Infinite sadness.

Five gecko lizards sent into orbit on a Russian space satellite as part of a sex experiment have all died, the Russian space agency says.

The Foton-M4 satellite returned to Earth on Monday, the Roscosmos agency said in a statement (in Russian).

Experts say the geckos may have frozen to death after the heating system broke down, Russian news agencies report.

They were sent into space as part of a study into the effect of weightlessness on their sex lives and development.

“We can say with confidence that they died at least a week before the landing because their bodies were partly mummified,” an official from Russia’s Institute of Medical and Biological Problems told Itar-Tass news agency.

BBC: Sex geckos die in orbit on Russian space project