ANAHEIM, Calif. -- For the first time in history, humans are making serious plans to carry life to other worlds, but experts said Monday it's uncertain whether plants and animals from Earth can thrive and evolve on other planets.
"For a long-term habitation of Mars, you'll have to grow crops, deal with microbes and so forth," said David Morrison of NASA's Ames Research Center. "We have to understand the response of those organisms to the different conditions."
Organisms that evolved in the gravity of Earth may not thrive in the lighter gravity of the moon or Mars, said NASA's Emily R. Morey-Holton. In the one-sixth gravity of the moon and the one-third gravity of Mars, fundamental processes of heat convection and sedimentation change. Also, the surface tension of water, which shatters easily in Earth's gravity, becomes a strong barrier in lighter gravity and could affect basic biological functions.
"We don't know the effect of these changes," said Morey-Holton. "We have to learn if Earth organisms can live and evolve in these changed conditions."
For instance, Morey-Holton said, researchers found that tadpoles hatched in orbit never developed lungs. In the low gravity, the surface tension on air bubbles became so strong that the tadpoles could not punch through to breath, she said. "They would hit the bubbles and just bounce off."
In another orbital experiment, a type of mustard plant failed to thrive in space because water droplets clustered about the roots, blocking absorption of nutrients. Again, the cause is thought to be the enhanced surface tension of the water droplets.
Changes in gravity could also affect how genes work and could even affect evolution, said Morey-Holton.
"Some researchers are looking for gravity-dependent genes," she said. "There is concern that in a different gravity some genes may fail to turn on while others could shut down."
Such actions could dramatically alter a plant or animal or even cause lethal changes, she said.
In one orbital experiment, several generations of human kidney cells were cultured and researchers have found that the genes in the space grown cells changed. Just how the changes would affect the cells is not known.
"If we find gravity-sensitive genes, there is no reason why we can't have designer organisms that would be viable in the new environment," said Morey-Holton. In effect, Earth plants or animals could be genetically altered so they would thrive in the changed conditions of Mars and would then be put on board a space-age ark that would carry colonists to the Red Planet.
NASA is planning a series of experiments on the International Space Station to find Earth organisms best suited for Mars. Plants and animals will be grown through several generations and then analyzed for genetic changes, said Morrison.
The NASA officials spoke during a meeting of the American Association for the Advancement of Science.