Air currents above cracks in Arctic ice are drawing mercury, a neurotoxin, into the snow and ice, say researchers.
The first measurement of radiation at Mars' surface has implications for a human mission to the Red Planet, as well as for where Mars' missions might find traces of Martian life – if it was ever there.
For US Army Capt. Tom Hickey and his platoon, saving Sadeel in 2007 was the best part of their tour in Iraq.
Readers write about parents' rights in abuse investigations, new flush toilets in India, and what it takes to go car-free.