The five heroic sex geckos sent into space on July 19 to study sexual reproduction in zero gravity died before returning to Earth on Monday, Russian officials said.

It is unclear what they died of, or whether the intrepid geckos ever mated in space. Their tiny, partially mummified bodies were found within their enclosure aboard the small Foton-M4 spacecraft at the conclusion of their mission.

"All geckos, unfortunately, died," the Russian Space Agency said in a statement. "The date and conditions of their deaths will be determined by specialists."

See also: 12 facts about space that will rock your world

The geckos gained international recognition in late July when Russia said it had lost contact with the satellite, raising the possibility that the experiments would be a failure and the geckos would orbit the earth for months before their food supply ran out.

Communication was restored within a few days. But the satellite did change its orbital trajectory during that time, and it is unknown whether all of the life support systems remained functioning throughout the period.

The satellite carried four female lizards and one lucky male. Russian scientists hoped the mating rituals of the lizards and characteristics of their eggs would allow them to learn more about how the lack of gravity affects sexual reproduction in space.

The habitat for the Russian space geckos, seen before their launch in July.

“The lizards died about a week before landing,” a representative of the Russian Academy of Sciences' Institute of Biomedical Problems told the Russian news agency Itar-Tass. “It’s still too early to talk about the geckos’ cause of death,” the official added.

According to a report in Russia's Interfax wire, the space agency will likely appoint an emergency commission to determine the animals' cause of death.

The mission has, however, proved one kind of space sex can exist and thrive. The satellite was carrying other species, including fruit flies — which did successfully breed in space and survived the journey home.

In addition, mushrooms and seeds were also aboard, according to The Guardian.