Should we hit Mars with The Behemoth Comet?

[tsmspace]

I want to know why no one thinks we should hit Mars with The behemoth comet, C/2014 UN271 (Bernardinelli-Bernstein)

after watching this fun video

It is for the very highly educated, I know, that's what I am.

Basically,, how much of a propellant push could nuking the behemoth comet result in? Would we be able to change the course of the behemoth comet enough to hit mars, using a series of nukes? (these nukes would result in outgassing, basically, propelling the comet). I don't know what sort of consideration there would need to be for the rotation of the comet, but it seems that the nuke would glow for a bit, and outgassing would basically only occur during this period of heating, and for a short while afterwards, so perhaps the only consideration is the position of the burst relative to the comet, and the rotation of the comet may be just that as long as it's a bit slow, then the gas will basically outgas towards the nuke.

Then, we could hit Mars one good time, and if it gets too hot, we can probably find a way to cool it. (I mean, by using geo-thermal power plants that are able to float on burning hot magma)

 

[phyzguy]

You underestimate the energy involved in astronomical objects, or perhaps you overestimate the energy output of a nuclear weapon. I did some rough calculations, and to accelerate the comet up to Mars orbital speed, assuming 100% of the energy of a nuke is converted to kinetic energy of the comet (a very unlikely assumption), would require more than 2 million 10 Megaton nukes. The US arsenal is currently about 5000 nukes, most of which are probably smaller than 10 Megatons. We won't even talk about how you would get 2 million nukes out to Saturn's orbit. In other words, there's no way to do what you are envisioning.

 

[tsmspace]

I wrote this on my phone at work on break, so I will quote it, then comment some more.

Well,, you wouldn't be using the energy of the nuke to propel the comet, you would be using the resulting outgassing to do so. And the amount of energy produced by outgassing will not be equal to the energy of the nuke, because it will not be a 1 to 1 joules of radiation to gas evaporated, and then the amount of energy in the gas evaporating and pushing away will not be 1 to 1 joules of evaporation to thrust. I don't mean to suggest it will be like a spark plug to a compressed chambered fuel mixture, but the energy of the nuke radiation will heat the surface, which will cause a chemical state change in some amount of matter, some of which will convert to gas and come under pressure, etc.

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So, I am basically picturing that using the energy of a nuke-blast to figure the resulting thrust is probably just the first part of the equation, and there are a lot more things to consider. The composition of the comet might result in a variety of behavior from the resulting radiation, anywhere from sublimation of some ice to actual combustion of gases, or perhaps even some latent radioactive material. Basically, the actual energy released in the explosion isn't what pushes the comet.

granted I could be amiss on this one, as you know I am just a filthy casual gamer. Still, I feel certain that there is more to the story, and besides mars, there is certainly some perceivable benefit to trapping the super ultimate comet into closer proximity. For example,, the comet is set to launch back out into a massive (what did the article say, billion year trip back out from the solar system??) , which means it's gone for good as far as we're concerned, good for a nice picture and that's about it. But,, what if we slowed it down enough to change it's orbit enough that it can be expected back,,, perhaps a bit sooner?? We don't need to smash it into Mars the first go-round,, we can just satisfy ourselves with a bit of jurassic park style experimentation, and redirect it enough that we can expect to be ready to catch it next time??

 

[phinds]

I want to know why no one thinks we should hit Mars with The behemoth comet, C/2014 UN271 (Bernardinelli-Bernstein)

Can you offer any support of that statement?

 

[tsmspace]

Can you offer any support of that statement?

that's true I actually have no idea if anyone thinks it or not.

 

[Melbourne Guy]

Well,, you wouldn't be using the energy of the nuke to propel the comet, you would be using the resulting outgassing to do so.

Assuming outgassing after a nuclear strike is sufficient to significantly divert the comet's orbit, how do you steer it? The outgassing event duration and direction would be somewhat unpredictable, so you're more likely to send it careering around the Solar System than smash it into Mars.

 

[phinds]

that's true I actually have no idea if anyone thinks it or not.

Good answer. Keep in mind that this is a science forum. Unsupportable claims made as statements of fact will not go over well, which is the point I was making w/ you.

 

[Nik_2213]

IMHO, blowing off a significant area and depth of the 'coke-like' de-volatilised surface to expose 'juicy' interior would likely provide a fair jet effect. Unfortunately, given comets seem to have a very non-uniform make-up, the effects would be too unpredictable. Worse, you'd have to do it on rotation axis, and hope no 'wobble' develops...

IIRC, not only did the 'Deep Impact' hyper-velocity impactor leave a much smaller, shallower crater than hoped on its target, but neither impact nor, more importantly, subsequent out-gassing from fresh crater had any significant effect on comet's motion...

Um, surely, you would not have to match speeds with Mars, it just has to go inside 'capture' zone ??

I'm sort of sorry that comet missed Mars about a year back. Okay, such impact probably kills the landers and rovers, but would have provided a lot of data for 'terraforming' modelling...

And, yes, given would have been so much closer, rival the Shoemaker-Levy Jovian event for sheer spectacle...

 

[tsmspace]

Assuming outgassing after a nuclear strike is sufficient to significantly divert the comet's orbit, how do you steer it? The outgassing event duration and direction would be somewhat unpredictable, so you're more likely to send it careering around the Solar System than smash it into Mars.

I'm sure that would be the hardest part, but I guess at that point they would be committed to trying their best. Besides, if it's a miss, the comet shouldn't be back for a few billion years, I mean the chances of accidentally hitting Earth are basically 0 if the energy isn't in there anyway.

 

[Astronuc]

I want to know why no one thinks we should hit Mars with The behemoth comet, C/2014 UN271 (Bernardinelli-Bernstein)

Orbital period	≈ 2.75 million yr (inbound) ≈ 4.47 million yr (outbound)

C/2014 UN₂₇₁ (Bernardinelli–Bernstein) is approaching the Sun and will reach its perihelion of 10.9 AU (just outside of Saturn's orbit) in January 2031. It will not be visible to the naked eye, it will not enter the inner Solar System.

https://en.wikipedia.org/wiki/C/2014_UN271_(Bernardinelli–Bernstein)

It takes a while to manufacture a spacecraft , then launch it toward Saturn. NASA's Cassini mission launched on October 15, 1997. Closest approach to Jupiter occurred December 30, 2000, and the spacecraft had orbital insertion around Saturn on July 1, 2004.
https://en.wikipedia.org/wiki/Cassini–Huygens

If we had such a rocket/ spacecraft , and a mission, we might get a spacecraft to Bernardinelli–Bernstein in 8 years in time to watch it leave. We are not going to deflect it toward Mars.

 

[Vanadium 50]

It is for the very highly educated, I know, that's what I am.

I don't think it is, and frankly, I don't think you are. You can crow about how smart you are, but I think it's better to show it.

One way is to do your homework. If this is to provide a Martian atmosphere, How much does the Earth's atmosphere weigh? How much does this comet weigh? Google will tell you both answers in under a second. You're short an order of magnitude.

If this is to heat up Mars, how much energy is contained in a comet of this mass impacting at Martian escape velocity? How long does it take Mars to receive this energy from the sun. This took a minute, 50 seconds of which were spent looking for my calculator. A couple years.

If this is to make Mars habitable, how many people have flown to Mars? Zero. half-way? Zero. 10% of the way? Still zero. 1% of the way? Still zero. 0.5% of the way? Now we're getting somewhere. 24. What's the rush?

There is no magic with outgassing. You need energy to change the orbit and that energy has to come from somewhere. In fact, you need to lose energy to come in closer, and that means transferring energy from one part of the comet to another. @phyzguy has an estimate - you need a huge amount of energy to do anything substantial. One nuclear war and dozens of nuclear tests diodn't change the Earth's orbit, did it?

You may be "very highly educated", but I don't think you've done your homework, and education - homework in the past - is not a substitute for homework in the present.

 

[tsmspace]

I don't think it is, and frankly, I don't think you are. You can crow about how smart you are, but I think it's better to show it.

One way is to do your homework. If this is to provide a Martian atmosphere, How much does the Earth's atmosphere weigh? How much does this comet weigh? Google will tell you both answers in under a second. You're short an order of magnitude.

If this is to heat up Mars, how much energy is contained in a comet of this mass impacting at Martian escape velocity? How long does it take Mars to receive this energy from the sun. This took a minute, 50 seconds of which were spent looking for my calculator. A couple years.

If this is to make Mars habitable, how many people have flown to Mars? Zero. half-way? Zero. 10% of the way? Still zero. 1% of the way? Still zero. 0.5% of the way? Now we're getting somewhere. 24. What's the rush?

There is no magic with outgassing. You need energy to change the orbit and that energy has to come from somewhere. In fact, you need to lose energy to come in closer, and that means transferring energy from one part of the comet to another. @phyzguy has an estimate - you need a huge amount of energy to do anything substantial. One nuclear war and dozens of nuclear tests diodn't change the Earth's orbit, did it?

You may be "very highly educated", but I don't think you've done your homework, and education - homework in the past - is not a substitute for homework in the present.

that was a joke. I have no education particularly no relevant education. I understand how easy it is to miss context that isn't presented, so I expected someone to not know I was joking with that line. Please understand it is unlikely for me to be doing any such homework, therefore, because I wouldn't know where to begin.

I appreciate your reply, though, so thank you.

well,,, I know that comets have a lot of water ice,, but they might have hydrocarbon ices as well? Would the comet be combustible? Perhaps hitting it right would ignite some amount of it, changing just how "impactful" a nuke would be? I realize it's a pretty big comet, but on the other hand, comets DO change velocity from their outgassing, and as for Earth's orbit changing from nukes, well,, Earth is really really big compared,

So how about this,,, a nuke or several manage to hit the comet head-on, resulting in some ignition of comet ices as they evaporate, and although the nuke has a negligible effect on the comets trajectory, it DOES do two things,, it causes the comet to outgas very powerfully for a short while,, but then ALSO weakens the surface of the comet so that when the comet gets closer to the sun, the radiation from the sun is able to result in much more significant outgassing than it would on a totally frozen oort cloud object, further slowing the comet, so that it enters into a significantly shorter orbital period as a result. (and actually isn't the BEST time to decelerate for de-orbiting an object just after the perihelion? So the most efficient nukes (or other radiation method) would be from 2031 on out,, so perhaps some sort of reactor could be launched to lead the comet out, so that it could then continue to slow the comet for a significant time period, perhaps if nothing else bringing it close enough that generations in the future would see it as useful?

 

[Melbourne Guy]

Would the comet be combustible?

You'd need more than just hydrocarbons for combustion, I'm thinking

 

[jbriggs444]

radiation from the sun is able to result in much more significant outgassing than it would on a totally frozen oort cloud object, further slowing the comet, so that it enters into a significantly shorter orbital period as a result.

You are up against a scaling factor. The surface area to volume ratio.

In order to get good outgassing, you need a lot of surface area to absorb a lot of solar radiation. But when you look at larger and larger comets, their volume increases more rapidly then their surface area.

Volume (and, therefore, mass) rises as the cube of a comet's radius.
Surface area rises as the square of a comet's radius.

Ordinary comets can survive multiple passes near the sun without having their orbits massively affected. Larger comets passing nowhere near the sun will not be significantly affected.

Also, the net thrust from outgassing will tend to be in a radial direction directly away from the sun. This will not tend to decrease the distance achieved at perihelion, but rather to increase it.

 

[tsmspace]

You'd need more than just hydrocarbons for combustion, I'm thinking

it should mostly be water ice right?

 

[jbriggs444]

it should mostly be water ice right?

The problem is that hydrocarbons do not burn without an oxidizer. Water ice is not an oxidizer. It is already burned.

 

[Vanadium 50]

The problem is that hydrocarbons do not burn without an oxidizer.

Well,that is a problem,. The problem is that the OP keeps whacking us with new "what-ifs" without doing any homework on the old ones.

It would help a lot if the OP were clearer in a) what he intends to achieve, and b) what the constraints are. Two million nuclear bombs and the lack of suitable launch vehicles didn't even slow him down. Is there even a launch window to get there by perihelion? And it has an inclination of 95 degrees - how does one deal with matching that velocuty?

Before we ask "should we" we need to ask "can we" (unless, as I suspect, we're just playing 'lets pretend') and the answer to that is "no".

 

[TeethWhitener]

Here’s a Venus terraforming proposal where they examine bumping a Saturnian moon into the inner solar system:
https://www.orionsarm.com/fm_store/TerraformingVenusQuickly.pdf
Their suggestion is basically a solar focusing mirror to create a steam jet for propulsion. The advantage of using a moon is that you don’t have to chase it as it leaves the solar system. The downside is that moons are huge (and might have life, in the case of Enceladus). Centaurs might be another option, as most of those are water-rich, and not gravitationally bound to a gas giant.

 

[tsmspace]

The problem is that hydrocarbons do not burn without an oxidizer. Water ice is not an oxidizer. It is already burned.

Ok, so if you supposedly nuke the water ice, none of it becomes available to be an oxidizer?

 

[Algr]

Ok, so if you supposedly nuke the water ice, none of it becomes available to be an oxidizer?

The end product of oxidizing hydrocarbons is CO₂ and Water. If you are starting with water, then you will never get back any more energy than you started with, and will probably just waste most of it on spreading diffuse heat and dust everywhere.

The problem with outgassing is that almost all stellar objects rotate. So even if outgassing produced thrust, you would have no control over what direction that thrust was pushing the object.

I'm as much for smacking up Mars as anyone, but it is a very difficult thing to do. I'm sorry, but unless you can do some of the math, physics, or chemistry involved, people on this forum are just going to get frustrated with your ideas.

 

[phinds]

... unless you can do some of the math, physics, or chemistry involved, people on this forum are just going to get frustrated with your ideas.

I don't mean to be harsh, but to quote PAllen: (https://www.physicsforums.com/threads/can-absolute-velocity-be-measured.593517/#post-3851683)

Note, we are not called the "idle speculation without understanding or knowledge forums".

 

[tsmspace]

The end product of oxidizing hydrocarbons is CO₂ and Water. If you are starting with water, then you will never get back any more energy than you started with, and will probably just waste most of it on spreading diffuse heat and dust everywhere.

The problem with outgassing is that almost all stellar objects rotate. So even if outgassing produced thrust, you would have no control over what direction that thrust was pushing the object.

I'm as much for smacking up Mars as anyone, but it is a very difficult thing to do. I'm sorry, but unless you can do some of the math, physics, or chemistry involved, people on this forum are just going to get frustrated with your ideas.

Ok, but if you start with water, then the nuke results in a bunch of gas creation, this expansion would be thrust, and then if you engage some also evaporated hydrocarbons and the same time to combust with the now available oxygen, this would result in more thrust. So, your energy balance wouldn't zero unless all of the matter then fell back to the comet, so as long as you just leave it behind, you don't have the problem of getting more energy out of the water, you actually get to first free the oxygen with the nuke, netting expansion energy, and then you get to engage the hydrocarbons in combustion, netting more expansion energy.

as for the rotation yes that's something even the layperson looks at immediately, (me) but if it really is quite a large object, then it probably isn't rotating THAT quickly, and perhaps it's imaginable to time it to still result in a net push in a desired direction as long as the reaction takes place mostly within half a rotation. It's also possible that you could target one of the poles, but I don't know that I think it would be tumbling, I suppose I picture it would just be rotating in line with it's orbit.

 

[Algr]

:: Goes to sleep. ::

 

[jbriggs444]

Ok, but if you start with water, then the nuke results in a bunch of gas creation, this expansion would be thrust, and then if you engage some also evaporated hydrocarbons and the same time to combust with the now available oxygen, this would result in more thrust.

The rule in energy conservation is that you do not get something for nothing.

If the nuking of water ice results in the creation of free oxygen and free hydrogen, then that reduces the kinetic and thermal energy of the blast accordingly. If the free oxygen re-combines with the hydrogen then you get that energy back. If the free oxygen combines with some hydrocarbon vapors instead then you still get approximately the same energy back. You do not get more energy out than the nuke put in.

Look at it this way: Is there an exothermic chemical reaction possible between water and hydrocarbons? What is the resulting product? How many kcal's per mole does this reaction produce?

Setting that all to one side, a very small fraction of the energy in the nuke burst will manifest as bulk kinetic energy in the comet. Regardless of what you do, the vast majority will be wasted on the thermal, kinetic and X-ray energy in the rapidly expanding debris field. Post #2 made the generous assumption that this was not the case and still concluded that the number of nukes required was fantastically exorbitant. You cannot rescue the scheme by proposing a self-sustaining water-hydrocarbon reaction that results in a unidirectional natural rocket motor propelling the comet on a planned trajectory.

 

[Vanadium 50]

You're all just a bunch of naysayers with your math, and physics and conservation of energy and stuff.

 

[Nik_2213]

Yeah, a former colleague would say that each time I trivially falsified yet-another of his 'perpetual motion, over-unity and/or zero-point energy' notions...

( "Run IC Engine on water !" Sorry, there's a world of difference between water-injection to prevent eg a drag-racer's engine melting due nitro boost, and pouring a gallon of tap-water into his car's empty gas-tank. Even with a couple of fridge-magnets clamped to fuel line. {Sigh...} )

 

[Algr]

if you engage some also evaporated hydrocarbons and the same time to combust with the now available oxygen, this would result in more thrust.

I just answered this. You aren't going to get any thrust by separating atoms and then clumping them back together again. In fact, because of the initial nuclear blast, the re-oxidation would happen far away from the comet and provide no thrust at all. Thus you would get less total thrust then if the blast had never separates any molecules.

but if it really is quite a large object, then it probably isn't rotating THAT quickly,

How quickly does the Earth rotate? How quickly does a typical comet rotate? These are questions you ought to be able to think of and look up yourself. If you can multiply and divide you can work out how many times the the comet would it rotate between the initial blast (beyond Saturn) and when it reaches Mars's orbit.