Ever since I was a child, I’ve been fascinated by scientific discoveries. I remember reading a special article in our local newspaper about scientists searching for life on Mars. To my disappointment, they weren’t seeking little green men; instead, they were hunting for water. Nearly 30 years later, their search continues.
Why is water so important? The primary reason is that life, as we know it, relies on water. While not all lifeforms on Earth require oxygen or light, every single one needs water and plants may even “scream” when there is not enough.
However, is the pursuit of water in outer space simply following the only path we know? Are we ignoring the fact that we depend on water solely because we evolved on a planet covered with it? If life had evolved without water, it wouldn’t need water, right?
While this claim surfaces occasionally and appears logical at first, there’s more to water’s role as the cradle of life than mere coincidence. We can assume that the laws of physics and chemistry remain consistent across the universe, making them universal.
If this holds true, water is as important elsewhere in the cosmos as it is here on Earth. Here are four reasons why water is essential for life:
- Water is an excellent solvent. A wide range of molecules dissolve in water, breaking substances down to the molecular level. This process makes these molecules available for chemical reactions with other dissolved molecules. Life depends on these chemical reactions, with millions taking place in the human body alone. Chemical reactions require a solvent, and water is one of the best. Although other solvents, such as liquid ammonia or hydrogen sulfide (H2S), have been proposed, they might lack additional properties crucial for supporting life.
- Water molecules maintain the right amount of force. Neither too strong nor too weak, water molecules are slightly polar, meaning they have negative and positive ends. They are somewhat similar to magnets but far less powerful. As a result, water molecules briefly bond with each other before releasing and forming new bonds with nearby molecules. This characteristic gives water its fluidity, allowing it to flow without breaking apart or sticking together too much. Such cohesion is vital for transporting materials like oxygen, nutrients, and the building blocks of organisms within living beings.
- Water requires significant heat to warm up. Maintaining a stable temperature is crucial for life, and living in water (or being primarily composed of water) simplifies this task. In terms of physics, water has a high heat capacity, meaning it needs more energy to heat up and more energy to cool down compared to other substances. For instance, a metal object in the sun quickly becomes too hot to touch, while a glass of water in the sun is unlikely to become undrinkable. Water’s temperature is more stable than that of other liquids, such as methane or ammonia, which are also considered potential environments for life. For organisms composed of water, this means less effort is needed to maintain their body temperature. For Earth, it contributes to a more stable climate.
- Water becomes lighter when it freezes. Most substances become denser when they solidify, a result of the natural properties of materials—they contract when cooled. However, water is an exception. When it freezes, water becomes less dense and therefore lighter. The consequence is clear: ice floats. This is why lakes and oceans freeze from the top down, not the other way around. Beneath the North Pole lies a vast expanse of water teeming with life, which would not be possible if ice sank. Without floating ice, life would not only struggle to survive, but it might never have arisen in the first place.
Besides these points, water has other properties essential for life. However, many of them may be crucial only for life as we know it. The properties listed above are the most fundamental aspects that make water the ideal substance for life, regardless of where in the universe it evolves.
While other liquids, such as liquid ammonia or the methanol lakes on Saturn’s moon Titan, are also on the radar of extraterrestrial life-seekers, water remains their best bet.