Korean lunar orbiter reveals Moon's far side is inexplicably more conductive

Stephen Luntz
IFL Science
Mon, 18 Dec 2023 01:42 UTC

© NASA via wikimedia commons

We've known for almost 60 years that the far side of the Moon has almost no seas, but it's only know we have learned it is more conductive than the near

It's just one of the intriguing things the Danuri orbiter has revealed that previous missions missed.

There's something odd about the far side of the Moon, scientists have concluded based on data from the Korean Pathfinder Lunor Orbiter. The results are yet to be published, but suggest a discrepancy between the conductivity of the near and far sides, which so far lacks a plausible explanation.

Lunar exploration is becoming a global affair. Along with missions from the United States, China, India and Japan, the Korean Aerospace Research Institute has had an orbiter around our satellite for a year. Nicknamed Danuri, the mission is proving there is plenty the larger nations have missed.

Although the Institute is coy on the results over that time, Nature has been given advance notice of some of what has been found.

The major discovery was made in conjunction with two of NASA's smaller satellites. The Moon does not have a global magnetic field the way the Earth does, although it once did. However, like Mars, it has some intriguing local fields.

Magnetic anomalies in lunar swirls interest planetary scientists so much NASA has considered a mission purely to explore them, using two small satellites tethered together across 180 kilometers (112 miles). Photographing the most famous of these, the Reiner Gamma Swirl in exceptional detail, was one of Danuri's first achievements.

© NASA/Lunar Reconnaissance Orbiter

The Reiner Gamma "swirl" seen on the Moon's surface. Swirl formations are associated with anomalies in the moon's magnetic field.

Unexpectedly, however, Danuri has found more widespread magnetic fields on the far side, which indicate greater conductivity deep within the Moon there. Professor Ian Garrick-Bethell of the University of California, Santa Cruz, told Nature this "doesn't make sense." The two reasons scientists can think of would be if the far side was hotter, or if there was more water under the surface on that side.

The latter would be of great interest to future missions looking for the most precious of resources, but no reason has been proposed for why it should be true. Simply facing away from the Earth seems unlikely to produce such an effect.

The mission also carries a gamma-ray detector, which allowed it to pick up the Brightest Of All Time gamma ray burst while still on the way to the Moon in October 2022.

A more anticipated success from the project involves exploring the depths of craters near the Moon's poles. These are of interest to astronomers because ice is thought to survive at the bottom. However, the same lack of sunlight that has ensured the ice's longevity also makes these areas hard to see. Dunari's "ShadowCam" is so sensitive it can photograph these locations using light from the Earth or scattered off nearby mountains far better than anyone has before.

© Mosaic created by LROC (Lunar Reconnaissance Orbiter) and ShadowCam teams with images provided by NASA/KARI/ASU

The Shackleton crater photographed by the ultra-sensitive Shadowcam, revealing features that would be too dark for other cameras to see.

Without the resources to send people to the Moon, at least soon, nations like South Korea are seeking to fill scientific niches left unoccupied by the big space powers. Most of these relate to high latitudes, so Danuri is in an orbit that takes it over the poles, rather than in a more equatorial orbit as initial lunar missions favored. The team behind the mission also realized no one had yet used cameras that measure polarized light as a way to investigate the magnetism of the lunar surface, so they seized the opportunity.

The mission was originally scheduled to end this month, but has now been extended to December 2025. That will, however, require it to survive lunar eclipses (which from its perspective will be solar eclipses) in March and September 2025. Each will cut off its access to sunlight for longer than its usual trip into the Moon's shadow. The partial eclipse this year proved no problem, but the deep total eclipses may strain the orbiter's batteries.