Our Solar System’s Water World

With a large portion of its surface covered by water, one would think Earth is the water world of the solar system. But Jovian moon Europa appears to hold the actual title.

Comparative volumes of water on Europa and Earth. Image courtesy NASA/JPL-Caltech

Based on the Galileo probe data acquired during its exploration of the Jovian system from 1995 to 2003, Europa possesses a deep, global ocean of liquid water beneath a layer of surface ice. The subsurface ocean plus ice layer could range from 80 to 170 kilometers in average depth. Adopting an estimate of 100 kilometers depth, if all the water on Europa were gathered into a ball it would have a radius of 877 kilometers. To scale, the above illustration compares that hypothetical ball of all the water on Europa to the size of Europa itself (left) – and similarly to all the water on planet Earth. With a volume 2-3 times the volume of water in Earth’s oceans, the global ocean on Europa is an intriguing target in the search for extraterrestrial life in our solar system.

The scene shows the stunning diversity of Europa’s surface geology. Long, linear cracks and ridges crisscross the surface, interrupted by regions of disrupted terrain where the surface ice crust has been broken up and re-frozen into new patterns. Image Credit: NASA/JPL-Caltech/SETI Institute

The above global color view consists of images acquired by the Galileo Solid-State Imaging experiment on the spacecraft’s first and fourteenth orbits through the Jupiter system, in 1995 and 1998, respectively. The Galileo mission was managed by JPL. Color variations across the surface are associated with differences in geologic feature type and location. Areas that appear blue or white contain relatively pure water ice. Reddish and brownish areas include non-ice components in higher concentrations. The polar regions (visible at the left and right of this view) are noticeably bluer than the more equatorial latitudes, possibly due to differences in ice grain size in the two locations.

Fast Facts About Europa

  1. If the sun were as tall as a typical front door, Earth would be the size of a nickel and Europa would be the size of the dome on the back of the nickel.
  2. Europa orbits Jupiter, the solar system’s fifth planet at a distance of about 778 million km (484 million miles) from the sun.
  3. One Europa day is about 3.5 Earth days.
  4. Like many other moons, Europa is locked by gravity to its planet (i.e., the same side always faces toward Jupiter).
  5. Europa’s surface is mostly solid water ice. It is extremely smooth and crisscrossed by fractures.
  6. Europa has an extremely thin oxygen atmosphere.
  7. Europa and Jupiter have been visited by eight spacecraft, which have performed flybys.
  8. Galileo is the only mission to make repeated visits to Europa.
  9. With abundant liquid water, and energy and chemistry provided by tidal heating, Europa is a promising place to look for present day life beyond Earth.
  10. If Europa’s ocean is proven to exist, it would possess more than twice as much water as Earth.
[youtube https://www.youtube.com/watch?v=3C84cYlHzn4]
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