# Is using the Sun as a sort of 'garbage dump' safe?

Is it safe for my civilization to launch rockets full of hazardous material into the Sun? This question applies to all stars, really, not just the sun.

By hazardous materials, I mainly mean radioactive waste. Just so I don't get answers about how the rockets need special materials and it's not very cost effective, disregard the method of transportation for a moment and focus on the part where the stuff enters the Sun.

Is there any element/polymer/material/anything we have today that could harm the Sun if we dumped it into it? Although I'm doubtful that there would be negative effects, would dumping large amounts reduce the life of the Sun? (I'm mainly concerned if it changes the life by at least a few thousand years.) If you know how long it would reduce the life, go ahead and put it in the answer, as I'm sure someone will find it helpful.

• Comments are not for extended discussion; this conversation has been moved to chat. – L.Dutch - Reinstate Monica Jul 22 '20 at 15:42
• Pretty difficult to get something there, from what I understand (see this link). – MPW Jul 22 '20 at 19:39
• This has been attempted by Scott Manley: Sending trash into the Sun. – Edgar Bonet Jul 22 '20 at 19:45
• This reminds me of a funny story my dad told me once. Him and one of his co-workers were discussing the idea and the co-worker's wife walked up and asked, "But wouldn't that pollute the sun?" My dad had pointed out that you could throw the entire Earth into the sun and it would probably not even react to it. I think that kind of answers the question, but I didn't have enough to contribute beyond that story to provide a proper answer (unless someone wants to tell me otherwise.) – Arvex Jul 23 '20 at 2:57
• @SolomonSlow: It's the same either way. They're both achieved most efficiently by (ultimately) a Jupiter slingshot. – Joshua Jul 23 '20 at 15:48

If you could get the materials safely away from Earth and actually dump them in the Sun, no, there would be no danger.

The Sun is approximately 330,000 times the mass of Earth. To substantially change its evolution, you'd likely to need add - and I'm really just making an educated guess here - something on the order of $$\sim0.01M_{\odot}$$, where $$M_{\odot}$$ is the astronomer's notation for solar masses. Clearly, that's impossible to attain using just the material on Earth. Each year, the Sun loses roughly $$10^{-13}M_{\odot}$$, which comes out to around $$10^{14}$$ tons. However, humans produce about $$10^9$$ tons of trash each year, meaning that we'd have to dump about 100 centuries' worth of trash into the Sun to simply negate the mass it loses each year.

It's also unlikely that any dangerous materials would come back to haunt us. While the Sun does occasionally display bouts of activity, such as coronal mass ejections and solar flares, the material is dissipated throughout space, and the odds of the ejected matter containing our waste in significant quantities are extremely low. Odds are good that it will simply mix throughout the solar photosphere (in its now-ionized form) and never come close to Earth. The solar wind, which is fairly constant, is also not a substantial risk for essentially the same reason.

If the Earth were to be engulfed by the Sun, it likely wouldn't cause much of a change to the Sun's evolutionary track. It would, however, be noticeable, causing changes to the composition of the solar photosphere. We've seen this in, among other cases, the star HD 240430, which seems to have eaten several terrestrial planets, leading to a significant enrichment of photospheric metals. However, as this is only a change on the surface, its unlikely that the matter will affect the behavior of the stellar core and inner layers, and by extension it will not significantly influence its evolution.

If you really want to run the numbers: The main sequence lifetime of a star is approximately $$\tau=10^{10}\left(\frac{M}{M_{\odot}}\right)^{-2.5}\;\text{years}$$ where $$M$$ is the mass of the star and $$M_{\odot}$$ is one stellar mass. It turns out that if you compare the cases where $$M=M_{\odot}$$ and $$M=M_{\odot}+M_{\oplus}$$ (where $$M_{\oplus}$$ is one Earth mass), i.e. the current lifetime and the lifetime if the Sun swallows the Earth, you get a difference of something like 75,000 years. For a star that should live about 10 billion years before leaving the main sequence, that's not much.

Now, as I alluded to at the beginning, we do have to deal a side effect of the problem of getting matter to the Sun. From an orbital mechanics perspective, I'd argue that it's not a major issue; it's not easy to get to the Sun, but it's far from impossible. However, if the rocket explodes - either on the launch pad or in the air - that waste would be spread out across the surface, and the resulting fallout could cost many lives.

Is this idea safe? Once you're out of Earth orbit, yes. Before that . . . maybe not.

• As a tangential followup to your answer, could a civilization living on an earth-like planet push enough waste into a star for the emissions to be detectable as a sign of intelligent life? (I'll leave the question of "if you're making that much waste and can't recycle it, how intelligent can you be?" for another day.) – JBH Jul 21 '20 at 23:17
• @JBH That's a fascinating question. Put enough of anything into a star's photosphere, and it'll show up in a spectrum; I guess you'd see lines from various metals, as well as substantial amounts of carbon and certainly the heavier elements, if it's radioactive waste. That said - I don't know if astronomers know much about the emission lines of, say, uranium, so those lines might be interpreted as something completely different. – HDE 226868 Jul 21 '20 at 23:32
• Good answer, but you may want to explain your stellar mass symbol a bit earlier in the post. – gerrit Jul 22 '20 at 7:24
• I'm kind of curious how much nuclear waste you'd have to dump into the sun in order for it to show up as a recognisable blip on a spectrograph. Presumably it's more of a matter of sensitivity. But the sun has plenty of most elements somewhere, so you'd have to increase one of them significantly enough to be recognisably artificial. – Ruadhan Jul 22 '20 at 8:21
• "Now, we do have to deal with the problem of getting matter to the Sun. From an orbital mechanics perspective, I'd argue that it's not an issue" -- it's surprisingly hard to hit the sun – canton7 Jul 22 '20 at 16:10

# Dumping radioactive waste into space was actually considered in the real world

The idea of launching hazardous waste into the sun is completely absurd on so many levels. Or is it? Let's look at the real world studies that seriously considered it. HDE 226868 has a terrific answer about the physics involved, so I'll stick to the history.

The 1978 NASA report Nuclear Waste Disposal in Space approved of the idea dumping waste into space: "Of the five space destinations considered, the lunar surface and solar orbit options are the most attractive..." The report declines to support solar impact disposal of nuclear waste only because it was beyond the rocket power available at the time.

A 1981 report went so far as to rank the different ways of hurling nuclear waste into space. Sending the waste directly into the sun was ranked last.

The same report illustrated the general procedure for launching radioactive waste into space.

Now to address your question. The idea of shooting waste into the sun has appeared again and again over time, and a study from 2011 answers exactly what you want to know:

The underlying principle here is that all matter caught in the sun’s gravity will lose its structural integrity due to the stress of gravitational forces and “break up” before reaching the sun. Moreover, high temperatures will incinerate and completely consume all matter prior to its reaching the sun’s corona. Specifically, as matter heats up, it expands beyond its structural integrity, and the heat energy encountered causes molecular bonds to break. Even the atomic integrity of elements of atomic number above two (i.e., helium) does not exist within the sun. Essentially, the intense heat renders such elements into their composite subatomic particles (e.g., electrons, protons, neutrons, etc.). Thus, the radioactive nuclear waste never impacts the sun, having no effect upon its “ecosystem,” and therefore cannot “damage” the sun.

• @Mark heavier atoms might not have "structural integrity" under those conditions, but the nuclei do (at least until they get deep enough to undergo fission) – Robert K. Bell Jul 22 '20 at 9:02
• @RobertK.Bell That makes more sense yeah, the text mentions subatomic particles though, and specifically protons and neutrons – Mark Jul 22 '20 at 9:08
• I like how they labelled "nonrecoverable" as a downside to ejecting waste from the solar system, but not to chunking it into the sun – Asteroids With Wings Jul 22 '20 at 10:32
• It's not recoverability of the waste. It's recoverability of the launch vehicle so that it can be re-used. – JdeBP Jul 22 '20 at 12:05
• @TannerSwett I think I agree with Mark; there's really nothing preventing heavier nuclei from existing in stars. Carbon, nitrogen and oxygen are the main metals in most stars, and play a key role in fusion for stars at least several times the Sun's mass, via the CNO cycle. The strong nuclear force is strong enough that collisions are unlikely to break apart nuclei. (Also, Andrew, excellent answer - I upvoted last night but didn't get the chance to comment!) – HDE 226868 Jul 23 '20 at 0:59

# "Waste" is Fuel

Radioactive waste is fuel. We just call it "waste" because we have primitive thermal neutron reactors which are very picky divas and demand fairly enriched U235 (well, if you count 3% as "fairly enriched", which it is, compared to the natural composition). In fact, current LWR reactor technology only "burns" about 1% of the uranium in a fuel rod, leaving 99% of the fissionable material. On the other hand, fast neutron reactors can "breed" more fuel than they consume by transmuting the normally useless U238 into P239. They can also transmute thorium, making it a nuclear fuel source. In general, fast neutron reactors can "burn" just about all the long-lived radioisotopes which occur or result from commercial fission reactions. The only question is how much energy you want to extract.

# Breeding, Burning, Garbage Disposal

A fast breeder reactor can produce fuel while also producing useful energy. India's nuclear program is predicated on the idea that you can use a small stockpile of enriched uranium to bootstrap an entire nuclear industry that ultimately runs on thorium (of which India has abundant supplies). Whereas, thermal neutron reactors exclusively "burn" the easy fuel. If you are willing to forego some of your power generating capacity, you can essentially make a fast breeder reactor burn all its fuel, which will get rid of more than 99% of the nuclear waste you can produce.

In this mode, the reactor will not be as efficient, because unproductive daughter products will build up, poisoning the chain reactions. Even so, the constant bombardment of neutrons will force the daughter products to fission down to a small handful of products which are far more easily managed.

Note that some of the fission products are commercially valuable, such as Krypton-85 (no, not to defeat Superman), Strontium-90, and Caesium-137.

• You know, I'd always heard the term "breeder reactor" and kind of understood the concept, transforming nuclear material into something more useful. But your description made it a much clearer concept in my mind. Thanks! – Ruadhan Jul 22 '20 at 8:15
• That said, I'm not sure this really addresses the question, it's more of a Frame Challenge – Ruadhan Jul 22 '20 at 8:18
• @LawnmowerMan that is not so. Would it be - there would be no such a thing as residual heat" and "spent fuel pools". Decay is multistage process. Fuel is spent, when siginificant share of 235-U fissiled, and the heat output becomes too low for business profits. But it does not mean ALL of 235-U spent. Crypton, Cesium, Iodium - fissiel isotopes of those are created in large numbers all through the fuel cells. And they continue decay for years to come. Would it be other way - there will be zero problem to through spent nuclear fuel in usual city landfills, alone with broken bottles and paper. – Arioch Jul 22 '20 at 17:50
• @DanielR.Collins They're not that theoretical. One was built almost half a century ago, and ran for more than a year: en.wikipedia.org/wiki/THTR-300. The BN-600 and -800 are still running: en.wikipedia.org/wiki/BN-600_reactor, en.wikipedia.org/wiki/BN-800_reactor. Even India has an operational reactor: en.wikipedia.org/wiki/Fast_Breeder_Test_Reactor. The only reason we don't have them running now is due to politics and cost, not science. – Lawnmower Man Jul 22 '20 at 19:51
• Those hypothetical "burners" - working at loss, similar to garbage incinerator "factories" - would have to get transportable fuel, that means - the fuel that already was cooled down for years and years after being "spent" in [conventional] reactor. If we will return to my initial comment, it was exactly about that: you can not transport "spent fuel" you just pulled out of energy generating reactor. You have to keep it ever-cooled and isolated from any living things for years and years, before it becomes "just dangerous" and can be transported anywhere. – Arioch Jul 23 '20 at 10:48

Economically it is less expensive to shoot a rocket into deep space and more expensive to send it to the sun.

It is even less expensive to crack the waste down and recycle it, by far. For the billions you have to invest in a repeating sunward launch, you can research, engineer and build a transmutation reactor instead and gain lots of value from the waste.

Finally, when you start to put strange things into the sun, it's like signalling. Under the assumption that there are aliens and they watch with good spectroscopes, they could maybe see it. So if your universe is hostile, that can be a danger in itself. I don't know if that signal is stronger than our radio emission, though. Probably not.

My main point is, sending stuff to the sun is just super duper expensive. Basically everything else is cheaper, even sending stuff away from the sun.

• Your third paragraph needs some calculations to back it up. I suspect it is not true. See the answer by Andrew Brēza: the stuff wouldn't even be hazardous waste anymore by the time it would reach the Sun. – gerrit Jul 22 '20 at 7:30
• As HDE 226868 explained in the comments of his answer, I think it's not unreasonable to assume some changes could (emphasis on the conditional) be detected. – ThePainfull Jul 22 '20 at 7:39
• You say "expensive" as in refering to money. But i wonder, if we touch the issue of being cost effective, which the topic starter explicitly wanted to ignore, if the orbital launch itself would generate more waste, that it lifts away. Would "net total" of "dumpster launches" decrease or increase amount of waste on Earth? – Arioch Jul 22 '20 at 10:36
• @Arioch, actually, when Anderas refers to "expense", I suspect he's referring to orbital mechanics. Most people think that because of gravity, all you have to do is point a rocket in the general direction of the sun and it will get "sucked in." Untrue! Orbital mechanics are a lot more tricky than that, and it takes more energy to get a projectile from a planet to the star it is orbiting than virtually any other set of orbital maneuvers. However, you're not entirely wrong, because energy amounts are proportional to amount of fuel, and greater amounts of fuel generally cost more in money. – Forbin Jul 22 '20 at 12:56
• @Arioch Yes, you don't need to shed all orbital speed around the sun in order to hit it. But you need to shed almost all of it. More precisely, you need to enter a highly elliptical transfer orbit that has its lowest point just above the sun's surface where the drag in the corona will suffice to turn your spaceship into plasma. There are actually easier ways to reach the sun, either by playing slingshot with Jupiter etc., or by going the other way first and then decelerating when you are somewhere past Pluto. The later brings the $\delta v$ down to a little over $12.3km/s$. – cmaster - reinstate monica Jul 25 '20 at 21:09

The sun currently contains about a Jupiter mass of iron, left over from its formation.

Putting the entire Earth into the sun would not affect its lifetime significantly.

• I don't disagree with the answer, but I don't think it really supports its conclusions. All the first sentence establishes is that stars can have non-zero metallicities, not that changing those metallicities will cause noticeable differences. Maybe it's just a bit of a nitpick, but it would be nice to address the OP's specific question. – HDE 226868 Jul 21 '20 at 22:44

Jupiter, while not a star, sucks up asteroids and such all the time with no major impact. Considering any trash heap you might drop into the Sun is basically a glorified asteroid and the Sun is about 1000x more massive than Jupiter, you probably won't even notice a difference.

• Plus: Jupiter is much easier to reach than the sun. And it does not have a solar wind that might carry the waste back to you. – cmaster - reinstate monica Jul 24 '20 at 16:35

• Jupiter is much more easy to reach with a rocket

• Jupiter does not have a solar wind that might carry your waste back to you

• Jupiter is a gas giant without strong convection

The last point is relevant because it means that your heavy nuclear waste will simply sink into the planet and remain there. The perfect end storage solution.

If you are already committed to dumping your waste in space, Jupiter is the place to send it. It still needs a lot of effort to reach, but there is no safer and easier destination in space than that.

• Do we know a lot about Jup's core? Can it be dense and hot enough to start fission? And then, maybe, start fission-fusion mutual boost ? – Arioch Jul 27 '20 at 8:44
• @Arioch To start fission, you don't need temperature, you need free neutrons, and a small enough geometry to avoid loosing too many neutrons before they escape the fissile material. Afaik, the core of Jupiter is hypothesized to consist of mostly hydrogen which is as non-fissile as it can get. There may also be heavier stuff, like an iron core. But whatever there is, nuclear waste is generally not enriched to levels that can start a chain reaction at all, it catches too many neutrons without splitting. – cmaster - reinstate monica Jul 27 '20 at 9:12
• By fissile material i mean the dump from Earth. Can hydrogen act as neutrons moderator? Water can... Nuclear waster can not be burn in light water reactor, but even on Earth it still can be burn further in fast neutron breeders... – Arioch Jul 27 '20 at 9:49
• @Arioch Yes, hydrogen acts like a moderator just the same as water, it's the nuclei of the hydrogen atoms in the water that collide with the neutrons to take away their energy. For burning nuclear waste, you need a fast neutron reactor which does not moderate the neutrons as quickly as water does. So, it's exactly the opposite conditions which you would need to start a chain reaction. Also, even fast breeding reactors need fuel processing to remove neutron capturing waste and they need a certain starting concentration of fuel that has already been bred. – cmaster - reinstate monica Jul 27 '20 at 11:00
• Sure, but moderated neutron reactor is much easier to kickstart. Tokaimura'97. And there was one ancient river in Africa AFAIR, where reactor was built even without mankind. Nothing of a kind without moderation, right? So i would suppose fast-neutron fission is indeed nigh impossible in Jupiter, but i would not be so sure about moderated one... – Arioch Jul 28 '20 at 8:31

If one is ready to spend THAT MUCH on disposing off some kind of waste, this begs the question how much dangerous is the waste in the first place.

As of now, the most dangerous waste we produce is the spent nuclear fuel and/or its reprocessing tails.

Probably equally bad are some highly reactive or poisonous chemicals.

In fact, we already have a means of managing it safely on Earth. Not that we always do, but it will still be cheaper (and pretty much more sustainable) than using rockets to move it to space (and even larger rockets to get it to the Sun). Rockets have their own eco implications, we are okay-ish with them because we don't use them much (compared to, say, automobiles).

Since you are talking about other stars - depending on your star and other planets in your system, it may be, unlike our Sun, easier to reach the star rather than the deep space.

What's more, in most cases it is generally better to keep some form of exotic waste until it happens to be a resource. The history of mining industry knows a lot of cases when a bug pile of waste that no one wants suddenly becomes a valuable resource and people start reprocessing it.

Then again, the technology moves forward and we constantly invent more and more unpleasant forms of waste. How about https://en.wikipedia.org/wiki/Strange_matter ? If it is able to convert the ordinary matter into itself, it will be equally bad (or even worse) at the Sun - instead of killing a single planet it will kill the solar system (probably later, so open to smuggling and corruption).

• "As of now, the most dangerous waste we produce is the spent nuclear fuel and/or its reprocessing tails." I disagree. Some hot metal that just needs to be stored away from children and animals is far less dangerous than CO2 spilled into the atmosphere and altering our climate! : ) – Grimm The Opiner Jul 23 '20 at 9:52
• CO2 is bad, but to remove it from the Earth completely is probably even worse. We'll need to feed our plants and algae even after we solve the stupid energy puzzle. Not to say that the most efficient technology for CO2 collecting as of now are plants and algae themselves. And for 1 ton of CO2 on LEO (that's enough, sun wind will blow most of it away from Earth) you'll get 1000s of tons as a rocket exhaust. Not a great deal, is it? – fraxinus Jul 23 '20 at 10:04
• "CO2 is bad, but to remove it from the Earth completely is probably even worse" Probably? Only probably..!? : D Without CO2, we would all actually stop breathing! – Grimm The Opiner Jul 24 '20 at 7:03
• It will take way more energy to send the (excess, to get back down to 300 ppm) CO2 to space than was released in the fossil fuel burning it. Rockets that go to orbit are only ~5% payload and mostly fuel. Once we cover the Sahara with solar panels why not just turn it into graphite and bury it? – Kevin Kostlan Jul 24 '20 at 16:15
• @GrimmTheOpiner driving the concentration of CO2 down enough to interfere with human breath is even harder task and will probably be equally bad for climate. I think returning to those 280-300ppm of my childhood is enough. Sort of. – fraxinus Jul 24 '20 at 18:49

As others have said, the sun can take anything. However, dumping waste in the Sun requires us to cause a lot of environmental devastation on Earth in order to collect the resources for this enterprise; Since not of all the waste will go to the Sun, this process is not sustainable.

In order to make this work, we would need some magical technology (in the Clarkean sense: something so advanced we could not comprehend it today) that would zero out the costs of sending stuff to the Sun.

One aspect I don't see addressed in the answers here with regard to safety is the mass from Earth you lose by doing this. Yes, garbage -- and especially nuclear waste -- is presently a challenge for us now, but destroying it by sending it into the sun negates the potential for future technology to turn such garbage into useful material.

If we were to send all of our garbage to the sun, the Earth's mass would gradually decrease as we exhaust natural resources assembling materials that are used, discarded, and fully destroyed/burnt. So, in essence, we trade the problem of where to store garbage we want to discard for a problem of losing mass that could be useful in the future. Do it over several centuries and I'd imagine the mass lost would be sizable.

• Each year we produce waste for 2.13e-13 the mass of Earth. We would be extinct before we even make a dent. – L.Dutch - Reinstate Monica Jul 22 '20 at 13:21
• We waste disproportional amount of the Earth constituents. – fraxinus Jul 23 '20 at 15:22

You can toss anything into the sun, at 2.6 Million degrees in the convection zone anything tossed inside will be totally incinerate, course that'll happen before it reaches the photosphere anyway

Imagine every 1000th launch failing and dispersing garbage all over the launch area or populating near Earth orbit with fast moving projectiles.

• This is not what the OP is asking – L.Dutch - Reinstate Monica Jul 31 '20 at 2:45
• Author asked if it was safe. I pointed out that it wasn’t. – Konrads Jul 31 '20 at 10:40

Two issues only;

1. Cost (specifically launch costs), it has to be cheaper than processing (or storing ) the waste in question on Earth. This is unlikely at least for the foreseeable future.

2. Launch safety; Technology fails, some types more often than others. Depending on how toxic/dangerous the material you are launching is (and how much of it there is) you need rockets/rail guns etc with an extremely high level of reliability. Which, as noted above is expensive.