Moons with Water : The Solar System is Wet

Astronomers continue to discover new moons with water in the solar system, what else is hiding in the vast oceans below their frozen surfaces? Could we find life on another planet in our solar system?

Since our statistical sample of planets with life is severely limited (still just the one) we’ve adjusted our search to rely on substances, and properties, we know are required for life here on earth. One substance believed essential for life, at least as far as we know, is water. The search for water focused on Mars for a long time but now that focus have shifted to the moons of the giant planets in the outer solar system.

In the late 1870s the astronomer Giovanni Schiapparelli reported observations of canali, channels, on the surface of Mars. A mistranslation of this observation, to canals, inspired writers to create books taking place on Mars involving sentient life native to the planet. This strange new world captured the imagination of the public, and later drove scientific exploration of the red planet. Not until the 1960s, when space craft were sent to explore the red planet did we find that Mars was a sterile desolate world. Though the atmosphere have some water vapor and the poles consist of water ice, any free flowing water on Mars probably disappeared millions of years ago. Even lacking in water, Mars has another distinction, being the only planet in the solar system inhabited solely by robots. So if not Mars, where is the water?

It seem the answer is: Under the surface of frozen moons.

Moons with Water Under a Frozen Surface


moons with water

NASA/JPL/University of Arizona

Europa, a moon of Jupiter, were for decades considered the prime candidate for life in our own solar system. For a long time this moon was thought to be the only other planetary body in the solar system with liquid water. Not only a moon with water, this satellite is believed to have all three requirements for life; liquid water, an energy source and organic molecules. The evidence for a subsurface ocean rests on three pillars.

  • The Galileo spacecraft detected signs of an induced magnetic field, evidence of an conductive substance less than 30 km below. What conducts electricity? Salt water.
  • Europa has a scarred surface of ridges and bands hinting that kneading by Jupiter’s gravity or heat from geothermal sources have cracked and refrozen the surface over and over.
  • The large scale fractures on the surface suggests that the surface has slipped relative to its interior, hinting at the existence of a hidden ocean beneath the ice.


moons with water

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

As vast oceans goes, Europa recently got competition from Saturn’s moon Enceladus, and was surpassed by the manner of it was discovered. In 2005 the Cassini spacecraft detected huge plumes of water spewing from the surface of the moon. Plumes consisting of extremely minute ice water particles, rocks and various gases spraying out at a velocity of 400 meters per second. A recent study  based on data collected by the Cassini spacecraft revealed that the water plumes contained evidence of the moon being the only other planetary body in the solar system with active hot water chemistry. One instrument on the space probe detected silicon rich rock particles spewing from the surface inside the water plumes. These rock particles could only form at temperatures above 194 degrees Fahrenheit (90 degrees Celsius ).


moons with water

Credit: NASA, ESA, and G. Bacon (STScI)

The most recent moon possibly having water was actually performed with a telescope. The Hubble space telescope have detected evidence of an underground salt water ocean on Ganymede by looking at its “northern lights”. Observations hint at Ganymede having not just a little, but more water than all of earth’s oceans combined. This “dowsing” was made possible by watching the rocking motions of two aurorae around the moon. This observation used the same principle as the one finding water on Europa. A salt water ocean would disrupt magnetic fields and if a saltwater ocean is present on Ganymede the resulting magnetic field would counter Jupiter’s magnetic field.  This resulting “magnetic tug-of-war” would suppress the rocking of auroraes surrounding the moon, exactly what astronomers saw, hinting at a vast hidden ocean.

Future Missions

Many possibilities, but as always a finite amount of cash. The cost of an unmanned planetary mission to one of these potentially watery moons are estimated between $425 and 500M. Though no mission to any of these satellites are fully funded today one proposal is called the “Europa clipper”. In this proposed mission a probe perform 45 flybys of Europa to precisely map the moon and determine the thickness of the ice shell as well as other geographic data. The mission is currently in the early planning phase and at this time there isn’t enough cash to see it through to the end. A further complication is that congress have appointed a science denier to oversee NASA as well as science programs.

On a positive note NASA did get some extra funds at the tune of $530M in December 2014 to support the development of the Space Launch System rocket, an extremely powerful rocket needed for travel to the outer solar system, and planetary science program.

The quest to find moons with water continues and one thing is certain: Where we find warm water there’s a good chance we’ll also find life. If that happens, either on these moons with water, or elsewhere, it would change both how we view the universe and our place in it.