Swirls are a rare lunar surface feature, bright and curvy shapes on the lunar soil. Seen below are a swarm of lunar swirls in the Ingenii crater.
Lunar swirls are brighter than their surroundings despite having the same composition. Unlike the rest of the lunar surface, material within the swirls is not exposed to the constant weathering from solar wind and meteorites. This means the material remains fresh/bright for a long amount of time. But what protects the material from the harsh lunar environment? Local magnetic fields!
The Moon doesn’t have a global magnetic field (it might have had in the distant past) but it does have local magnetic anomalies. Interestingly, all swirls on the Moon are associated with a local magnetic field. These local magnetic fields provide protection to the swirl surface from solar radiation and help retain its bright, distinct look. On the other hand, regions besides the magnetic field lines get accelerated radiation weathering and are thus darker. How do such swirls form though?
Mare Ingenii is a case of scattered, magnetized swarm of lunar swirls spread across more than 100 km. It is one of key scientific places to visit on the lunar farside. NASA chose Ingenii as a landing site for the Constellation Program.
To get an understanding of the swirl formation processes, we need precise measurements of the local magnetic field strength across the swirl. We also need to measure the solar wind interaction with the swirl’s magnetic field, and see how the local plasma environment is shaped by the field. A landing mission to Mare Ingenii would be key to understanding the nature of lunar swirls and the Moon's evolution.