Final answer:
The most significant factors for supporting life on a Solar System body are water, moderate temperatures, and sunlight.
Step-by-step explanation:
The three factors that would be most important for a body in the Solar System outside of Earth to support life are water, moderate temperatures, and sunlight. These are essential because water is necessary for all known forms of life, moderate temperatures facilitate the presence of liquid water and stable environments suitable for life, and sunlight provides the energy needed for photosynthesis, which drives food chains and ecosystems.
Earth's position in the habitable zone, the presence of a robust biosphere, and its atmospheric composition allow for liquid water and moderate temperatures. However, the possibility of life existing in subsurface oceans of icy moons or beneath the surface of Mars, where different conditions may prevail, is also being considered in astrobiology.