Entering a planet’s atmosphere is a dangerous maneuver for any spacecraft, as it must withstand the intense frictional heat generated by high-speed contact with atoms and molecules.

That’s why landers and rovers have heat shields. And new research from the Grainger College of Engineering at the University of Illinois Urbana-Champaign suggests that an atmosphere’s composition has a big impact on how heat shields work.

A heat shield “breathes” when it hits the atmosphere. The surface of the shield begins to burn away, in a process called ablation. To mimic the hypersonic speed of a spacecraft’s entry, a team of researchers led by Francesco Panerai, a professor in the Department of Aerospace Engineering, experimented with heat shields in the Plasmatron X wind tunnel at the Center for Hypersonics and Entry System Studies, which is housed a few blocks from the university’s campus.

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“What was very surprising about the study is that, when we changed the gas, the ablation phenomenon behaved in different ways,” Panerai said in a March 12 statement. “In a classical air environment where you have oxygen present, the ablation happens in a steady way. The flow around the spacecraft erodes the surface, and particles get ejected as a constant stream.”