Death from the stars

Nothing too melodramatic today.

Observations of the 560m asteroid 1999 RQ36 have enabled some determination of its likely future movements. Feeding in 290 visual and 13 radar observations, researchers determined there was a one in a thousand chance of the asteroid striking the Earth in 2182, 172 years from now. As time passes, more observations will determine the asteroid’s path to a greater degree of accuracy, ruling an impact further in or out of contention, but for now that is a one in a thousand chance of a 10km wide, 500m deep crater opening up somewhere in the world or a large movement of water if it hits the ocean. Aside from a few headlines in the papers, the asteroid has acquired its own thread on the forums of the Sky at Night magazine.

Another danger that got a bit of airing recently is the danger posed by gamma ray bursts going off relatively nearby. GRBs are distant, intense flashes of gamma rays. They come in two types, long and short, believed to be due to supernovae of massive stars and the merger of binary neutron stars, respectively. The exact mechanism for generating the gamma rays is not known, but what is known is they happen and they are powerful. Researchers have modelled the effect of a GRB within around 6,000 light years from Earth. The result would be a stream of gamma rays so powerful that the ionisation of the atmosphere would cause a flash of light strong enough to blind anyone unlucky enough to witness it. The oceans would see plankton damaged severely down to around 85 metres depth, the damage being severe enough to shut down photosynthesis by organisms at these depths or shallower, for the ten seconds or so of the flash. The good news is after that burst, everything starts to go back to normal pretty quickly. There’d be a lot of nitrous oxide and other things we see from ionisation events in the atmosphere, plenty of radio disruption for a while, a need for regeneration of part of the ozone layer, which would also let in plenty of damaging radiation, but recombination chemistry and diffusion would start to fill in the hole as soon as the GRB shut off. Which is more encouraging. That and the fact that it is estimated the likelihood of a GRB going off within 6,000 light years is so low, only one would be expected over a length of time equivalent to the age of the universe.

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