Sand on Earth is continually created by the slow erosion of rocks. But on Mars, violent asteroid impacts can play an important role in the formation of new sand.
Up to a quarter of the Martian sand is made up of spherical chunks of glass forged in the intense heat of impacts, a new study shows. Since windblown sand sculpts the Martian landscape, this discovery reveals how Asteroid impacts help shape Mars, even long after the collisions occur, Purdue University planetary scientist Briony Horgan and colleagues suggest. The team will present their results on August 18 at the 85th Annual Meeting of the Meteoritical Society in Glasgow, Scotland.
Using data collected by spacecraft orbiting Mars, Horgan and his collaborators looked at different wavelengths of visible and infrared light reflected from the planet’s surface to determine the minerals present in the Martian sand. The team found traces of glass all over the planet, particularly at higher latitudes.
One explanation for all that glass is volcanic eruptions, which are known to produce glass when magma mixes with water. But the glass-rich swath of Mars, the planet’s northern plains, is remarkably devoid of volcanoes, the researchers note. That rules out volcanic eruptions as the culprit there, and instead suggests that many more cataclysmic events (asteroid impacts) could be involved.
That’s a plausible argument, says Steven Goderis, a geochemist at the Vrije Universiteit Brussel in Belgium who was not involved in the research. “Mars is often seen as a volcanic planet. But there is also a very strong impact component, and this is often overlooked.”
When an asteroid moving at several kilometers per second collides with a rocky planet like Mars, the energy from the event melts nearby rocks and launches them skyward. That molten shrapnel fragments, producing sand-grain-sized pieces that are roughly spherical. Those pieces of glass, called impact spheres, eventually Rain back to the planet (Serial number: 03/31/21).
In the last 3 billion years, asteroid impacts could have covered the surface of Mars in a layer of impact spheres about half a meter thick, Horgan and colleagues calculate. All of that material added to the sand on Mars that formed through normal erosion. “The impacts helped deliver sand to the surface continuously over time,” says Horgan.
Scientists may have the opportunity to analyze Martian impact spheres in the future. NASA’s Perseverance rover is currently storing samples of martian sand and rocks for an eventual return to Earth (Serial number: 9/10/21). That’s exciting, says Horgan. “The record of all this is in the sand.”