Space Coasts

Ganymede, in natural light. Image captured by NASA’s Galileo spacecraft, 1996. From https://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=9003

Space coasts

Recently I was in central Florida, east of Orlando, to visit family. This area is near Cape Canaveral and the Kennedy Space Center. The barrier island has a long sandy beach where waves break onto fossil-filled ledges at low tide, a Walmart, low slung condos, schools of fish playing under piers, small beach bars, Patrick Air Force Base, and Space Coast Credit unions sprinkled up and down highway A1A. This is America’s Space Coast. It’s small town; it’s high tech.  From Cape Canaveral, SpaceX just tested a new rocket type where the first section, can make its way back to the surface, hover, and land .

In the Solar System, there are no other Space Coasts. Earth is in the “sweet spot”, the habitable zone around our star where water can exist as a liquid. Some scientists looked at the topography of Mars and say that there used to be similar coastlines there surrounding a northern ocean, although it remains to be proven.  Like Earth, Mars is also in the habitable zone, but most of its atmosphere bled into space long ago and liquid water is rare and ephemeral.   

Even though we know of no other surface water oceans (Titan, a moon of Saturn, has big lakes of liquid methane), there is evidence for layers of liquid water inside a growing number of bodies in the Solar System. Europa, a moon of Jupiter, has been long thought to have an ocean under its icy surface—if you ever watched the 1960s classic movie 2001, then you know its significance. Other bodies which may have of water within it include the dwarf planet Ceres with its water geysers, Jupiter moons Ganymede and Callisto (in addition to Europa), Saturn moons Titan and Enceladus, and, perhaps, Neptune’s Triton. Ganymede is not a small body—it is larger than Earth’s moon and the planet Mercury.

Cartoon of the results of Vance and other authors showing the interlayering of liquid water and different ice types or polymorphs. From http://www.huffingtonpost.com/2014/05/03/jupiter-moon-ganymede-ocean-life_n_5252853.html

In the journal Planetary and Space Science, Vance and other authors have modeled water’s behavior inside Ganymede. The authors, assuming that water is brackish with salts like magnesium sulfate (Epsom salt), calculate that Ganymede may have more than one ocean layer sandwiched between layers of water ice (see Figure). These ice layers are most likely different versions of the ice that we are familiar with. On the figure Ice I is ice that we are familiar with, ice that floats on water. Higher ices are stable at in the high pressures deep in the Ganymede ocean or in terrestrial lab experiments.

One of the more interesting findings is that liquid water, like on Earth, may lie on top of silicate rock deep within Ganymede. This is important as early terrestrial life may have begun in this setting on Earth, where some minerals provided the fuel to run chemical reactions.

Unlike Florida’s Space Coast, there are no palm trees blowing in the breeze and no waves breaking in the distance. On Ganymede, the meeting of ocean and land occurs in the dark at the bottom of a multi-layered ocean. But does life gather at this interface at the Ganymede equivalent of a beach-side bar? Without visiting, we won’t be able to prove if oceans or a tacky t-shirt shop can be found.

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References:

Huffington Post article: http://www.huffingtonpost.com/2014/05/03/jupiter-moon-ganymede-ocean-life_n_5252853.html

Planetary and Space Science: http://www.sciencedirect.com/science/article/pii/S0032063314000695