The temperature of a planet critically affects its ability to support life by determining whether liquid water, essential for all known life forms, can exist. Life on Earth thrives within a temperature range roughly from -15°C to 122°C, beyond which biological molecules such as proteins and nucleic acids degrade or water becomes unavailable in liquid form. Too low temperatures freeze water, preventing necessary chemical reactions, while too high temperatures can denature biological molecules and evaporate water—both making life unsustainable. Hence, a planet’s temperature must usually fall within this "habitable" range to support life, as it influences cellular processes, biochemical reactions, and overall biological activity.
Temperature and Liquid Water
One of the fundamental reasons temperature influences habitability is its control over the state of water. Life requires liquid water for biochemical reactions and nutrient transport. If a planet is too cold, water freezes, limiting available liquid water. If too hot, water evaporates quickly, also reducing liquid water availability, which severely restricts life support potential.
Biological Limits
Microorganisms on Earth demonstrate that life can persist under extreme conditions, but there are limits. Some microbes can survive at temperatures as low as -15°C by using antifreeze-like intracellular solutes and thin films of liquid water in ice. At the high end, certain archaea can survive up to 122°C, often under high pressure that stabilizes liquid water. Biological membranes and proteins, however, degrade beyond these thermal limits, setting upper and lower bounds for life.
Planetary Habitability
A planet’s average temperature is influenced by its position in the habitable zone ("Goldilocks zone") around its star, atmospheric composition, and greenhouse effects. Earth’s ability to maintain an average surface temperature around 15°C allows a stable environment for life. Variations outside this range on planets like Venus (too hot) and Mars (too cold) demonstrate why temperature is a key determinant in whether life can exist.
Other Influences
Temperature fluctuations and seasonal variations also affect planetary habitability by influencing climate stability and ecological dynamism. Extreme seasons or temperature swings, while not necessarily prohibitive, can challenge the maintenance of stable biospheres.
In summary, temperature affects a planet's ability to support life mainly by governing the presence of liquid water and by setting biochemical limits on life forms. A planet needs to maintain a temperature range that keeps water liquid and biological molecules stable to be considered habitable. This range is typically believed to be between about -15°C to 115°C for Earth-like life. Outside these limits, the chances for life as we know it diminish drastically.
