If the odds of getting fried by a GRB in a given year is 1 in 14 million … then on average we should be getting fried every 14 million years … I don’t think the geologic record supports this.
I take it that this upcoming event is not the sort of thing that will cause The End of the World As We Know It?
Not “in a given year”; over a human lifetime. The paucity of data makes it impossible to make a credible estimate of probability, but we can observe that thr frequency with which GRBs have a catastrophic effect upon the Earth is no less than on the order of hundreds of millions of years. This may, however, give some partial answer to the supposed Fermi paradox; although we observe them infrequently today (and in our astronmically short period of observation, from extragalactic sources) they could have been far more frequent in the early evolution of our galaxy and would be most commonly encountered closer to the galactic core, scouring potential homes of early extraterrestrial life (along wih all of the other radiation and hazards) making the bulk of the galaxy uninhabitable during our early evolution. We may just be at a comfortable medium that is the perfect haven for (our form of) life. Or perhaps there are galactic entities of tenuous plasma cells seeking out supernova and gamma ray bursts the same way a bear in Yosemite looks for an unattented cooler of hot dogs; sort of a cosmic Yogi the Bear searching for pic-a-nic stars.
Stranger
Even at hundreds of millions of years, we’ll have near certainty it occurred at least once. But point taken.
Fermi’s Paradox can be applied locally, any life destroying GRB within 100 light years would have destroyed us as well. From the OP, only half a planet would have life destroyed, the other half will still provide the means to completely recolonize. Nah, a better answer to Fermi’s Paradox right now is we just don’t have the technology. Sure we’re finding exoplanets, but we basically can only determine the mass and orbit … getting the emission spectrum of their atmosphere may be a few years off still. Just two green lines is all we ask …
They’re typically the result of creation of black holes, and are the most energetic things observed in the universe. Gamma ray bursts emit more energy in a period of a few seconds than our sun emits during its entire 10 BILLION year lifespan.
Now considering that they are associated with black holes, they’re directional- firing the energy along the axis of rotation. So if the axis of rotation isn’t aimed in your direction, you’re ok. OTOH, if it’s aimed at you, you can be thousands of light years away and you’re still toast. The example I mentioned above (Eta Carinae) is 7500 light years from earth, which is a fairly long way in astronomical terms.
No GRB are directional (like laser beams) unlike supernovae. If they’re not pointed at you, you’re OK. So life on Alpha Centauri planets could have been destroyed by a GRB that left us unscathed. — (maybe. I’m not sure of the angular spread of a GRB and how near the sun is to a line from such a hypothetical to Alpha Centauri.)
But it’s certainly possible we could be spared by a GRB that wiped out life within a 100 or us.
As lalaith noted, a GRB has been hypothesized to have contributed to an extinction event (the Ordovician extinction, about 445 Mya) there is no direct evidence for this (too far in the past to used [SUP]14[/SUP]C dating). A GRB consists purely of gamma rays (very high energy electromagnetic radiation) emitted in what appears to be a tightly collimated beam. We’ve never observed one to occur close enough to be able to identify the source, and in fact all GRBs observed to date have an extragalatic origin. The width of a possible field at those distances may still be quite small, perhaps only a few parsecs across, so it would be entirely possible for a GRB oriented orthogonal to the plane of the galaxy to go through without affecting any system.
Although a GRB will only last for a few seconds and directly affect the facing side of a planet, the impact upon the planetary atmosphere may be dramatic. For us, a strong GRB would both strip away the ozone layer and ionize the stratosphere and upper troposphere, drastically changing the climate for hundreds of thousands or millions of years, and probably disrupting the ‘normal’ regulatory mechanisms for even longer. Would it happen to Earth today, we could certainly expect the collapse of civilization and likely extinction of all land-based vertebrates including humanity. (Never mind fantasies of “waiting it out in underground bunkers”; with thousands of generations before the climate may even be possible of sustaining agriculture and unprotected surface activity, the survivors might as well just be living in Antarctica.)
The reason I suggest that it may be applicable as a response to the supposed Fermi paradox is that some of the hypothesized progenitors such as the collapse of blue supergiant stars and interaction of neutron stars or collapsars would have been much more common early in the evolution of our galaxy and are still more densely found toward the galactic core. Many GRB progenitors are located far away (by the measurement of their redshift) and come from very early (the first few billion years); assuming a high frequency and density toward the core that may put some bounds on the estimate of when any kind of chemical life we could conceive would likely be able to survive long enough to develop intelligence, though obviously such a model would be making a lot of assumption about survivable conditions and the time necessary for advanced life to evolve.
Note that while GRBs are the most energetic events we see in astronomy they are not the only source of extraterrestrial hazardous radiation. Bursts of energetic heavy cosmic rays (highly energetic protons and heavier nucleons, as well as very energetic electrons) are also often seen and hypothesized to occur with greater density toward the galactic core, again being sourced from supernovae and other large mass ejections. Unlike the purely ionizing radiation of GRBs, heavy cosmic rays can transmute other elements creating radioactive isotopes that may persist long after the initial interaction. Although we haven’t seen mass bursts of heavy cosmic rays on par with the energy in GRBs, we’ve observed individual particles, or rather their interactions with the upper atmosphere, that have a momentum equivalent to a thrown baseball. Given that we’re talking about a particle with the mass of a single nucleus compared to a baseball (containing on the order of 100 billion nuclei, plus attendant electrons) that would be a pretty impressive throw that even Roger Clemens would have to bow down to. A large mass of similarly energetic cosmic rays striking the atmosphere in short order could create a lethal shower of secondary particles and could affect both the climate and composition of the atmosphere.
Then there are superdense interstellar clouds which could impact the solar system at high rates of speed (~100 km/s) compressing the heliosphere or disrupting the heliopause, potentially creating powerful magnetic storms or allowing in a much greater flux of energetic cosmic radiation. Or a runaway hypernova chain in the center of the galaxy, spewing out lethal radiation at >0.99 c. Or giant space goats…well, okay, that’s pretty unlikely, but you get the idea. The Earth isn’t some special place that the universe has decided to protect and foster; it just has happened to be far enough away from everything else that life (our form of life, at least) has managed to gain a toehold and evolve past just sexual reproduction and swimming around in the oceans. (Not that there is anything wrong with that; hey, some of my best friends are…never mind.) But there is no guarantee that this all won’t be wiped out tomorrow by some event that not only could we not prevent or protect ourselves from, but we might not even see or have any means of forenotice.
Sweet dreams…
Stranger
What kind of residue should we expect to find? Would a GRB disassociate some of the rocks. AFAIK the iridium layer for the K-T boundary is fairly obvious and I can’t imagine it took very long to lay that down. Granted, iridium is pretty easy to spot but it seems to me any “unnatural” silicon compounds would be easy to spot as well, 445 Mya isn’t an especially long time.
Well, if there were any direct effects on the surface, we would expect to find an asymmetric effect, where only half the surface showed damage from the event.
Considering how much the planet changes over time, and how little evidence there would be, it might have already been found, but nobody has realized it.
Something like the late Pleistocene extinction event in the Americas, but not in the old world? It’s somewhat controversial that neolithic man of the Clovis Culture had the ability to hunt down every last horse in North America and eat them, especially since the Clovis Culture disappear at around the same time.
My understanding of the GRBs we’re seeing now all came from a very long ways away, thus a very long time ago. Is it possible the nature of the universe has changed in ways that make GBRs not longer possible?
You’d expect a GRB to kill a lot more than the megafauna. From the right range, it’d kill virtually everything - right down to the soil microbes. But, yeah, that would be the kind of thing you’d look at.
The issue for very ancient extinctions is that we might only have fossils in one or two parts of the planet dating back to that extinction event. To prove a GRB caused the extinction by looking at asymmetry, you’d need one good fossil bed from at least three hemispheres. Even then, you’d get a lot of confusing information: some species would go extinct globally from the resulting after-effects, and some species killed locally would be able to repopulate from survivors on the other side of the planet. So the evidence to suggest a GRB extinction event would require some pretty thorough analysis of many different species. Not impossible, but there won’t be any Eureka! moment from a single find.
I’m still not losing any sleep over it.
Nor should you, really. There is absolutely nothing we could do to protect the Earth or its inhabitants from it. On the other hand, asteroid impact is a hazard that we could mitigate using fairly modest development of largely existing technology, and for a cost not much more than the annual budget of NASA.
Stranger
Interesting discussion and info. Remedial question here: if a GRB was aimed at us, but the sun was in the way when it got to our vicinity, would we still be affected? What about if the moon was in the way? Would there be a spot on the earth where life is intact, surrounded by a hemisphere of death? (sounds like a good sci-fi story). How about if another planet was in the way? Does it need to be a clear shot from it’s source?
Also, I assume when we are talking about one hemisphere being impacted and the other not, it may not be neat and clean (eastern/western or northern/southern), but if it came obliquely, I wonder how that may adjust the impact. For example, if it hit squarely the southern hemisphere, which is mostly water, would our chances be improved, since most of humanity and it’s infrastructure resides in the north?
I am not sure I saw a response to Senegoid’s question about inanimate objects. If it’s curtains for all living things in one hemisphere, would our cities, structures, and machines be left intact?
For the most part, yes. Gamma radiation doesn’t disrupt a whole lot of the physical structure of an animal, but damage to DNA can kill a whole cell, and it doesn’t take very many dead cells to kill the whole animal. If a piece of steel has 1% of its atoms disrupted, it may be weakened, but it won’t curl up and die.
Of course, things like cities won’t last long without someone to maintain them.
Since about 3 meters of concrete will block all gamma, people inside multi-story buildings, or underground parking garages would not even be effected by a gamma ray burst. At least directly.
When you have to leave the protected area, things are going to look quite grim
I thought this was going to be about The Effect of Gamma Rays on Man-in-the-Moon Marigolds. How you persevere even after the world goes insane and murders your pet rabbit. Nevermind, carry on… 
Any planet-sized object is going to be a perfectly effective shield. The Sun or any gas giant could shield the entire Earth. The Moon or any other planet would leave a shadow.
And a burst coming from directly along either the North or South pole would be the best-case scenario. Air doesn’t readily cross the Equator, so a direct all-north or all-south shot would minimize the atmospheric effects in the other hemisphere.
Someone else in this very thread said it would penetrate a half mile underground?
Well that’s crazy talk.