Gamma-ray shielding against bursters

[Rynn]

Thinking about the crashcache back up, how deep do you think something could be safely floated in a gas giant with OA tech? Obvious follow up being is said depth enough protection against GRBs?

[Cray]

Thinking about the crashcache back up, how deep do you think something could be safely floated in a gas giant with OA tech? Obvious follow up being is said depth enough protection against GRBs?

Earth's atmosphere is pretty good at stopping the gamma rays from a burster. Further, the primary effect is to crash the ozone layer, not flash-fry the surface with lethal rads.

I'm not sure how a gas giant's hydrogen-helium atmosphere compares, but since enough mass should block energetic photons like anything else I'd guess those gases are on par with Earth for a given areal mass of atmosphere. Of course, a hydrogen-helium atmosphere has about 1/10th the molecular mass of Earth's atmosphere.

Therefore, somewhere in the vicinity of 5 to 10 atmospheres pressure in a gas giant should provide adequate shielding. On some gas giants, that's a quite comfortable level for humans. Bubblehabs, never mind crashcaches, would be fine.

[selden]

Some tiny fraction of extrasolar gamma rays do penetrate the Earth's atmosphere all the way to the surface. Extrasolar GRBs were first detected by military satellites looking for the gamma rays emitted by nuclear bomb testing. If some fraction can escape through the atmosphere, the same proportion can also come down through that same depth of atmosphere.

If a GRB happens close enough, that tiny fraction is going to be very large in absolute terms.

[Bear]

Cray has a point though. 3km of rock is insane, whether you're talking about particulate or electromagnetic radiation.

A GRB is a planet-sterilizing event in the long term, but at even moderate interstellar range it wouldn't be lethal in a single generation. It would take a while for the mutation load to build up faster than repair or selection could handle, for weak links in the biosphere to go extinct depriving others of food, etc. Eventually even the most shielded things would succumb, but not due to radiation; If they're shielded, they'd die out due to the crashing biosphere around them. The amount of radiation we're talking about at surface level is not compatible with life in the long run, but needing more than 10m of rock for shielding would imply the surface getting flash-fried.

[Drashner1]

A GRB is a planet-sterilizing event in the long term, but at even moderate interstellar range it wouldn't be lethal in a single generation. It would take a while for the mutation load to build up faster than repair or selection could handle, for weak links in the biosphere to go extinct depriving others of food, etc. Eventually even the most shielded things would succumb, but not due to radiation; If they're shielded, they'd die out due to the crashing biosphere around them. The amount of radiation we're talking about at surface level is not compatible with life in the long run, but needing more than 10m of rock for shielding would imply the surface getting flash-fried.

A bit of googling seems to indicate that the nearest potential GRB is about 7500-8000ly away. And that if it went bang, it could mess with our ozone layer, but not cook the planet or the like (if the beam is actually aimed at us).

Applying this back to the OA universe, this distance puts it just inside the Periphery. So some kind of expedition could be there or on its way to modify the star to remove the threat (possibly by removing the star entirely).

As far as dealing with a GRB actually hitting a planet (since in Y11k, there are many more planets than just Earth to deal with), OA tech could effectively undo or prevent the negative effects quite rapidly, essentially healing the entire biosphere in a matter of decades (or faster if transapients were involved).

Todd

[Cray]

As far as dealing with a GRB actually hitting a planet (since in Y11k, there are many more planets than just Earth to deal with), OA tech could effectively undo or prevent the negative effects quite rapidly, essentially healing the entire biosphere in a matter of decades (or faster if transapients were involved).

Sure. Weather machines would be able to substitute for an ozone layer very quickly. I'm not sure of the level of effort required to fix a mildly irradiated ecosystem.