Astronomers are excited to be poring over the first ever detailed geological map of the moon’s south polar region, where India’s Chandrayaan-3 lunar module, Vikram, touched down on August 23, 2023. The map is expected to throw new light on the moon’s origin and evolution.
Researchers from the Physical Research Laboratory (PRL) in Ahmedabad, Panjab University in Chandigarh, and the Laboratory for Electro-Optics Systems, Indian Space Research Organisation, Bengaluru, created the map using data from the rover Pragyan, which was deployed by Vikram on a nine-day mission to analyse the chemical composition of the regolith — the loose rock fragments and dust that cover the lunar surface.
Solving the magma mystery
The cornucopia of geological information from the mission has helped scientists confirm what they always suspected: the moon harbours an underground ocean of molten rock, or primordial magma. Data from previous missions, such as the US uncrewed Surveyor spacecraft, the crewed Apollo moonshots, and the robotic Russian Luna and Chinese Chang’e 3 probes, indicated the presence of such a sea of lava beneath the lunar surface. But the actual extent of magma on the moon was not known since all the available data came from landing sites near the lunar equatorial and mid-latitude regions, which are far away from the poles.
Chandrayaan-3, however, was the first mission to land in a high-latitude polar region of the moon, 630 km from the south pole, and scientists considered it the best bet to solve the magma mystery. In September 2024, a team of lunar geologists from PRL announced that the Alpha Particle X-ray Spectrometer aboard the Pragyan rover had detected magma under the landing site. This meant the ancient ocean of molten lava extended across the entire moon.
The new map of Vikram’s landing site, published in the journal Advances in Space Researchon January 20, shows an undulating landscape of highlands and low, flat plains around the lander. The researchers traced the alignment of secondary craters — dug up when debris from an impact crater lands elsewhere — and identified Schomberger to be the primary source of the debris covering the Chandrayaan-3 landing zone.
A common origin
Using the map, the scientists calculated the age of the region to be around 3.7 billion years, around the same time the first signs of microbial life emerged on the earth.
In fact, the earth and the moon have had similar evolutionary trajectories, as is evident in the dynamics of the earth-moon system. The inclination, or tilt, of the moon’s orbit is for example to the earth’s rotation and both bodies are similarly aligned to the ecliptic plane of the solar system. Their terrestrial and lunar geochemistries are also complementary, with both possessing several common isotopes, pointing to their origins from the same cloud of molten material.
Astronomers believe that some 4.5 billion years ago, when the planets of the solar system were coalescing out of the rubble floating around the sun, the young earth had collided with a massive planetary rock roughly the size of Mars. The resulting debris from the collision was flung outwards explosively, before it cooled over millions of years. This proto-planetary material gradually solidified into a molten sphere that was eventually captured by the earth’s gravity to become the moon we see today.
In those early millennia, the infant moon must have been pummelled by asteroids and space rocks as is evidenced by its surface, which is studded with numerous craters. The Vikram lander had touched down close to one of the oldest of these craters: the South Pole-Aitken Basin, which is also one of the largest impact craters in the Solar System.
Lunar craters are of great interest to astrogeologists, who study them to learn more about the evolution of impact craters elsewhere on the earth and on the inner planets of the solar system.
The cratering history
The airless and arid conditions on the moon render it a sterile environment in which craters can survive erosion for millennia — unlike on the earth where atmospheric elements abrade craters very quickly. In fact, lunar impact basins are veritable time capsules because they preserve the original records of space-rock smash-downs that occurred during the formation of the solar system.
The scientific value of lunar craters becomes even clearer when we consider how scientists can’t, even with the help of supercomputers, reconstruct the cratering history of the earth beyond a few hundred million years.
Given that lunar craters are important tools for scientists to calculate the age of geological features on other planets with solid surfaces, moon maps like the new one assume greater significance. Sadly, the “magnificent desolation” of the moon — words Apollo 11 astronaut Edwin “Buzz” Aldrin used to describe the crater-studded lunar wilderness — may not endure undisturbed for very long as efforts to colonise the moon get underway.
Littering the regolith
After the erstwhile Soviet Union’s Luna 2 lander became the first probe to ‘land’ (it was intentionally crash-landed) on the moon way back in 1959, scores of robotic and crewed spacecraft from the US, China, India, Israel, Japan, and the European Space Agency have reached the moon’s surface.
Alas, these missions have also left spacecraft components and other waste items behind, littering the regolith. It is largely unknown how the landers, rovers, and the dozen US astronauts — who planted flags, hit golf balls, drove around in rovers, and collected hundreds of kilograms of moon rock — may have disturbed the regolith, which sustains the thin lunar atmosphere. The moon’s exosphere was formed when space rocks and the solar wind, the stream of charged particles flowing outwards from the sun, kicked up the powdery dust from the lunar surface.
Scientists also worry about the contamination of lunar ice reserves by exhaust fumes from lunar landers. When a spacecraft touches down on the moon, the water vapour released from its engines spreads across the lunar surface and ends up freezing at the poles. This leads to inaccurate readings for scientists who are studying the presence and the distribution of lunar water ice. These concerns are bound to increase as more and more missions head for the moon and mining for lunar resources eventually becomes a reality.
Compacts like the Outer Space Treaty of 1967 are silent on these issues, merely making vague statements on the need to avoid contaminating space. It is high time an international legal framework is put in place to prescribe rules and guidelines for the first human colonies on the moon, which are not very far away. The sooner this is done, the better the chances of preserving the pristine nature and unique landscape of our nearest neighbour in space.
Prakash Chandra is a science writer.
Published – February 24, 2025 05:30 am IST
