Russians recovered a furry crew that spent a month in microgravity this week, only to confirm most arrived back on earth dead. Sad, but not as bad as it sounds:

Arstechnica — A Russian spacecraft containing 45 mice, 8 gerbils, and 15 newts returned to Earth on Sunday. The spacecraft, a modified Bion-M life sciences satellite, was launched in April 2013 and was intended to study the biological effects of long-term weightlessness. However, due to a combination of equipment failure and what scientists referred to as “the stresses of space,” fewer than half the mice (and none of the gerbils) remained alive after their month in space. The newts were fine, though.

That most organisms, including humans, undergo physical changes in prolonged microgravity is already well-understood; the United States and the Soviet Union (and later Russia) have been conducting long-duration manned space flights as far back as the early 1960s, and there is a plethora of data on the subject. However, conducting detailed experiments on the biological deficits incurred through long exposure to microgravity—including skeletal and muscular deterioration—is ethically difficult because at least some amount of the damage could be irreversible.