Minimum safe distance from a supernova?

[Quartz]

You are standing in a spacesuit on a 100 km diameter rock orbiting a star of 10 solar masses. The rock is tidally locked to the star. The star has no companion. The star explodes in a supernova. There is no gamma ray burst. How far away from the star for you to survive does the rock have to be if you are on the near side of the rock? How about the far side?

[running_coach]

30 light years isn’t enough.

… were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.

[Quartz]

@running_coach

30 light years isn’t enough.

That’s a whole different kettle of fish, one which is not relevant to my OP.

[Dr.Strangelove]

A supernova is about 10 billion times brighter than a star. The sun is comfortable at Earth’s distance, but if it were 10 times brighter it would be lethal in a normal spacesuit–you’d quickly overheat. So you need to be at least sqrt(1000000000) = 32,000 AU away, or about half a light year. I think I might want the full light year for a bit more comfort.

In related news, you’ll get a lethal dose of neutrino radiation poisoning at 2.3 AU.

[Gray_Ghost]

This guy, Michael Richmond, crunched a lot of the numbers for you. Original page doesn’t work anymore, hence the archive.org link.

Highlights:

“This is significant – a type Ia SN, at the distance of 1000 pc, dumps as much gamma-ray radiation onto the earth as 1,000 solar flares.”

“Conclusion: I suspect that a type II explosion must be within a few parsecs of the Earth, certainly less than 10 pc (33 light years), to pose a danger to life on Earth. I suspect that a type Ia explosion, due to the larger amount of high-energy radiation, could be several times farther away. My guess is that the X-ray and gamma-ray radiation are the most important at large distances.”

[levdrakon]

If you’re close enough to be tidally locked, you’re probably in the supernova.

[Quartz]

@Gray_Ghost

This guy, Michael Richmond, crunched a lot of the numbers for you.

Guys, for this thread I’m not interested in the effect of life on Earth; I am interested on the astronaut in the spacesuit on the rock.

[Quartz]

@Dr.Strangelove

A supernova is about 10 billion times brighter than a star. The sun is comfortable at Earth’s distance, but if it were 10 times brighter it would be lethal in a normal spacesuit–you’d quickly overheat.

But isn’t a supernova a near-flash or wave which quickly passes you? A camera flash is from hundreds of thousands to millions of lumens.

So you need to be at least sqrt(1000000000) = 32,000 AU away, or about half a light year. I think I might want the full light year for a bit more comfort.

How about being on the far side of the rock?

In related news, you’ll get a lethal dose of neutrino radiation poisoning at 2.3 AU.

Rocks don’t protect against neutrinos, so adding a fudge factor for safety we’re looking at a distance of Jupiter for neutrinos.

[Quartz]

@Gray_Ghost

This guy, Michael Richmond, crunched a lot of the numbers for you.

I’m sorry; I should have read further:

@Michael Richmond

Following the measurements of the type Ib/c SN 2008, we can estimate the danger from the prompt X-ray emission due to the shock breakout. The peak luminosity in X-rays was about 6 x 10^(43) erg/sec, and the breakout lasted about 400 seconds, so that’s a total of about 2.6 x 10^(46) ergs. Plugging into the formulae above, we find that this prompt X-ray dose would reach the lethal level (300 rems) if the SN was about 300 pc or closer.

That’s insane. But then we’re dealing with insane energies.

[ftg]

@Dr.Strangelove

In related news, you’ll get a lethal dose of neutrino radiation poisoning at 2.3 AU.

The “supernova at 1AU vs H-bomb against the eye comparison” is one of my all time favorites.

[chorpler]

@ftg

The “supernova at 1AU vs H-bomb against the eye comparison” is one of my all time favorites.

Especially the illustration and its popup text, which says “Can you hurry up and set it off? This is heavy.” After reading that, I suddenly noticed the “motion lines” around the bomb, which are clearly intended to convey the impression that the poor stick figure is trembling while struggling to hold that thing up against his eye.

[chorpler]

@Quartz

Rocks don’t protect against neutrinos, so adding a fudge factor for safety we’re looking at a distance of Jupiter for neutrinos.

(Warning: both links below are directly to PDF files)

That may be a little close, since the “What If?” article uses results from Andrew Karam’s calculations, and in the referenced paper, Karam says:

This level of radiation exposure [from 5MeV and 15MeV neutrinos at a distance of one parsec] is trivial and will not be considered further. The biological effects of neutrinos have received some attention (Collar 1996; Cossairt and Marshall 1997; Cossairt et al. 1997), although these dose calculations did not include the expected neutrino energy spectrum used here. While the details of the effects are a matter of speculation, at this low level of dose equivalent, they must be completely insignificant.

And, you know, if you’re just talking about distance-of-Jupiter instead of parsecs, something completely insignificant could become significant…

(The paper by Collar can be found here. I couldn’t find a copy of the Cossairt and Marshall comment on his paper, nor his reply to them, that wasn’t behind a paywall.)

[watchwolf49]

I think it’s safe to say that any rock orbiting the star before it goes supernova would be toast … standing on the far side is of little protection if your rock is suddenly vaporized … even the furthest reaches of the planetary system would be bombarded with solar innards … an iron atom traveling at the speed of light packs a punch … and we’ll have a gaggle of heavy atoms hitting us …

We’d be better off orbiting the next star over …

[Chronos]

Quoth Quartz:

But isn’t a supernova a near-flash or wave which quickly passes you?

“Quickly”, in this context, means a few months.

[Quartz]

@watchwolf49

We’d be better off orbiting the next star over …

And even that might be too close.