Hypotheses for the formation of Swirls
(1) Attenuated space weathering due to solar wind shielding. Models for creation of the magnetic anomalies relevant to the swirl formation, although independent of the swirls' optical characteristics, point to that, several of the magnetic anomalies are antipodal to the younger, large impact basins.
Once the magnetic anomaly is installed, the swirls are formed because they are protected from the solar wind. In this process, the swirls represent exposed silicate materials whose albedos have been selectively preserved over time from the effects of space weathering via deflection of solar wind ion bombardment. According to this model, optical maturation of exposed silicate surfaces in the inner solar system is, at least, partly a function of the solar wind ion bombardment.
This model suggests that swirl formation is a continuing process, which began after placement of the magnetic anomaly.
(2) Disturbances caused by comet impacts. Magnetization of these antipodal regions could occur in the presence of an amplified magnetic field. This one would result from a plasma cloud generated by the impacted basin with a weak magnetic field present into the Moon at the time of its formation.
For the comet impact model, the high albedo of the swirls is the result of scouring of the top-most surface regolith by the results of coma’s turbulent flow of gas and dust. These "news" exposed fresh materials are redeposited in discrete deposits.
The magnetization of near-surface materials, heated above the *Curie temperature* through hyper-velocity gas collisions and micro-impacts as the coma impacts the surface, create the associated strong magnetic anomalies.
Proponents of the comet impact model consider the occurrence of many swirls antipodal to relatively young, major basins to be coincidental or the result of incomplete mapping of swirl locations.
(3) Electrostatic dust accumulation. An unusually thick and/or strongly magnetized deposit of basin ejecta has been invoked to explain swirls that are not antipodal to a basin. In this case, the Reiner Gamma Formation is a good example.
Another explanation could be the dust transport model. It propose that, the weak electric fields created by the crustal magnetic anomalies and the solar wind plasma could attract or repel the fine dust electrically charged. These finest particles of lunar soil have high albedo that could be the result of electrostatic movement of dust lofted above the surface during terminator crossings. That could cause this material to preferentially accumulate and form the bright, looping swirl patterns, as seen below.
(4) Collapse of fairy-castle structure. An alternative model to a plasma-induced magnetic anomaly, but which also draws upon the basin-antipode correlation is by impact-induced currents and seismic waves ringing the planet
MAGNETIC ANOMALIES AND SWIRLS - 59°W, 7.5°N - REINER GAMMA
The Reiner Gamma Formation is centered in the Oceanus Procellarum on the near the visible side of the Moon, with an extension of about 30 by 60 km.
The Reiner Gamma formation (7.4 N, 300.9 E) is an example of a lunar swirl. Pictured here on the left-hand side of the image. Reiner Gamma is named after the Reiner impact crater shown for comparison on the right. The crater is 117 km to the east and has diameter of 30 km with a depth of 2.6 km. By contrast, the unusual diffuse swirling of the formation and concentric oval shape has fluidlike wisps that extend further to the east and west. Its distinctive lighter color stands out against the flat, dark surface of Oceanus Procellarum. Unlike crater ejecta, the shape of the formation appears unrelated to any topographic structures that would account for its presence.
Image courtesy of NASA.
Because Earth's solid iron inner core rotates inside a molten outer core, a magnetic dynamo is created and generate a global magnetic field, an magnetosphere. Extending up to 50,000 miles above the surface, this magnetic field traps and redirects the constant stream of charged particles from the sun, aka the solar wind.
The Moon doesn't have a global magnetic field, so its surface is constantly being bombarded by the sun's charged particles.
But, the India's Chandrayaan-1 lunar probe has confirmed that the Moon have a miniature version of a magnetosphere covering a small pocket in the northeastern region, the farside .
However, the magnetic field at the center of the bubble is 300 times lower than the Earth's one over the Equator and 600 times lower than the Earth's Poles.
Lunar swirls are bright, wispy patterns on the lunar surface that stand out against the otherwise dark lunar soil, like hundred-kilometer-wide bleach stains, seemingly unrelated to the local topography. Over a dozen swirls have been discovered on the Moon, but scientists haven’t agreed on an explanation for them.
Each swirl marks the location of a magnetic anomaly, or “mini-magnetosphere”—a bubble of magnetic field lines shaped like an egg-beater rising out of the lunar surface. One theory is that these magnetic anomalies—whose origin is also a mystery—might somehow protect the areas they cover from space weathering, while the rest of the surface is darkened by the impact of the solar wind. The possible reason is it should be impossible for a mini-magnetosphere to deflect all particles in the solar wind, like the Earth’s magnetic field does. The magnetic field around a lunar swirl isn’t strong enough to deflect protons, given the size of the protected region.
Two swirls on the lunar farside lie directly opposite nearside impact basins (Mare Imbrium and Mare Orientale), suggesting that their formation and that of the localized magnetic fields is related to the impacts that created the basins. Reiner Gamma does not have a corresponding impact basin on the farside. In addition, there appears to be no correlation between the Reiner Gamma swirl and its local topography.
Reiner Gamma's magnetic field strength is approximately 15 nT, measured from an altitude of 28 km. This is one of the strongest localized magnetic anomalies on the Moon. The surface field strength of this feature is sufficient to form a mini-magnetosphere that spans 360 km at the surface, forming a 300 km thick region of enhanced plasma where the solar wind flows around the field.
Every swirl has an associated magnetic anomaly, but not every magnetic anomaly has an identifiable swirl.
Credit: NASA/GSFC/Arizona State University
It is almost confirmed that the lunar swirls are associated with magnetic anomalies. Some of these swirls, such as Mare Ingenii at right and Mare Marginis in left below, are ‘antipodal’ to large impact structures, that is just in opposite regions.
But, for other like Reiner Gamma, the swirls correspond to magnetised materials in the crust or iron-rich ejecta materials able to deflect the solar wind. This would prevent surface materials to undergo maturation processes, and so produce an optical anomaly.
The analysis of NASA’s spacecraft Clementine imaging data showed that the optical and spectroscopic properties of the local regolith surface layer are close to those of immature mare crater-like soils. This is consistent with the properties of a shallow subsurface mare soil layer.
Also, some considerations about an impact crater support that, the uppermost part of the regolith could have been modified through an interaction with falling fragments of a low-density comet nucleus, previously broken by tidal forces and having ploughed the regolith.
The major focus about the explanation of Swirls in the Reiner Gamma Formation is that the magnetic anomaly would not be the result of an antipodal crustal field generated in the formation process of large impact basins. It would rather arise from local effects during the interaction between the lunar surface and cometary physical environment, with the possibility that the solar wind is locally deflected and contributes to the unusual optical properties.
So, the Reiner Gamma Formation could be an interesting site for future human exploration because of the radiation deflected from the surface. Further testing of this hypothesis requires access to the physical properties of the surface to constrain the mechanisms of formation of the lunar swirls.
Key Measurements suggested could be the near-surface plasma environment, the volatile signature (OH/H2O), the magnetic field strength and direction, radiation measurements, the solar wind monitoring, high-resolution imaging, regolith properties and the dust environment, and quantify regolith geo-mechanical properties.
A roving mission trough a swirl could take in-situ measurements of the magnetic field and plasma environment across the bright and dark lanes.
THE SECRET OF THE DARK SIDE OF THE MOON
Earth's gravity is so strong we only see one side of the orbiting moon. Modern exploration to the mysterious dark side revealed dramatic surprises and revised theories about the moon's formation.
Credit: Science Channel
MAGNETIC BUBBLES ON THE MOON REVEAL EVIDENCE OF "SUNBURN"
Credit: NASA's Goddard Space Flight Center/Genna Duberstein
Every object, planet or person traveling through space has to contend with the Sun's damaging radiation -- and the Moon has the scars to prove it.
Research using data from NASA's ARTEMIS mission — short for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun — suggests how the solar wind and the Moon's crustal magnetic fields work together to give the Moon a distinctive pattern of darker and lighter swirls. Lunar swirls, like the Reiner Gamma lunar swirl imaged here by NASA's Lunar Reconnaissance Orbiter, could be the result of solar wind interactions with the Moon's isolated pockets of magnetic field.
In physics and materials sciences, the Curie temperature (TC), or Curie point, is the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism.