Water is a simple molecule, made up of two hydrogen atoms and one oxygen atom. These two elements are also some of the most abundant in the universe. But when scientists from NASA find water in worlds far away, they start thinking those worlds could support life as found on Earth.
Enceladus from Cassini (Eric J Scott / NASA via Flickr)
While exploring our own solar system, NASA’s Cassini spacecraft may have caught a glimpse of evidence for reservoirs of liquid water just below the surface of Saturn’s moon Enceladus. NASA scientists believe the water erupts in geysers that would top those at Yellowstone.
NASA even has a picture of water shooting up into space from Enceladus’s surface. Rarely has evidence of water been found so near the surface, and it raises questions about this moon.
“We realize that this is a radical conclusion—that we may have evidence for liquid water within a body so small and so cold,” said Carolyn Porco, Cassini imaging team leader at the Space Science Institute in Boulder, Colo. “However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms.”
How much water is there on Enceladus?
About a year ago, scientists at NASA said there is likely to be an entire ocean under the surface of the moon, an ocean they theorized all the way back in 2005 but that has been supported with evidence only last year.
Using brand new geophysical measurements of the internal structure of Enceladus, scientists believe an underground ocean is entirely possible. Data are consistent with the existence of a hidden ocean, and that data, from scientists’ landmark study of gravity measurements, was published in the April 4, 2014 edition of the journal Science.
“The way we deduce gravity variations is a concept in physics called the Doppler Effect, the same principle used with a speed-measuring radar gun,” said Sami Asmar of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., a coauthor of last year’s study. “As the spacecraft flies by Enceladus, its velocity is perturbed by an amount that depends on variations in the gravity field that we’re trying to measure. We see the change in velocity as a change in radio frequency, received at our ground stations here all the way across the solar system.”
Where else is there water in the universe?
A little closer to Earth, NASA’s Curiosity Mars Rover discovered an ancient streambed that existed when conditions on the planet would have been favorable for life as we know it.
Then, NASA’s Spitzer Space Telescope has observed evidence that storms of water-rich comets have been bombarding young planets in other solar systems, flushing them with water, similar to the way planets in our own solar system were bombarded billions of years ago.
The presence of liquid water is closely tied to the possibility of life on exoplanets. In order for life as we know it to exist, liquid water must be present. Solid water (ice) and gaseous water (vapor or steam) just won’t work to support life.
That’s because each solar system has what’s known as a “habitable zone,” which is the orbital distance from the star at which water can exist in liquid form. Planets that are too far away from a star will be too cold; planets too close to a star will be too hot.
Importance of water to life as we know it
Neither a hot planet nor a cold planet would be able to support life as we know it, because life like ours requires liquid water, which doesn’t exist at extreme temperatures:
- Water is the only chemical compound on our planet’s surface that comes naturally in all three physical states.
- Water is an excellent solvent, dissolving a wide array of chemicals, which serve as reactants to the biochemical reactions that sustain life. As these chemicals dissolve in liquid water, they react with one another.
- Liquids are fluid, always moving around. Thus, water helps dissolved molecules get to where they need to be to react with other dissolved molecules. For us, it’s important that water can easily move through cell membranes.
- Water has a high specific heat and can buffer extreme changes in temperature that might destroy life, such as heat from a chemical reaction or a star’s radiant energy.
The specific heat of a substance is the quantity of heat per unit mass needed to increase the temperature of the substance by one degree Celsius. For water, with a specific heat of 4.186 Joules per gram-degree Celsius (1.0 cal/g°C), higher than any other common substance, you need to add or remove a lot of heat energy before any significant temperature change is seen, and for exothermic or endothermic biological reactions, that’s an important feature.
where Q is the heat added in Joules, m is the mass of the substance being heated, ΔT is the change in temperature in degrees Celsius, and c is the specific heat of the substance in J / g °C.
