Cities are growing. Forests are shrinking. But what’s happening beneath our feet—in the soil of the very trees that line our streets and parks—may be even more critical to the planet’s future than we realize.

Penn geophysicists Hugo Ulloa and Douglas Jerolmack and colleagues have uncovered Earth-sculpting processes that result from the formation of snowball-like aggregates they call “sandballs” that take on two shapes: peanut-shaped structures with liquid cores and stable, donut-shapes—with airy centers—that behave like rigid solids. Their findings provide fundamental insights into erosion and will broaden scientific understandings of landscape change, soil loss, and agriculture.

Researchers typically analyze images taken by geostationary satellites to identify regions of the sky where contrails form, but new research shows adding images taken by low-Earth-orbiting satellites would help identify many more such regions. Pilots could avoid these regions to reduce aviation’s climate impact.