3000km^2 in Argentina: the Pierre Auger Observatory (http://auger.org http://auger.org) for ultra high energy cosmic rays. It was meant to get a follow-up 7x t

3000km^2 in Argentina: the Pierre Auger Observatory (http://auger.org http://auger.org) for ultra high energy cosmic rays. It was meant to get a follow-up 7x the size in Colorado but it was defunded by NSF as a result of the 2008 crisis. The exciting prospect of this was that at extremely high energies of cosmic rays (where they get very sparse: 1/km^2/century), these charged particles have a relatively short range (in astronomical terms - they're not from our galaxy; look up the GZK effect). That meant that they wouldn't be deflected by magnetic fields as much and could - thus the intent - be traced back to their sources. The clou: we have no credible theory for any process that would put this much energy into a single particle, so knowing their sources would be a step towards solving a physics mystery. Source: worked on my PhD there.