Seismic experiment might reveal thickness of Europa’s ice

SALT LAKE CITY— A literal moonshot just might reveal the thickness of Europa’s icy crust.

A new plan to launch an SUV-sized rocket canister at Jupiter’s famous, frigid moon could shake the surface so much that the tremors would be visible from space, said mechanical engineer T.J. Campbell of the Catholic University of America in Washington, D.C.

A spacecraft flying overhead could record the tremors, which might help scientists figure out how thick Europa’s ice shell really is, Campbell and colleagues proposed May 24 at a meeting of the Acoustical Society of America. Estimates range from a few kilometers to more than 30 kilometers (SN: 5/17/14, p. 20).
NASA has a concept for a Europa mission in the works: It’s called the Europa Multiple Flyby Mission, and it would launch in the early 2020s. The plan is to use ice-penetrating radar to probe the shell (SN Online: 5/26/15), but that might not work on ultrathick ice, Campbell said. So his team came up with a seismic approach. Instead of discarding the empty propellant tank needed to blast the spacecraft from Earth’s orbit to Jupiter, the team wants to crash it into Europa. “We can put it to use,” he said. “Let’s make it hit the surface.”

NASA, though, typically avoids crashing objects into environments where life might thrive for fear of contaminating an alien world. A propellant tank sent to smash into Europa would have to be heavily sterilized first.

Scientists could time the impact so that the spacecraft was nearby to watch. Campbell and colleagues estimated that the tank would slam into Europa’s crust at about 15.7 kilometers per second (roughly 60 times faster than the cruising speed of a 747 airplane). Such an impact would gouge out a crater and send waves of energy racing through the ice like the tremors of an earthquake. The slower the waves, the thicker the ice.

Campbell’s team computed that the waves might be large enough to be seen by a spacecraft some 2,000 kilometers away. In real life, though, capturing the waves on camera depends on all sorts of factors, Campbell adds, from the spacecraft’s imaging techniques to how the ice actually responds to the impact.

Editor’s Note: This story was updated May 25, 2016, to include NASA’s position on crashing objects into other worlds.