About 71% of the Earth is covered in it. Roughly 60% of your body is made up of it. Every single living organism on Earth, from tiny bacteria to giant blue whales, needs it to survive. What is this substance that is so prevalent and necessary for life on Earth? If you guessed water, you’d be correct. Even organisms found in the most extreme environments, including 120 ˙F deserts and 36,000 feet deep in the oceans, require water to live. As a result, in their search for life beyond Earth, NASA has adopted the motto, “follow the water.” What is it about water that is so special for supporting life?
While H2O exists in all three states (solid, liquid and gas), the word ‘water’ refers to its liquid state. Liquids have unique characteristics that allow them to support life. For example, many liquids can dissolve chemicals, minerals and nutrients. Think about all of the substances you can mix in water. Salt, Kool-Aid, chocolate powder—the list is endless. Also, liquids can flow and spread. When you dump ice cubes onto a table, they barely cover the surface. However, when you pour a glass of water on the table, the water spreads out and the whole table gets covered.
Since liquids spread, they easily transfer the dissolved substances from one location to another. This is especially helpful for an organism that needs to transport substances necessary for life, like sugar and salt. These substances dissolve in water, which organisms can then transfer in and out of cells. This has led scientists to believe that if we find evidence of liquids on other planets, specifically water, we’ll be more likely to find life there as well.
The Search For Water
Scientists have scoured our solar system for evidence of liquids in an attempt to find signs of life. One place scientists have studied the most is the planet Mars. On Mars, observations of the surface show channels carved into the rock, which suggest a liquid once flowed there. The formation of these channels is similar to how the flow of the Colorado River created the Grand Canyon here on Earth.
However, scientists haven’t found conclusive evidence of any water currently on Mars. So they have looked deeper, to planets and moons further out in our solar system. In fact, they have only found liquid once, on an object a billion miles from Earth. That object is one of Saturn’s moons, named Titan. What is the liquid on Titan and could it be possible that it supports life?
Liquid Methane on Titan
No human has been to Titan and if they did, it wouldn’t be very pleasant. It smells like gasoline and is so far from the sun that the average temperature is -290 ˙F. Instead, scientists have to rely on pictures taken by orbiting satellites to study its surface. In 2007, these pictures showed large lakes on Titan. However, these lakes are made of liquid methane, not water. On Earth, methane is a gas that is burned to generate heat and light. However, because the temperature on Titan is so much lower than on Earth, molecules of methane are much closer together. They are so close to each other that methane turns into a liquid and forms lakes.
Later images showed that the methane lakes on Titan changed in size over time. Scientists wondered what could be causing these changes. They realized the lakes on Titan are part of a methane cycle, similar to the water cycle on Earth. When the methane molecules in Titan’s lakes warm up, they move more quickly and spread apart. As the molecules spread further apart, they evaporate, changing from a liquid state to a gas. This causes the lakes to shrink in size. As a gas, the molecules form methane clouds in the atmosphere. Eventually, the gas condenses and the clouds rain down liquid methane! This is just like how water on Earth evaporates from rivers, lakes and oceans to form clouds and eventually rains back down to the surface.
Could there be life on Titan?
We know that liquids, like water, have special properties that support life. Does this mean that the liquid methane lakes on Titan could support life?
Although the water and methane cycles are similar, liquid methane is much different than water. Methane is unable to dissolve and transport substances like water can. Another crucial difference is that methane is much denser than water, making it more challenging for organisms to use. Swimming in a lake of liquid methane would be like swimming in a lake of syrup, without the delicious taste. Based on these observations, scientists are unsure if methane is able to support life. Does this mean that life can’t exist on Titan? Not necessarily, as there could be life forms we have not discovered yet, that have adapted to a liquid methane environment. There is still more research to be done and other missions to explore Titan are currently in development. Therefore, while Titan is nearly one billion miles away, it may be our closest chance at finding life beyond Earth.
Tell us what you thought of this article by completing this survey!