Alien Quicksand Could Sink NASA Landers on Jupiter's Moon Europa

NASA wants to send a spacecraft to orbit Europa, shown here with Jupiter but not to scale, sometime in the 2020s. NASA/JPL-Caltech

If NASA ever wants to land on Jupiter's potentially life-supporting moon Europa, it may need to figure out a way to avoid sinking straight down into the moon's interior like a person falling through quicksand. That's because the moon's surface may have more holes in it than actual mass, according to a new paper published in the journal Icarus.

The concerns may also apply to a host of other worlds, including Europa's neighbors Io and Ganymede, plus asteroids like Nysa and Angelina.

Since we've never actually visited any of these worlds, the hypothesis is just one possible explanation to address the remote sensing data spacecraft have gathered. Those data only describe the top fraction of an inch of surface of Europa and its fellows, and they actually measure how light hitting the surface at different angles bounces off the material.

That means there's no way of knowing right now whether the mostly-air material is a thin flurry covering a more solid surface or if it goes on for inches or even feet into these bodies. (In fact, scientists had similar concerns about our own moon before the first lander touched down on it.)

What the team behind the new paper actually did was try to model surfaces in labs here on Earth and see how closely they could match the qualities measured on distant worlds. That meant using a compound called aluminum oxide, which scientists can buy in sandy mixes sorted by size. The compound happens to form crystals with a similar structure as ice, which astronomers have already identified on these worlds.

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So they took different size grains of aluminum oxide to mimic the surface of Europa and similar places. They found that as the grains got smaller, the amount of space between them increased—when they used the finest sand they had, the overall structure was almost 98 percent empty. That's because of the way individual particles interact with each other, they realized.

And they found that this sort of structure, with very small particles and very large empty spaces, seems to reflect light in a similar way as the uppermost surface of Europa, some of Jupiter's other moons, and some asteroids, suggesting their uppermost surface may be extremely porous.

Right now, NASA doesn't have any concrete plans to touch down on Europa's surface, although the agency does want to send a spacecraft to circle the moon 40 or more times. That mission, called Europa Clipper, is due to launch sometime in the 2020s, and NASA is supposed to unveil an initial design for the spacecraft later this year.