An international team of researchers has attempted to artificially recreate the material that coats the surface of certain bodies without atmospheres in the Solar System, finding some indication that their surfaces might be a lot more porous than previously thought.
As reported in the journal Icarus, the team constructed artificial regolith, the top layer of soil on space rocks, using aluminum oxide grains of different sizes. They then observed how sunlight reflects off these different bits of material. After comparing their analysis to observations of real space objects, the team suggested that the material might have a low-density surface.
The study suggests the objects are covered by regolith, which is less dense than freshly fallen snow. If this is the case, future landing missions to Europa will need to take this into account. A soft, fluffy surface has also been theorized for the dwarf planet Ceres, the largest object in the Asteroid Belt. Evidence suggests that it could retain 77 percent of an impactor’s mass if it were to be struck.
Concern about landers sinking into bodies in the Solar System is nothing new. In the early days of space exploration, there were worries that even our own Moon would be too soft to land something on. So while the observations suggest a certain scenario, we don't have a complete picture of these bodies just yet.
“Of course, before the landing of the Luna 2 robotic spacecraft in 1959, there was concern that the Moon might be covered in low-density dust into which any future astronauts might sink," lead author Robert Nelson, from the Planetary Science Institute, said in a statement. "However, we must keep in mind that remote visible-wavelength observations of objects like Europa are only probing the outermost microns of the surface."
More information about Europa’s surface will come from the European Space Agency's JUICE mission and NASA’s Europa Clipper. The latter will be especially useful as it will be equipped with an infrared spectrometer and a radar that can penetrate through surface ice, providing the right suite to find out exactly what the shell of such an object is like.