On Earth, seismometers around the globe can monitor and track earthquakes. With multiple locations, the instruments can provide extremely precise information about the size and location of a shakeup. By calculating how long it takes a seismic wave to travel through the crust to two (or more) locations, geologists can determine the planet’s composition and spot any interior structures that lie along the path.Things will be more challenging on icy moons. Because weight is limited and the competition for instruments is fierce, initial visitors to worlds like Europa will most likely contain only a single accelerometer. Accelerometers , which detect ground movement, are more general than earthquake-tracking seismometers. Though less sensitive than the alternative, accelerometers can study localized disturbances in greater depth.An accelerometer placed on the surface of Europa — with, say, a lander — should be able to measure the thickness of the ice and the ocean beneath. It could even capture the sound of waves lapping against the ice. These sloshing ocean sounds could reveal how much turbulence occurs between the two, possibly driven by geologic activity further beneath the water.But we may not have to probe all the way to the ocean to find liquid water. In 2011, Schimdt proposed that features on Europa’s surface could be related to subsurface lakes of liquid . By comparing the features to those found in Antarctica, her team suggested that as stress fractures in the ice fill with water, the weakened material collapses, creating the observed features. That water could come from shallow lakes — lakes that an accelerometer could spot.An accelerometer could also reveal insights about the moon’s fracture-covered surface. As the Europa orbits Jupiter, the changing gravitational forces cause it to stretch and relax, cracking the crust. An accelerometer could identify these changes and use them to determine the characteristics of the icy outer layer.At a recent meeting discussing the proposed Europa lander, Schmidt suggested that the spacecraft could use its arrival to measure the nature of the surface. While most instruments would likely be turned off during the landing, if an accelerometer was powered up, it’s possible that it could detect the blasted off skyhook proposed to lower the lander, much like the system used to lower Curiosity to Mars’ surface. After the lander touched down, the jettisoned skyhook would land on another part of the moon. If the accelerometer could record the crash, whose position and velocity could be calculated, it could provide even more insights into the nature of Europa.