MOSCOW, September 03./ITAR-TASS/. As the death of geckos aboard the Russian Photon satellite remains a mystery, the investigation is underway, but there are still more questions than answers, experts said on Wednesday.

The autopsy proved that the geckos had died from a sudden pressure rise aboard the satellite a day or two before its re-entry capsule landed on Monday, Sergei Savelyev, a researcher at the Institute of Human Morphology, who is in charge of the experiment, told ITAR-TASS.

“It appears there was an abrupt pressure surge. This is borne out by pathological changes in the internal organs - the heart, the lungs, the liver and others. The changes occurred very fast: the lungs were contracted, with stagnant blood found in their vessels. Moreover, the blood from all internal organs and systems rushed to the heart, filling large vessels and the atrial cavity,” he said.

The expert said pathological changes in the internal organs were identical in all geckos.

Another fact corroborating the pressure surge theory is that all reptiles died practically at the same time.

Savelyev said the sharp rise in pressure might have been caused by a malfunction of the satellite’s life-support system.

However, experts at the Institute of Medical and Biological Problems said that the geckos had died from indigestion caused by low temperature and the resulting metabolic slowdown.

But Savelyev dismissed this theory as unfeasible. “The autopsy showed that they were not eating at all. No traces of food were found [in their bowels]. They felt cold and did not eat,” he said.

He also said that starvation and low temperature could not have killed all the reptiles at the same time.

“I can think of no other explanation but a pressure surge,” he said.

However, Vladimir Sychev, Deputy Director of the Institute of Medical and Biological Problems, told ITAR-TASS that there was no change of pressure.

“I have the autopsy data too but there are no grounds to interpret them as a pressure surge. In fact, it simply could not have occurred. There were [fruit]] flies there and had this been true, they would have died too. But they didn’t,” he said. Sychev said the geckos’ death remained an answered question and experts would continue their investigation.

The Federal Space Agency (Roscosmos) said it would set up a special commission to investigate the incident.

“Hypothermia is not the main possible cause but only one of the options. Others include a possible malfunction of the onboard equipment and life-support system,” the source in the space industry told ITAR-TASS.

Roscosmos said that the fruit flies “got through the flight quite well, grew and bred” but “all geckos died, unfortunately”.

The Photon-M4 satellite was launched on July 19, 2014 from the Baikonur space centre in Kazakhstan. The spacecraft carried specimens for research of the biological effects of zero gravity and cosmic radiation.

The specimens include geckos, silkworm eggs, dried seeds, fruit flies, and mushrooms. The geckos were part of biology experiments conducted by Russia’s Institute of Medico-Biological Problems on the effects of weightlessness on mating.

Another experiment aboard the spacecraft is designed to measure the effects of microgravity on semiconductor crystal growth.

Several hours after the blastoff, the control communication with Photon-M was disrupted, although the spacecraft continued to transmit telemetric information. As a result of the malfunction, the satellite stayed on the support orbit, instead of being placed into the target orbit by its own engine on command from the Earth. The Institute of Medico-Biological Problems said after the control loss incident that it did not affect in any way the onboard life support system and the programme of automatic experiments.

It took seven days to restore communication with the spacecraft, space experts said.

The spacecraft’s flight time was limited to 60 days.

Photon satellites are designed and made by the Progress Rocket and Space Centre for research and experiments in such fields as the physics of weightlessness, space biology and biotechnology, including the affect of outer space on living specimens.

The first satellites of the series was launched in 1985 and operated for 13 days.

In 2005, the Photon-M2 satellite carried out about 20 scientific Russian and European research programmes. The next satellite, Photon-M3, in 2007 performed 45 Russian and foreign experiments.