These close-up images, taken by an electron microscope, reveal tiny one-cell organisms called halophiles and methanogens. In a two-year laboratory study, scientists subjected these organisms to increasingly lower temperatures to determine the coldest temperatures at which the microbes could survive and reproduce. The study shows the microbes could survive at below-freezing temperatures and are within the temperature range on present-day Mars. The organisms also developed a defense mechanism that protected them from cold temperatures. The halophiles and methanogens are part of a hardy group of microbes called extremophiles, which thrive in the harshest environments on Earth.