For the Crater Good

More than five hundred million miles away, there's a moon orbiting Jupiter with the smoothest surface of any known solid object in our Solar System. That surface is made of ice and laced with cracks; hiding below is a liquid ocean kept warm by the energy of a rocky core. Like an enormous chilly gyroscope, the ice shell rotates around the moon's center, while the moon hurdles around the gas giant. 

Some scientists suspect life may be hiding in that icy ocean. 

In March 2020, I met with physics student Mikayla Huffman and geology professor Dr. Jon Kay to talk about crater formation on this icy moon (and similar bodies). Using supercomputers and a simulation technology called iSALE, Jon and Mikayla's research explores how meteor collisions can leave different shaped craters, depending on the structure of the surface. Their ultimate goal is to make something akin to a scout's guide for animal tracks, but instead of using shapes in the mud to know what kind of animal passed by, the shapes of the crater can indicate if a planet or moon's surface has liquid water (or slushy ice).

Here's a quick example to illustrate: If you throw a rock into sand, it leaves a very different impression than if you were to throw it into mud. In essence, Jon and Mikayla used iSALE computer code to throw a bunch of rocks (technically, a 0.62 kilometer-wide ice ball going 15 kilometers a second) into a bunch of different icy/watery/slushy terrains. After, they scrutinize at the simulated carnage and piece together patterns from the results.

In terms of Europa, these simulations can illuminate what the icy crust of Europa (and other moons) is really made of. Is it like a loaf of sourdough bread, with uneven pockets of air spread out in the ice? Perhaps large liquid lakes are suspended in the ice? Or maybe Europa is like a frozen over slushy? We just don't know.

Why do we care? Rocks crash into other rocks, into moons, into planets all the time. What's the fuss over some lunar potholes?

Besides being able to simulate HUGE explosions (pretty awesome in its own right), these simulations shed light on how the icy outer layer of the Moon transforms into an inner ocean. If a plumbing system exists between the inner water and outside space, or if liquid lakes of water are embedded in the ice, then the odds of life on Europa get a hell of a lot better.

If  biologically useful materials can move from the surface, through the ice, and into the subsurface ocean, then life may take advantage of such resources.