Let’s learn about life forms that have survived in space

astronaut: Someone trained to travel into space for research and exploration.

bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

casing: (n.) Some structure that encloses the potentially fragile working parts of a device, such as a cellular phone. It affords those internal parts protection by fully covering, or encasing, them. (in food science) The outer skin or material used to hold — or encase — the meat and other ingredients used to make a sausage.

cosmos: (adj. cosmic) A term that refers to the universe and everything within it.

dormant: Inactive to the point where normal body functions are suspended or slowed down.

germ: Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

International Space Station: An artificial satellite that orbits Earth. Run by the United States and Russia, this station provides a research laboratory from which scientists can conduct experiments in biology, physics and astronomy — and make observations of Earth.

lichen: A blend of a fungus and an alga. Neither of these organisms is a plant; the lichen isn’t a plant either. Slow-growing, lichens organisms live on the surface of rocks, trees or wood over many years. Lichens are a component of the soil crusts or “desert crusts” that cover the soil in some deserts .

Mars: The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

moon: The natural satellite of any planet.

moss: A small, flowerless green plant that lacks true roots. It tends to grow as carpets or rounded cushions in damp habitats. It can reproduce asexually, through fragmentation, or by means of spores released from stalked capsules.

organism: Any living thing, from elephants and plants to bacteria and other types of single-celled life.

oxygen: A gas that makes up about 21 percent of Earth’s atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

panspermia: A theory that life on Earth evolved from microbes or from chemical building blocks of simple life that rained down onto the planet from outer space.

planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.

radiation: (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

risk: The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

species: A group of similar organisms capable of producing offspring that can survive and reproduce.

spore: A tiny, typically single-celled body that is formed by certain bacteria in response to bad conditions. Or it can be the single-celled reproductive stage of a fungus (functioning much like a seed) that is released and spread by wind or water. Most are protected against drying out or heat and can remain viable for long periods, until conditions are right for their growth.

stratosphere: The second layer of the Earth’s atmosphere, just above the troposphere, or ground layer. The stratosphere stretches from roughly 14 to 64 kilometers (9 to about 31 miles) above sea level.

tardigrade: An eight-legged creature not much larger than the period at the end of a sentence. Tardigrades live in many places, including ponds, the sea floor and parts of Antarctica where rock sticks above the ice.

tobacco: A plant cultivated for its leaves, which many people burn in cigars, cigarettes, and pipes. Tobacco leaves also are sometimes chewed. The main active drug in tobacco leaves is nicotine, a powerful stimulant (and poison).

universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

void: An empty space or cavity.