In 2008, a suitcase-sized experiment dubbed Expose-E subjected organic compounds and living organisms such as lichen, seeds and algae to the hostile environment of outer space.
The result? You can freeze it, thaw it, vacuum-dry it and expose it to radiation, but life survives, scientists said.
Life on Earth is protected by our atmosphere from harmful ultraviolet rays, but the space samples endured the full power of the sun's rays.
The samples were returned to Earth in 2009 and the results of the study have been published in the journal Astrobiology.
Lichen have proven to be especially tough, researchers said, and, some species have continued to grow normally since their return to Earth.
"We are exploring the limits of life," ESA's Rene Demets said in a release from the agency's Paris headquarters.
Living organisms persevering in open space supports the idea of "panspermia" -- that life can spread from one planet to another or even between solar systems, researchers said.