I will not go deeper into the nuke designs since I want to focus on the mission.

 

[berkeman]

Got it. Pu-238 has been used in RTGs, from 1961 to future missions (GPHS-RTG).

Thanks. But what is the ratio of the mass of that Pu in each launch to the launch nuke that you are proposing?

 

[Baluncore]

I'm looking into the use of nuclear detonations for scientific exploration on Mars and similar rocky planets.

The value of the information to science is not worth the investment, nor the liability.

If we need critical information, then we will think of a more subtle way to get that information. If it is buried so deep that we cannot sense it, then there is no need to know.

Nuclear explosions are used by people without critical thinking skills, those who cannot solve problems by thinking rationally, or cannot maintain two models at the one time.

There needs to be some mystery to maintain scientific interest in our universe.

 

[ElfredaCyania]

Thanks. But what is the ratio of the mass of that Pu in each launch to the launch nuke that you are proposing?

I'm not proposing an amount, I would like to seek information on this idea, mainly on the technological feasibility and its scientific yield. I didn't see a significant technological challenge involved.

 

[berkeman]

I didn't see a significant technological challenge involved.

What other challenges may be involved. Please do not ask us to waste our time on a fruitless hypothetical exercise. That is not what PF is for.

 

[mfb]

Nuclear weapons are only very mildly radioactive before detonation. Various spacecraft launched with 4.4 kW of thermal power from radioactive decays of Pu-238 while a typical uranium-based nuclear weapon might have a few milliwatts, or a million times lower radioactivity. The same system that protects the bomb in the Martian atmosphere could also do that on Earth in the very unlikely case of a launch failure (Falcon 9 has over 300 successful flights in a row), so it's possible you can even recollect the uranium again. There are no significant safety concerns in that aspect.

From a technical perspective and in terms of safety on Earth, such a mission would be no problem.

An explosion on Mars's surface would somewhat mimic an explosion in the upper atmosphere of Earth so satellites orbiting Mars might be affected.

 

[PeroK]

Load nuclear bomb on rocket.
Launch rocket.
Land on Mars.
Detonate nuclear bomb.

What could possibly go wrong?

 

[Klystron]

If the mission is seimographical mapping of the Martian subsurface, nuclear explosions are contraindicated. Your objective is to generate acoustic waves tuned to the Martian 'regolith', not destroy a city.

Nuclear weapons concentrate maximum destruction in a relatively small volume. Seismic charges are much smaller yeild chemical explosives tuned for your detectors and soil of interest. The objective is good data, not maximum destruction. For mapping Mars, explosives of any sort may not be required. A neutral payload can be dropped from orbit using kinetic energy to create seismic disturbances.

 

[Vanadium 50]

I think the OP needs to put a lot more work in. As it stands, it reads like "Here's an opportunity for you guys to do my calculations for me". In particular it needs to be much clearer as to what would be learned. "Ya know, seismic stuff" won't cut it.

I also think the "no social or political constraints" is naive to the point of being silly.

RTGs are not bombs. Despite what Michio Kaku might imply.

 

[Flyboy]

Agreed with the idea of a kinetic impactor. Land your seismometer network on one launch window, get a nice baseline over the next 26ish months, and at the next launch window, instead of putting the departure stage of another mission on a trajectory that would slingshot it into deep space, aim it for a direct impact, as steep as possible, onto the surface of Mars. Maybe, MAYBE add some sort of heat shielding to keep it intact longer and prevent burnup, but not to the extent that it impacts the main mission. Should provide a nice, sharp impulse.

It worked on the Moon for Apollo, it should still work on Mars.

 

[ElfredaCyania]

Nuclear weapons concentrate maximum destruction in a relatively small volume. Seismic charges are much smaller yeild chemical explosives tuned for your detectors and soil of interest. The objective is good data, not maximum destruction. For mapping Mars, explosives of any sort may not be required. A neutral payload can be dropped from orbit using kinetic energy to create seismic disturbances.

Thanks. I understand that seismic data can be obtained by using chemical or mechanical seismic sources. And rovers like InSight have been collecting data from small impactors, but to obtain deep structure data (eg, mantel and core) which has "remained largely unknown", a more energetic event is required. Such an event (like the 2021-12-24 impact mentioned in the link above) is rare on Mars, and they are also unpredictable for now.

This paper suggested that smaller events are harder to detect than expected, only impactors with >10m craters formed within 400km of InSight offer the most promising chance of detection (this corresponds to an event with seismic energy=25,000J). That paper also showed that an explosion can convert half of the seismic energy into the seismic moment (0.27, edit: this is a modifier, not the overall efficiency) compared to that of earthquakes (0.54) and their relation is log-linear. But it's still more efficient than impactors (~0.1).
(edit: this also means a nuclear explosive device is more effective than a nuclear-powered rocket impactor, be it an NTR or ionic)

The difficulties in picking up small seismic events also lead to seismic data biased towards major and close events (close to rovers.)

Another problem is the limited payload ability of launch vehicles, the energy of a kinetic impactor needs to be carried by the vehicle, but its energy (55GJ for Saturn 4B, which is already a big impactor) is still below that of natural major impactors. The energy of S-4B is roughly 10 tons of TNT (considering the efficiency we might be looking at 4 tons), however carrying such an amount of explosives to Mars seems to be putting the cart before the horse, let alone the weight for safety, setup and controlled detonation. Here is where nuclear detonation comes in.

For now, I think the major challenge would be the installation of the device for underground explosions. The Mars penetrator might be a useful reference. Although its original configuration only allows 15m max penetration, far from what you would expect for a nuclear detonation.

 

[ElfredaCyania]

what would be learned

Sorry for the late response. Actually, it's not only seismic stuff, if the explosion includes surface excavation it will also expose subsurface structures, and the dust ejected will be available for collection and spectroscopies so we can look into aspects like the repository of subsurface ice. But let's stick to seismic stuff since it's way more environmentally friendly.

As I said in my last reply the main scientific interest would be in the mantle and the core of Mars, we weren't able to make direct observations on Mars's core until 2021 thanks to major natural impactors (4MJ and 16MJ), and the largest confirmed impactor (63GJ) later that year provider even more data.
We can obtain detailed deep data on Earth and the Moon only because of Earth's active tectonic activity and the moon's small size (also nuking the moon is dangerous for us). Mars is much larger than the moon and has no active, at least no frequent seismic activities. Waiting for natural impactors is unreliable, existing observations of new Martian impacts suggest that asteroids of a given size impacting the planet are about 3 times more common than on Earth, however, it is still very rare.

See the figure from Asteroids IV, note that asteroids of the same size have different energy when impacting Earth and Mars, the most common asteroid type is near-Mars objects and near-Earth objects, tend to impact planets at their escape velocity. This gives the same Mars asteroid 5 times the energy when it hits the Earth. Thus, in events similar to the 63GJ (these figures are known as seismic energy, not directly applicable in the figure above, the asteroid itself has a size of 12–37 m, let's say 20), we can estimate the weight of the asteroid to be 14K-ish tons based on density data of the Mars impactor (14K ton at 5km/s is 63GJ, I'm assuming 100% kinetic to seismic efficiency just to show how rare big impactors are). This would be a 0.18MT event on Earth, occurring around once half a century on Earth, and once a decade on Mars. Once a decade for an unpredictable Mag 4 marsquake is already not very satisfying, and the way we calculate only means the real probability is much lower.

Considering the limited lifespan of rovers like InSight, which is focused on seismic data for just 4 years, it's impractical to depend solely on natural impacts. Man-made kinetic impactors have previously been noted as insufficiently powerful, hence the consideration of nuclear detonation as a predictable and powerful alternative.

Back to the science yield question. Marsquake is by far our only way to study Mars' deep structure. A larger impact could help with the study of the molten layer within Mars' core, whose discovery is only made possible by the 63GJ event. This grants insights into the core's dimensions and composition, how Mars formed, evolved and became the barren planet it is today.

One of the challenges with relying on natural impactors is the uncertainty (you can see impacts on the impact list with uncertainties going way up to decades) and delay in their detection and characterization. Many impactors are only confirmed after visual identification, which often occurs too late for optimal scientific study, especially for thermal science. By the time an impactor is located and sensors are deployed, the immediate thermal effects have dissipated, making it difficult to study the heat flow resulting from the impact.

In contrast, a controlled nuclear detonation offers a predictable and immediate source of seismic activity. Such an event is also a strong magnetic event, which will aid in magnetic study, particularly on how its metal core reacts to the magnetic event. Plus if we consider the future of Mars exploration and potential colonization, understanding and possibly revitalizing its magnetic field require very detailed information on its deep structural insights, but that might be too Musk.

 

[Baluncore]

Mars is much larger than the moon and has no active, at least no frequent seismic activities. Waiting for natural impactors is unreliable, existing observations of new Martian impacts suggest that asteroids of a given size impacting the planet are about 3 times more common than on Earth, however, it is still very rare.

Why do you need such urgent information about the deep internal Martian structure? Is there a power struggle between two academics with different models, that can only be resolved by a nuclear bomb?

Do you represent a mining company that wants to stake a claim on Mars? How are they going to dig so deep that they could benefit from such deep knowledge?

 

[gmax137]

I understand you don't want to talk about this, but... Mars is not Nevada, you can't nuke it just because you want to. It is not yours.

 

[ElfredaCyania]

I understand you don't want to talk about this, but... Mars is not Nevada, you can't nuke it just because you want to. It is not yours.

I know that I can't nuke it and no one can nuke it at least not soon. I'm not calling for nuking it. Rather, my interest lies in understanding whether the hesitation around this idea stems from its scientific merit and feasibility or primarily from regulatory and ethical concerns (or both).

 

[Frabjous]

Here are a couple of articles from a couple of years ago about analyzing old data
https://eos.org/articles/earths-wobbly-inner-core-illuminated-by-nuclear-explosions
https://www.science.org/doi/10.1126/sciadv.abm9916

 

[ElfredaCyania]

Why do you need such urgent information about the deep internal Martian structure?

Do you represent a mining company that wants to stake a claim on Mars?

There's no power struggle and mining on Mars is not technically feasible with current technology. And if you want a utilitarian answer then I apologize for not having one.

But if we focus on science, Mars' inactive structure preserves a record of its early formation, which is no longer observable on our Earth due to geological activity, for the same reason we have OSIRIS-Ex, study comets and asteroids on Earth and many more space-related stuff. None of these missions are low-cost. And the 2021 Mars impactor just reshaped our understanding of Mars’s core. With rovers and orbiters, we acquired data about the surface and immediate subsurface, but as I quoted before the information below is largely unknown. Information beneficial to future outposts such as geothermal hotspots and resource distribution also relies on this.

 

[Frabjous]

For now, I think the major challenge would be the installation of the device for underground explosions. The Mars penetrator might be a useful reference. Although its original configuration only allows 15m max penetration, far from what you would expect for a nuclear detonation.

They need to be buried, but not necessarily contained. See Fig 4.1 of
https://nap.nationalacademies.org/read/11282/chapter/6

 

[Vanadium 50]

also nuking the moon is dangerous for us

And nuking Mars isn't? How so?

 

[berkeman]

Mars is not Nevada, you can't nuke it just because you want to. It is not yours.

I'm not sure which I'm more worried about...

Mars:

https://www.physicsforums.com/members/peterdonis.197831/

Or Nevada:

https://www.flavourmag.co.uk/special-feature-the-cars-of-mad-max-fury-road/

 

[ElfredaCyania]

They need to be buried, but not necessarily contained. See Fig 4.1 of
https://nap.nationalacademies.org/read/11282/chapter/6

This paper is very helpful, it would suggest a rover capable of digging a few meters such as ESA's ExoMars can install a very large fully-coupled bomb. It mentioned that rock type may affect its effect but doesn't seem to provide more detail, including in Appendix C. Martian soil (cohesionless soil) has a lower density (~1.37) than hard rock on Earth and you'll need to penetrate 3 to 5 m to reach quartz sand, this depth was design for the InSight who failed to penetrate that deep due to lack of friction for its drill. Harder Martian crustal rock would be too deep (in km) to reach it. Of course, a ground penetrator is free from friction problems but we are probably limited to installing an unconfined nuke in Martian soil.

What's left is that an unconfined nuke will produce a lot of ejecta. Ejecta is good for science but I didn't find more information on its contamination. What's known is that buried but not contained nuclear explosions produce much more radioactive fallout but concentrate in a narrow column instead of rising into the high atmosphere (Mars doesn't have much atmosphere anyway, but the lower gravity would certainly make ejecta go higher).

Also here's a picture showing the depth required to contain a nuke.

 

[Frabjous]

I would not focus on the ejecta. Surface properties are measurable other ways.

 

[Astronuc]

This paper is very helpful, it would suggest a rover capable of digging a few meters such as ESA's ExoMars can install a very large fully-coupled bomb. It mentioned that rock type may affect its effect but doesn't seem to provide more detail, including in Appendix C. Martian soil (cohesionless soil) has a lower density (~1.37) than hard rock on Earth and you'll need to penetrate 3 to 5 m to reach quartz sand, this depth was design for the InSight who failed to penetrate that deep due to lack of friction for its drill. Harder Martian crustal rock would be too deep (in km) to reach it. Of course, a ground penetrator is free from friction problems but we are probably limited to installing an unconfined nuke in Martian soil.

What's left is that an unconfined nuke will produce a lot of ejecta. Ejecta is good for science but I didn't find more information on its contamination. What's known is that buried but not contained nuclear explosions produce much more radioactive fallout but concentrate in a narrow column instead of rising into the high atmosphere (Mars doesn't have much atmosphere anyway, but the lower gravity would certainly make ejecta go higher).

Er, what could go wrong?

https://en.wikipedia.org/wiki/Operation_Plumbbob#Missing_Neenah_Foundry_lid

During the Pascal-B nuclear test of August 1957,[8][9] a 900-kilogram (2,000 lb) iron lid was welded over the borehole to contain the nuclear blast, despite Brownlee predicting that it would not work.[8] When Pascal-B was detonated, the blast went straight up the test shaft, launching the cap into the atmosphere at a speed of more than 66 km/s (41 mi/s; 240,000 km/h; 150,000 mph). The plate was never found.

https://nuclearweaponarchive.org/Usa/Tests/Brownlee.html

Also here's a picture showing the depth required to contain a nuke.

The figure is for earth (and earth's gravity). Mars has a lower surface gravity, so one would have to bore deeper - more than double, and perhaps triple.

The average gravitational acceleration on Mars is 3.72076 m/s² (about 38% of the gravity of Earth) and it varies.

https://en.wikipedia.org/wiki/Gravity_of_Mars

Note in the figure, the scale only goes to 100 kt.

The comment

This paper is very helpful, it would suggest a rover capable of digging a few meters such as ESA's ExoMars can install a very large fully-coupled bomb.

is rather vague and incongruent. What yield is a 'very large fully-couple bomb'.


Before employing a nuclear device, one should determine the energy and explore a non-nuclear method for achieving such energy, e.g., from an impact of say 1 or 10 tonne accelerated into the Martian surface.

 

[ElfredaCyania]

Mars has a lower surface gravity, so one would have to bore deeper - more than double, and perhaps triple.

I've just found a paper for this, the crater diameter for the same explosive charge D is proportional to g^-1/6, which means a Martian crater is likely to be 1.176 times as big as an Earth one. According to the paper, its conclusion holds for buried and zero-depth charges, as well as the cohesionless soil of Mars. The soil used in the paper has a similar density to Martian soil. On page 3839 in 4.3 it mentioned the condition for a charge to crater. The optimal depth to crater is the critical depth d_c, calculated using d_c=C₀/ρg, where C₀is the cohesion (100-1000 Pa for Martian regolith, Chang et al.), ρ is density (1.37 as mentioned earlier), and g is Martian g, 3.71. The critical depth would vary between 20 m and 200 m. It is achievable with the current ground penetrators on the soft Martian sand but this doesn't say anything about the choice of yield.

Crater efficiency is discussed on page 3835 but I haven't found numbers for nuclear bombs yet. But if we assume a nuclear bomb is somewhere between the explosives shown in Fig.1 and the sand is Ottawa sand (the most similar to the regolith) we may say the crater efficiency for 1e7 to 1e9 J bomb is around 10^1.5 or 30. And it can go as low as 15 at 1e11 J. This is a bad sign for nuclear detonation but only in terms of efficiency.

Before employing a nuclear device, one should determine the energy and explore a non-nuclear method for achieving such energy, e.g., from an impact of say 1 or 10 tonne accelerated into the Martian surface.

I agree that we lack the data for designing a nuclear detonation, for now. We need data for the underground structure of Mars (considering the depth we are targeting, a Borebot-like mission is required), the effect of explosives on Martian regolith (installing a bomb would be better but artificial impactors or observing existing crater will also do the job).

Er, what could go wrong?

As for this, it highly depends on the mission design, like installed by the rover, penetrator bomb or delayed penetrator bomb. But for penetrators, after penetrating to a depth of around or more than 15 m, the soil would move back and rebound, burying the warhead (See page B-2 of the Mars Penetrator concept).

For risk control, it would be similar to any controlled nuclear detonation or ground penetrator and it needs to be solved by engineering.

What yield is a 'very large fully-couple bomb'.

I said that because even a small bomb like the current active B61-12 in the US assets is 100 times more energetic than the 2021 63GJ event at its 1.5 kt configuration (50 times, considering the inferior efficiency of explosion compared to an earthquake, explained before). And for such a 1.5 kT bomb to be fully coupled, you only need a depth of 3.45m on Earth. (Maybe ~2.6 times on Mars, but I currently didn't find direct data to support this, the critical depth is 2.6 times for sure)

I would like to add that a nuclear detonation is a "very sharp, very brief, very powerful" seismic source according to Vidale from this report. Also, I would like to quote from the preface of Explosion Source Phenomenology: "Data from nuclear tests provide the most directly useful observations and constitute the most effective benchmarks for a quantitative evaluation of our forward-modelling capabilities.", particularly on a planet like Mars where significant geological activity is minimal. We are not able to rule out nuclear methods in deep seismology in the foreseeable future.

 

[Astronuc]

I would like to add that a nuclear detonation is a "very sharp, very brief, very powerful" seismic source according to Vidale from this report. Also, I would like to quote from the preface of Explosion Source Phenomenology: "Data from nuclear tests provide the most directly useful observations and constitute the most effective benchmarks for a quantitative evaluation of our forward-modelling capabilities.", particularly on a planet like Mars where significant geological activity is minimal. We are not able to rule out nuclear methods in deep seismology in the foreseeable future.

An explosive like C-4 (or RDX+TNT, or HMX+TNT) is also fairly sharp.

A tungsten penetrator from orbit might work. Where possible, it's best to use an inert (non-radioactive) material/system.

One would want a network of seismic detectors placed around the Martian surface, from which one could apply both reflection and transmission seismology.

Nuclear explosives produce a neutron flux, which activates (by neutron absorption) all matter surrounding the device, in addition to fission products and transuranic elements, all of which are vaporized, and they either permeate the surrounding matter or a dispersed in the environment (aka fallout).

 

[ElfredaCyania]

they either permeate the surrounding matter or a dispersed in the environment (aka fallout)

Contamination is the most tricky part of this whole idea and it's hard to find concrete data for this. From what I have known, we can take the SEDAN test, it's one of the two most radioactive nuclear tests in the US, and it's shallowly buried--analogous to the one on Mars. Unlike power plants, the fallout of nuclear explosions has a much shorter half-life, but 249Pu is still a major concern (only considering pure fission here). Anyway, the radiation in the Sedan crater dropped from 500 Rr/h to 500mR/hr in 27 days, and to 35mR in half a year. Its 1990 reading at the most radioactive place is 0.053 mrem/hr or 0.00053 mSv/hr, which is considered safe for tourist visits.

https://en.m.wikipedia.org/wiki/File:Nevada_Test_Site_-_Sedan_Crater_-_1.JPG

Meanwhile, Mars has an all-time radiation dose of 240-300 mSv/yr (0.027-0.034 mSv/hr) due to its thin atmosphere. The Sedan crater was the result of a 100kt bomb plus the background radiation from all the other tests in Nevada. This suggests that, purely from a health risk perspective and over time, such a site would be no more hazardous than the general Martian environment by the time humans can stand in that crater.

But the complexity comes from the Earth's weather, rain, while rare in Nevada is an example of a radiation wash-out mechanism on Earth, wind can also move the radiation around. Mars has no rain and its wind is fast but weak. Also, Martian regolith may affect the induced radioactivity since it is mainly basalt. Besides, Martian fallout tends to be concentrated due to a lack of weather (similar to the Moon in project A119). Other influencers like the effect of gravity are not well-documented as far as I searched.

Ethically speaking it's always bad to bring radiation there but considering the cost-effectiveness of creating the largest events, there might be a trade-off.

 

[ElfredaCyania]

Many are worried about a launch failure so I did some math on this, all assuming the plausible worst-case scenario.

In a famous broken arrow (in which you lost a nuclear warhead) 1966 Palomares B-52 crash, and two B28 1.45MT H-bombs (this is bigger than any nuke you would want on Mars) were released and crashed into the ground, releasing some Pu-239. ofc the design of B28 is classified but we assume it's the worst thermonuclear weapon possible, only 20% of its yield is from fusion, 80% from fission, and its fission efficiency is also 20%, pretty much a Fatter Man. Then we are looking at 711 kg of 239Pu in total (this is 71 times its critical mass, enough to make a 14.4MT bomb on its own, there's no way the B28 is that bad). With its specific activity of 2.3 GBq/g, we have 1.64e15 becquerels. Then we assume the fail-safe failed (see safety data for the New Horizon, if we use its setup, the chance is 4/62 in catastrophic fail). That's not enough, we want maximum contamination, so it can't break up in the air, can't go into the ocean (no one could bother if it ends up in the ocean with all the fissionable we've dumped in the ocean). So it landed on the land (which is impossible unless your rocket experiences severe control problems & self-destruction failure and delivers the thing to the land while in one piece). The Pu-239 magically dispersed into the land evenly and instantly, akin to the distribution of the Hanford Site, one of the most costly sites to clean up. It would cost 17,500 per Curie, so our becquerels would cost 775.7 million dollars.

Even deliberating such a contamination would be challenging, that's pretty much a coordinated dirty bomb attack.

Now let's see what if a regular mission goes wrong a bit, you will lose,150 million for Hayabusa2, 250 million for each GPS 3F, 316 million for NROL-87, 1.7 billion for the Challenger, 2.2 billion for the Perseverance, and 9 billion if you crash the JWST. Yet these missions used launch systems with a safety record inferior to Falcon 9's current track record.

You get the idea.

 

[Astronuc]

I was listening to a program on the 'Polygon' tests in Kazakhstan (1949-1989), where the USSR did atmospheric testing and underground testing. Some tests produced significant craters, and even some underground tests produced fractured formations such that radionuclides found their way out of the underground caverns in the Degelen Mountains. The USSR did test some large yield devices. The area remains heavily contaminated with fission products, U, Pu and TU residues.

https://en.wikipedia.org/wiki/Semipalatinsk_Test_Site

Later tests were moved to the Balapan complex by the Chagan River in the southeast of the Semipalatinsk Polygon, including the site of the Chagan test, which formed Chagan Lake. Once atmospheric tests were banned, testing was transferred to underground locations at Saryozen, Murzhik in the west, and at the Degelen mountain complex in the south, which is riddled with boreholes and drifts for both subcritical and supercritical tests. After the closure of the Semipalatinsk labour camp, construction duties were performed by the 217th Separate Engineering and Mining Battalion, who later built the Baikonur Cosmodrome.

Between 1949 and the cessation of atomic testing in 1989, 456 explosions were conducted at the STS, including 340 underground borehole and tunnel shots and 116 atmospheric, either air-drop or tower shots. The lab complex, still the administrative and scientific centre of the STS, was renamed Kurchatov City after Igor Kurchatov, leader of the initial Soviet nuclear programme. The location of Kurchatov city has been typically shown on various maps as "Konechnaya", the name of the train station, now Degelen, or "Moldary", the name of the village that was later incorporated into the city.

Sometimes a crater forms when the ground collapses into the cavity that is produced. The ground above sometimes ruptures, even if it is not pulverized.
https://en.wikipedia.org/wiki/Semip...-_Flickr_-_The_Official_CTBTO_Photostream.jpg

One would probably need a deep bore hole (km or more), which would require a drilling rig, not something one puts on a small 'rover'.