The strength of dark matter might vary with the seasons...but why?

There's no reason at all why something as mysterious and cosmic should sync up with the changing of seasons on Earth...and yet now two independent sources claim that's exactly what it's doing. Just what is going on here?

Researchers with the DAMA experiment inside Italy's Gran Sasso Mountain have been claiming since 1998 that they have detected evidence of WIMPs, or weakly interacting massive particles, which are thought to be a leading candidate for dark matter. And the ebb and flow of the signal matches the seasons, which has led the DAMA researchers to suggest that this is because Earth's velocity varies relative to the surrounding dark matter as it travels around the Sun.

That may not seem like a lot to go on, but physicists have actually been able to use just that tiny hint to predict a possible cause: a WIMP that has a mass of between one and ten giga-electronvolts. The problem is that no other detectors have been able to find similar evidence for this signal, which has led to great tension in the dark matter hunting community.

But now the CoGeNT experiment, which completed 442 days of observation in a mine in Minnesota before a fire forced them out of their facilities, has become the second project to detect this dark matter signal. Even more excitingly, they've discovered evidence of the exact same seasonal variation that DAMA found, and in fact the evidence is strong enough to suggest that it's being caused by a WIMP of about seven giga-electronvolts.

This has led some researchers to declare this the smoking gun for dark matter, and it may help us understand why some detectors have found the WIMP signals and others haven't. UC Irvine theorist Jonathan Feng suggests the apparent discrepancy may just be an artifact of how the particles interact with the different elements in the detectors, arguing the different ratios of protons and neutrons could allow some detectors to see the WIMPs and others to miss them entirely.

Via New Scientist.