The Perseverance instrument that serves as a ground-penetrating radar is RIMFAX.
RIMFAX stands for Radar Imager for Mars’ Subsurface Experiment. Mounted near the rover’s lower rear, it sends radio waves into the ground and measures returning reflections. Those signals reveal boundaries between layers and materials beneath the surface, giving scientists a view of geology that cameras cannot provide.
The instrument can help identify buried rocks, sedimentary layers, lava-related features, and other subsurface structures. By comparing radar profiles with exposed rocks and surface images, researchers can reconstruct how Jezero Crater’s landscape formed and changed over time. Subsurface layers may preserve evidence of ancient water activity that has been erased or obscured at the surface.
RIMFAX was developed with major contributions from Norway’s Norwegian Defence Research Establishment. Its name echoes Hrímfaxi, a horse from Norse mythology associated with bringing night. The instrument is not a metal detector or a direct underground camera: it produces radar data that scientists interpret as a layered profile. Mastcam-Z is an imaging system, MEDA studies weather and dust, and PIXL analyzes elemental chemistry on rocks.