A Russian capsule filled with 45 mice and 15 newts has returned to Earth from a month-long mission in orbit with data scientists hope will pave the way for a manned flight to Mars.

According to the Associated Press, NASA scientists say the experiment is proposed to test the effects of weightlessness and other factors of space flight on cell structure.

Fewer than half of the 53 mice and other rodents who blasted off on April 19 from the Baikonur Cosmodrome survived the flight, Russian news agencies reported.

"This is the first time that animals have been put in space on their own for so long," said Vladimir Sychov of the Russian Academy of Sciences' institute of medical and biological research.

The capsule contained 45 mice and 15 newts as well as snails, gerbils, plants and microflora. It landed softly in the Orenburg Region, about 750 miles southeast of Moscow, according to the report. State television said that not all of the animals on the Bion-M craft had survived but provided no other details.

The mice and other animals were to be flown back to Moscow to undergo a series of tests at Sychov's institute, which is part of the Russian Academy of Sciences.