Whereas Earth has only one satellite (aka. the Moon), Mars has two small moons: Phobos and Deimos. And whereas the vast majority of moons in our Solar System are large enough to become round spheres similar to our own Moon, Phobos and Deimos are asteroid-sized and misshapen in appearance.
Microorganisms, like certain bacteria and yeasts, living on the human skin or in the nose, mouth, throat, small and large intestine and vagina, are part of the normal human flora; they prevent overgrowth of harmful microorganisms. Some of these microbes, when overgrow, may become pathogenic, though.
A microorganism or microbe is a microscopic living organism, which may be single-celled or multicellular. The study of microorganisms is called microbiology, a subject that began with the discovery of microorganisms in 1674 by Antonie van Leeuwenhoek, using a microscope of his own design. Microorganisms are very diverse and include all bacteria, archaea and most protozoa. This group also contains some species of fungi, algae, and certain microscopic animals, such as rotifers. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses (and viroids) as microorganisms, but others consider these as nonliving.