往太空里投一枚核弹，会发生什么？｜科学60秒

1962年7月9日“多米尼克行动”（Operation Dominic）中

“海星一号”高空核试验爆炸的照片

图片来源：U.S. Air Force 1352nd Photographic Group, Lookout Mountain Station - Image courtesy of US Govt. Defense Threat Reduction Agency, Public Domain

Unfortunately it seems like some folks may disagree. The United States Department of Defense has sounded the alarm on a potential threat from Russia in the form of a hypothetical program aimed at putting a nuclear weapon into orbit. While there’s no evidence that such a device is on its way into space, let alone already up there, I think it’s safe to say we’d all rather be sure that Russia, like, definitely wasn’t going to do that.

But let’s not get ahead of ourselves—what actually happens when a nuke goes off in space? Thanks to the hubris of humankind, that’s a question we can answer from experience.

For Scientific American’s Science Quickly, I’m Rachel Feltman. Associate news editor Allison Parshall is joining me today to tell us more.

So, Allison, what are we talking about when we talk about nukes in space?

Allison Parshall: Yeah, it’s definitely worth being specific. But, like, what we’re talking [about] is specifically about nukes in orbit. I mean, there’s also the question of nuclear power in space. We power satellites with nuclear power. There’s some fun tales—and by fun, I mean distressing—from, you know, the 1960s and 1970s about attempts to power satellites with nuclear fuel.

In 1978 a Russian satellite that was powered by a nuclear reactor failed, and debris fell— scattered over Canada. So that was fun. But if we’re talking specifically about nuclear weapons positioned in orbit to potentially be exploded in orbit, that’s, like, a whole separate question.

That’s not something that we’ve necessarily had before, and it would be super bad. So let’s not do it.

Feltman: Yeah, no—100 percent agree. I think we can all safely end up on the same side of that debate. So what is the difference between a nuclear explosion on Earth and one in space?

Parshall: Yeah, I mean, we’re really familiar with what a nuclear explosion would look like on Earth, right? Like, we have the—the United States dropped bombs on Hiroshima and Nagasaki in 1945, killing over 200,000 people, and we’ve had hundreds of nuclear weapons tests since. And you’ve probably seen what this looks like in movies and TV shows—you know, Fallout, Oppenheimer, Dr. Strangelove.

You’ve got that first fireball that just kind of vaporizes everything around it within a certain radius. That fireball causes a shock wave that can be really devastating: It can level buildings. It can start firestorms. And then both of those things result in the really famous, distinctive mushroom cloud that erupts over where the bomb was dropped. And then, of course, you have the thing that is probably really concerning in the long term, which is the nuclear fallout.

You’ve got all of that radiation that lingers for decades. It can kill in minutes, or it can kill in decades. And in space almost none of this happens because we’re in somewhere with very little atmosphere, so there can'’ be a fireball, there can’t be a shock wave, and there can’t be a mushroom cloud.

Feltman: Mm-hmm.

Parshall: So what you get instead is just so much radiation spewing out from the explosion. You get that radiation in the form of gamma rays and x-rays, and those can travel really far because, like I said, there’s little to no atmosphere to interfere with them.

Feltman: Mm-hmm.

Parshall: We know that satellites in the line of sight would be damaged or taken offline entirely by that initial blast.

It would create an electromagnetic pulse that would fry unshielded electronics within a certain radius on Earth and in space. And perhaps most concerningly, we know that we would get this belt of radiation that is similar to something called a Van Allen belt.

A Van Allen belt exists naturally in space—satellite operators try to avoid having their satellites go through them because it can damage them. This artificial belt of radiation loops out from the Earth, and it can last for years.

Fetlman: Wow. Okay, so, uh, not great—something worth avoiding. So how do we know that this is what would happen if it’s so bad and worth avoiding?

Parshall: I’m glad you asked. This is a fascinating story. I did not know about this before I started reporting on it. I kinda can’t believe I didn’t know about it. But basically we tested this—by we, I mean humanity—the hubris of humanity...

Feltman: Of course we did.

Parshall: The U.S. and the Soviet Union conducted over a dozen high-altitude tests of nuclear weapons between 1958 and 1962. The most famous of them—I guess the most notorious, you could say—was called Starfish Prime. It happened on July 8, 1962, at 11 P.M. local time, relative to Hawaii. It launched on a missile from Johnston Atoll, which is in the middle of the Pacific, not too far from Hawaii.

It was detonated 250 miles above the Earth’s surface. So that’s low-Earth orbit. It’s where most satellites orbit today. It’s where the International Space Station orbits today. And this bomb was 100 times stronger than the one the U.S. dropped on Hiroshima.

Feltman: Wow. Why?

Parshall: Why? I mean, to test.

Feltman: To see what would happen—okay, sure.

Parshall: Yeah, to see what would happen. I mean, it’s relevant now. But it’s interesting—people in Hawaii knew that this was going to happen. There are newspaper headlines from before the test that advertised the, quote, “n-blast” would be “dazzling” and that people might have a “good view,” and people did have a good view.

Feltman: Wow.

Parshall: And it seems like it was dazzling. The people who saw this from the Pacific describe auroras that are just unlike anything that I’ve ever heard described. Basically the radiation from the blast excites molecules in our upper atmosphere, and depending on what those molecules are, you get different colors. And so accounts say that when the blast first happened, there was this startling flash of green that kind of lit the sky up like daylight, even though it was 11 P.M.

And that green kind of faded to yellow, to orange and then settled on this eerie red. There’s really startling pictures. I would recommend looking them up.

Also, the electromagnetic pulse it generated knocked out about 300 streetlights in Oahu. And it doesn’t seem like the scientists really expected any of this to happen.

I mean, they certainly knew some of it—this was not the first test. But it seems like the strength of it took scientists by surprise, as well as that belt of radiation that lingered for years. It also killed about a third of the satellites that were in orbit. It’s nothing compared to the number we have now.

It was maybe, like, two dozen satellites, about eight of which were killed or damaged. That included one called Telstar 1 that launched the next day after Starfish Prime. That thing got 100 times more radiation than they expected, and it was toast.

Feltman: Oh, wow.

Parshall: Yeah. And a source I spoke with—his name is Jonathan McDowell at the Center for Astrophysics | Harvard & Smithsonian—he called Starfish Prime the, quote, “poster child for why we don’t like nukes blowing up in space,” which, I think, is a fair summary.

Feltman: That seems fair.

Parshall: Yeah, and we know that the governments that were doing these kind of decided we shouldn’t be doing this anymore because both the U.S. and the U.S.S.R. signed on to the Outer Space Treaty in 1967, five years later, which forbade putting nuclear weapons—or really, more generally, weapons of mass destruction—into orbit.

Feltman: Yes. Speaking of that treaty, if I’m understanding correctly, it’s not totally clear how seriously Russia is considering putting a nuclear weapon into orbit—if they’re considering it at all.

But some government officials in the U.S. certainly were concerned enough to talk about it publicly. So what’s the actual worst-case scenario here?

Parshall: Yeah, I mean, I definitely is not clear the extent to which they’re seriously doing this. One of the sources I spoke with said that, you know, this could just be a PowerPoint from some general, or it could be a serious program. But it might not necessarily be a serious program designed for them to actually—endgame—detonate a nuke in space.

The State Department said that there was no, quote, “imminent threat.”

So I don’t want people to be afraid of a nuke off above their head. But, yeah, if this happened, it would be bad. Geopolitically it’s the kind of thing that we spent a lot of the cold war worrying about—just very escalatory. Of course, you worry about those tensions escalating even further into more nuclear exchanges and global thermonuclear war—don’t want that.

Feltman: Yeah, would love to avoid.

Parshall: But as far as the direct effects of what you’d see if this went off today, like I mentioned, it would be worse because there’s more things in space now than there were in 1962. We have 10,000-ish satellites in orbit. Most of those are in low-Earth orbit. We’ve got two space stations.

Of those 10,000 satellites, 6,000 of them are Starlink satellites. Depending on the height and the strength of the blast and where it went off, you could expect a lot of those to be damaged or killed. They would effectively be turned into space junk—just aimlessly floating without a real way to recover them.

And it’s not just inanimate satellites that we’re worrying about. There are people in space. There’s people on the International Space Station and China’s Tiangong space station. An electromagnetic pulse from a nuclear weapon going off could mess with vital systems aboard. It could also leave the astronauts to be navigating a bunch of space junk, which could potentially harm the space stations.

And the radiation itself, depending on where the blast went off, could be really directly harmful. I spoke with Victoria Samson. She works for the space sustainability [organization] Secure World Foundation. And she said that a nuclear blast in orbit could limit the safety of people on these space stations to mere hours or days.

And she was citing this 2010 Department of Defense report. They tested 17 possible scenarios—worst-case scenario showed...[full transcript]