Five geckos sent into orbit to test the effect of weightlessness on the small lizards' sex lives have all died, the Russian space agency said on Monday.
The Foton-M4 satellite on which the geckos spent the past month and a half returned to earth as planned on Monday and the various species travelling aboard were removed.
"Unfortunately all the geckos died," said the Roskosmos space agency in a brief statement.
Interfax news agency later quoted an expert that worked on the mission as saying "that according to preliminary data it is becoming clear that the geckos froze" after their heating system failed.
The fruit flies that were also travelling on the satellite, however, survived and had reproduced, Roskosmos said.
Roskosmos briefly lost control over the satellite following its launch, but was eventually able to restore contact and put the satellite in the proper orbit.