Pieces jettisoned by the Perseverance mission accidentally transformed the Martian surface into an experimental site.
When Perseverance arrived on Mars in 2021, the vehicle abandoned several components that were no longer needed. Two 77-kilogram tungsten masses were used to balance the craft during its journey. Fragments of the cruise stage also fell. Hitting Mars at several kilometers per second, this debris carved five small craters.
Artist's view of the deployment of Perseverance's supersonic parachute during its descent through the Martian atmosphere.
Credit: NASA/JPL-Caltech
These impacts offer researchers a rare opportunity. When a meteorite creates a crater, its mass, speed, and trajectory generally remain poorly known. Here, scientists had information about the hardware sent to Mars. They could therefore compare the predicted impacts more precisely with the traces actually left on the ground.
Researchers located the craters using images taken from Martian orbit. They are situated northwest of Jezero Crater, explored by Perseverance.
Two craters, produced by the tungsten masses, were used to test the terrain's strength. Researchers recreated the collisions by computer. Their calculations match the observed craters when the ground has a cohesion of about 7 kPa, with an uncertainty of 1.5 kPa. This value corresponds to a poorly consolidated material.
Impact sites of the ballast blocks jettisoned by the Mars 2020 spacecraft during the landing of the Perseverance rover. The visuals detail the Jezero Crater region, the nature of the soils, the expected impact zones, and close-up images of the impact craters.
Image: NASA/JPL/University of Arizona.
A surprise emerges when the usual methods for predicting crater size are used. Under these particular conditions, they produce diameters up to about ten times too large. The projectiles were very dense and arrived at a shallow angle. They therefore penetrated deeply into the ground, which the commonly used equations describe poorly.
In other words, crater size does not depend solely on the energy delivered. The nature of the projectile and its angle of arrival also matter greatly. This difference can skew estimates of the terrain's strength if a formula developed under different conditions is applied directly.
This debris could now inspire ideas for future missions. The authors propose deliberately using certain components jettisoned by spacecraft as scientific projectiles. With a known trajectory and mass, the resulting craters could be used to study the upper layers of the ground on Mars or other celestial bodies.