Signs of Dark Matter From Minnesota Mine 158
thomst writes "Juan Collar, team leader of COGENT, an experimental effort to detect WIMPs (Weakly Interacting Massive Particles), recently presented a paper detailing 15 months of data collected via a pure germanium detector located deep in a Minnesota mine which seems to confirm similar results reported by a European effort called DAMA/LIBRA. The results are particularly intriguing, because they appear to show a seasonal variation in the density of WIMPs that accords with models which predict Earth should encounter more WIMPs in Summer (when its path around the Sun moves in the same direction as the Milky Way revolves) than in Winter (when it goes the opposite direction). The most interesting thing about the COGENT experiment is that the mass of the WIMP candidates it records is significantly less than most particle physicists had predicted, according to popular models. (Ron Cowen wrote an earlier article about COGENT last year that goes into a lot more detail about how COGENT works, what its team expects it to find, and why.)"
Re:that always bothered me (Score:5, Informative)
Note that the solar system co-rotates with the Milky Way matter around it, so the 225-250 Myr period with respect to an inertial frame is not relevant for dramatic effects. The sometimes discussed effect linked with massive extinction is the periodic crossing of the Milky Way plane, which occurs about every 35 Myr. The last great extinction ocurred 65 Myr ago, so one should have seen at least one or two of these plane crossing.
Another possibility is the solar system crossing spiral arms, with period of order of 150 Myr, but this is debated.