The dog Laika, the first living creature to orbit the Earth, did not live nearly as long as Soviet officials led the world to believe.
The animal, launched on a one-way trip on board Sputnik 2 in November 1957, was said to have died painlessly in orbit about a week after blast-off.
Now, it has been revealed she died from overheating and panic just a few hours after the mission started.
The new evidence was presented at the recent World Space Congress in Houston, Texas, US, by Dimitri Malashenkov of the Institute for Biological Problems in Moscow.
Noted space historian Sven Grahn told BBC News Online that the new information was surprising and significant as it ended more than 40 years of speculation about Laika's fate.