Moons of outer planets may provide a home for life because a. some have liquid water. b. some have organic molecules. c. some have an interior source of energy. d. all of the above

Liquid water is a fundamental requirement for life as we know it. It's the solvent in which biochemical reactions occur, supporting processes essential for the existence of living organisms. Many of the moons of outer planets, such as Europa (a moon of Jupiter) and Enceladus (a moon of Saturn), are believed to have subsurface oceans of liquid water beneath their icy crusts. The presence of liquid water suggests that these moons could potentially harbor life. Scientists look for signs of water plumes or geysers, which may provide additional evidence of the liquid water underneath the surface. This exploration increases our understanding of what makes a celestial body habitable and the possibility of finding life beyond Earth.

Organic molecules are critical because they form the building blocks of life, including proteins, nucleic acids, and carbohydrates. These molecules contain carbon and are involved in various biological processes. Several moons of the outer planets have been found to contain these molecules. For instance, the Cassini spacecraft detected complex organic molecules in the plumes ejected from Enceladus. This discovery indicates that the moon possesses the chemical ingredients necessary for life. The study of these organic compounds helps scientists determine the potential for life and understand the prebiotic chemistry that could lead to the formation of living organisms.

An internal energy source is essential for maintaining liquid water and driving biochemical reactions necessary for life. These energy sources can be in the form of volcanic activity, hydrothermal vents, or tidal heating. For example, the intense gravitational interactions between Jupiter and its moon Europa generate tidal forces that cause internal friction, creating heat within Europa's interior. This process keeps the subsurface oceans from freezing and provides a constant energy supply that could support microbial life. Internal energy sources are thus crucial for sustaining habitable environments on moons far from the Sun, where surface temperatures are extremely low. Understanding these processes is key to assessing the potential for life in such extreme environments.