Dark matter was discovered 80 years ago when astronomer Fritz Zwicky spied a galaxy cluster whirling so fast, the galaxies were bound to fly apart unless something — something less luminous than ordinary stars or gas — held them together.

Decades later, the scientific community concedes the existence of dark matter, after many different kinds of experiments and simulations, but physicists still don't know what it is.

But confidence is growing. The last 15 years have seen the construction of several exotic detectors buried deep underground, and those detectors may be giving us our first view of what dark matter is made of. In January's cover story, Dan Hooper discusses these experiments, their results, and their most recent find: a seasonal variation in detections that indicate Earth might be moving through a WIMP wind as it orbits the Sun.

We summarize the underground experiments below. All of these experiments are continually increasing their detector mass, so the masses listed here are not fixed.

Guide to Dark Matter Experiments
Experiment Location Detector Start Date Results
Gran Sasso, Italy 250 kg sodium iodide crystals 1998 Thousands of events with annual variations
Soudan, Minnesota CDMS-II:
4.5 kg germanium crystals
9 kg germanium crystals
2003 No claimed WIMP detections yet
CoGeNT Soudan, Minnesota 500 g germanium crystal 2004 Hundreds of events with possible annual variations
CRESST Gran Sasso, Italy 2.4 kg calcium-tungstate crystals 2006 Tens of events, possible WIMP signal
XENON-100 Gran Sasso, Italy 161 kg liquid xenon 2009 No claimed WIMP detections yet
LUX Homestake, South Dakota 350 kg liquid xenon 2011 No science results yet
XMASS Kamioka, Japan 800 kg liquid xenon 2011 No science results yet


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