Moscow - A number of mice and eight gerbils sent into space in a Russian capsule destined to find out how well organisms can withstand extended flights perished during their journey, scientists said on Sunday as the month-long mission touched back down on earth.
Most of the 45 mice sent into orbit - along with the gerbils and 15 newts - died on the mission, which nevertheless returned with data that scientists hope will pave the way for a manned flight to Mars.
The animals on board the Bion-M craft died because of equipment failure or due to the stresses of space, scientists said.
The craft itself landed softly early on Sunday with the help of a special parachute system in the Orenburg region about 1 200km southeast of Moscow.
It was also carrying snails, a number of plants and microflora.
"This is the first time that animals have been put in space on their own for so long," Vladimir Sychov of the Russian Academy of Sciences announced upon the peculiar crew's return to earth.
But at the end of the experiment, "less than half of the mice made it - but that was to be expected", Sychov told Russian news agencies.
"Unfortunately, because of equipment failure, we lost all the gerbils."
The TsSKB-Progress space research centre's department head, Valery Abrashkin, said on the day the mission took off in April that the study was aimed at determining how bodies adapt to weightlessness "so that our organisms survive extended flights".
The capsule spun 575km above earth.
The space adventure has been widely praised by Russian state media as a unique experiment that no other country has yet pulled off.
Russia last sent mice into space in 2007 for a much shorter duration of 12 days.
France's Centre National d'Etudes Spatiales (CNES) space centre said 15 of the 45 mice came from a French research lab that is co-operating with the study.