Humans are well-equipped for life on Earth. But in space, it is a different story. Low or zero gravity changes how the blood flows and causes motion sickness, muscle loss and tiredness. Weightlessness can also cause bone loss. But scientists at the University of Delaware are experimenting with little worms to better understand how space travel affects astronauts.

The millimeter-long worm is called C. elegans. The see-through invertebrate is often used in medical studies because its life is only about two weeks long. Seventy percent of its DNA is the same as human DNA.

Chandran Sabanayagam is a scientist with the University of Delaware. He built a micro-gravity simulator to test how C. elegans would perform in the actual zero gravity of space.

"Imagine, if you have a container of water and you put an object in it, and it begins to settle to the bottom. But, before it hits the bottom, you flip the container upside down. And now it has to fall back down to the bottom. Before it reaches it, you flip it again. Essentially this instrument rotates and the object never hits the bottom. So essentially it's in freefall, similar to a satellite orbiting the earth."

Scientists use a computer to watch the worms as they turn. The computer shows the worms as they would look under a microscope. Mr. Sabanayagam says the worms turn around and around in the simulator for about one week.

After about a week the scientists take out the worms. They look for changes in the worms' epigenome. The epigenome are chemical markers that tell the DNA in the cells how to perform. The epigenome can be changed by the environment. And those changes pass from one generation of worms to the next.

Mr. Sabanayagam studies the epigenome as it relates to microgravity.

"When the worms are in a liquid environment some epigenomic marks persist (remain) even when we take the animal out of the liquid environment and put it back into normal ground conditions. So its offspring retains this epigenomic memory of the parents' liquid environment or microgravity environment."

The information the scientists have gathered suggests that the epigenomic marks appear during the early part of a worm's life. Mr. Sabanayagam says identifying epigenomic marks is important for human studies in the future.

He says he thinks scientists can find genes in the human genome similar to those in the worms that responded to microgravity. He says scientists could possibly observe those genes closely when astronauts travel in space.

Chandran Sabanayagam expects C. elegans to visit the International Space Station within two years. He says he hopes information gathered from the worm studies can be used to develop simple, low-cost and quick tests to measure an astronaut's health.

I'm Jonathan Evans.

Rosanne Skirble reported this story from Washington. Jonathan Evans adapted it for Learning English. Caty Weaver edited it.

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invertebrate – n. a type of animal that does not have a backbone

DNA – n. a substance that carries genetic information in the cells of plants and animals; an abbreviation of deoxyribonucleic acid

rotate – v. to move or turn in a circle

simulator – n. a machine that is used to show what something looks or feels like and is usually used to study something or to train people