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Humans face difficulties in space. The low or zero gravity changes how the blood flows and causes motion sickness, muscle loss and tiredness. Weightlessness can also cause bone loss. Scientists at the University of Delaware are testing little worms to better understand how space travel affects astronauts. The millimeter-long worm is called C. elegans. The see-through worm has no backbone and is often used in medical studies because it has a short life, and 70 percent of its DNA is the same as human DNA. Chandran Sabanayagam is a scientist with the university. He built a micro-gravity simulator, or machine, to test how the worms would perform in the actual zero gravity of space. Mr. Sabanayagam says the C. elegans turn around and around in the simulator for one week. Then, the scientists take out the worms and look for changes in their epigenome. The epigenome are chemical markers that tell the DNA in the cells how to perform. They can be changed by the environment. And those changes pass from one generation of worms to the next. Mr. Sabanayagam says identifying epigenomic markers is important for human studies in the future. He says he thinks scientists can find human genes like those in the worms that responded to microgravity. Chandran Sabanayagam expects C. elegans to visit the International Space Station within two years. He says he hopes the worm studies information can help develop tests to measure an astronaut’s health.