# How much advance notice does an at-risk planet have for a supernovae? **URL:** \ **Category:** Factual Questions\ **Created:** [May 11, 2009, 8:57pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086 "2009-05-11T20:57:16Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![filmore](https://avatars.discourse-cdn.com/v4/letter/f/7993a0/32.png) [@filmore](https://boards.straightdope.com/u/filmore)\ **Post date:** [May 11, 2009, 8:57pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/1 "2009-05-11T20:57:16Z")
In a recent blockbuster movie, a planet is destroyed by a nearby star going supernovae. Seemingly, there was very little notice. Is that likely? Could you have a star close enough to destory a planet, yet the people on the planet not know it’s going supernovae until it’s too late? Wouldn’t there be an abundance of signs of the impending doom? ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 11, 2009, 9:25pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/2 "2009-05-11T21:25:34Z")
Short answer: no. First off stars are not very old when they supernova and no life could possibly have evolved on planets there. Or no multi-cellular life, if the earth is at all typical (a matter of 2 billion years). I suppose two older stars could have collided and produced a supernova star. But any inhabitants who evolved on one of the stars would have fried almost immediately. If you think interstellar colonization is possible (as in my namesake), then if they colonized a distant planet of an unstable star, they would know immediately from the mass of the star that it would one day become unstable. Whether they would know to within some thousands of years is another question, but my guess is that they by studying the spectrum, neutrino emission and so on, they would have warning. Anyway, there would have to be damn good reason to colonize it. Maybe an anti-agathic drug grows there. Maybe it is paved with gold–or diamonds. ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [May 11, 2009, 10:03pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/3 "2009-05-11T22:03:01Z")
I remember reading somewhere that you wouldn’t have to be on a planet orbiting the supernova to be in danger - if a supernova goes off anywhere within ten light years of the Earth (maybe even further away), we’re toast. Is there any truth in this? ---
**Author:** ![Toolie](https://avatars.discourse-cdn.com/v4/letter/t/41988e/32.png) [@Toolie](https://boards.straightdope.com/u/Toolie)\ **Post date:** [May 11, 2009, 10:19pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/4 "2009-05-11T22:19:39Z")
A tangential (but slightly related) question I’ve always had: Suppose there was a gamma-ray burst somewhere in the vicinity of our solar system, showering the earth in high energy gamma rays. Would only half of the earth suffer the effects, and the side facing away from the GRB have it’s biosphere survive pretty much intact? ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [May 11, 2009, 10:51pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/5 "2009-05-11T22:51:12Z")
> [@Toolie](#): > > A tangential (but slightly related) question I’ve always had: > > Suppose there was a gamma-ray burst somewhere in the vicinity of our solar system, showering the earth in high energy gamma rays. Would only half of the earth suffer the effects, and the side facing away from the GRB have it’s biosphere survive pretty much intact? I recommend former SDMBer **The Bad Astronomer** ’s new book, **Death From the Skies!** , for questions like this. He goes into great detail on supernovae and gamma-ray bursts. Essentially, no, it would be a global catastrophe. Gamma-ray bursts, being beamed phenomenon, can be deadly from far away; a GRB from 100 light years away “would be like blowing up a one-megaton nuclear bomb over every square mile of the planet facing the GRB. It’s (probably) not enough to boil the oceans or strip away the Earth’s atmosphere, but the devastation would be beyond comprehension,” according to chapter 4 of my ebook version. For the rest of the planet, there would be an EMP that would basically destroy the power grid and most of our electronic equipment, which would probably destroy civilization; the ozone layer would be destroyed on the side of the earth facing the GRB and would be depleted by 35-50% overall, leading to lots of damaging UV light getting through to fry plants and plankton and microbes; nitrogen dioxide would likely significantly reduce sunlight getting through to the earth, resulting in a global cool-off possibly steep enough to trigger a new ice age, plus lots of acid rain would fall… Oh, and the cosmic rays produced in the GRB would arrive a few hours later; even a GRB 7500 light years away would result in cosmic rays that would cause a muon shower that would give almost all the humans in that hemisphere about ten times a lethal dose of radiation, and “Hiding won’t help much; muons can penetrate water to depths of more than a mile and also go right into rock down to depths of half a mile! This would therefore affect nearly all life on Earth.” Since those particles travel slower than light and therefore impact some time after the initial gamma rays, the earth’s rotation between the time of the initial gamma ray strike and the cosmic ray strike would mean that even MORE of the planet would be blowtorched. ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [May 11, 2009, 11:16pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/6 "2009-05-11T23:16:13Z")
> [@Alive\_At\_Both\_Ends](#): > > I remember reading somewhere that you wouldn’t have to be on a planet orbiting the supernova to be in danger - if a supernova goes off anywhere within ten light years of the Earth (maybe even further away), we’re toast. Is there any truth in this? Probably. **Death From the Skies!** says, in the chapter on supernovae, that a supernova that would destroy the ozone layer badly enough to wipe out the bottom of the food chain if it were within 25 light years (possibly within 100 light years depending on which extreme you take). So there’s at least that. On the other hand, Charles Sheffield wrote a pair of novels ( **Aftermath** and **Starfire** ) about _freaking Alpha Centauri A_ going supernova, only 4.3 light-years away, and while it knocked human civilization down and out, it didn’t kill us off by any means. Granted, it’s fiction, but Sheffield was a physicist and the books went into great detail about the effects of a supernova so close to earth, and it wasn’t even a human-extinction event. I’m not sure how Sheffield figured out how bad it would be … but **I’m** certainly not going to be the one to flat-out say that Charles Sheffield got it wrong! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 11, 2009, 11:44pm UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/7 "2009-05-11T23:44:58Z")
> [@](#): > > "Hiding won’t help much; muons can penetrate water to depths of more than a mile and also go right into rock down to depths of half a mile! Which is precisely why you shouldn’t worry about muons. Anything that can get through that much water without significant interaction can also get through you without significant interaction, and if it doesn’t interact with you, who cares? One other danger from a nearby GRB, incidentally, is that it would burn much of the atmosphere into nitrogen oxides, some of which are opaque. They’d break down in time, but not quickly enough to prevent a “nuclear winter”-type scenario. ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [May 12, 2009, 2:06am UTC](https://boards.straightdope.com/t/how-much-advance-notice-does-an-at-risk-planet-have-for-a-supernovae/496086/8 "2009-05-12T02:06:34Z")
> [@Chronos](#): > > Which is precisely why you shouldn’t worry about muons. Anything that can get through that much water without significant interaction can also get through you without significant interaction, and if it doesn’t interact with you, who cares? It interacts with you enough that a sufficient number of them will kill you, and a close-enough GRB will produce enough to get the job done. At least, according to Phil and his sources. The complete paragraph is: > [@](#): > > From **Death From the Skies!** , chapter 4: > Then there’s the issue of subatomic particles (cosmic rays) from the burst. It’s unclear just how damaging these would be from a GRB. But, as discussed in chapters 2 and 3, high-energy particles may have all sorts of effects on the Earth. A GRB from 7,500 light-years away would inject a vast number of subatomic particles into our atmosphere, and they would be moving at just a shade under the speed of light. Within hours of the initial burst they would slam into the air, creating a shower of muons. We see muons coming from the sky all the time, but in small amounts. From a nearby GRB, the number of muons generated would be huge. One team of astronomers calculated that as many as _300 billion per square inch_ could hit the Earth’s surface all over the hemisphere facing the blast. If that sounds like a lot, well, it is. These particles would cascade down from the sky and be absorbed by anything out in the open. Given how well human flesh can absorb muons, the astronomers who did the calculation found that the energy absorbed by an unprotected human would be ten times the lethal dose. Hiding won’t help much; muons can penetrate water to depths of more than a mile and also go right into rock down to depths of half a mile! This would therefore affect nearly all life on Earth.