- By Geeta Pandey
- BBC News, Delhi
An image of the Vikram lander taken by the Pragyaan rover
Last month, India made history when it became the first country to land a lunar mission near the Moon’s south pole.
Chandrayaan-3’s lander and rover — called Vikram and Pragyaan — spent about 10 days in the region, collecting data and images to be sent back to Earth for analysis.
Earlier this month, scientists put them to bed as the Sun began to set on the Moon – in order to function, the lander rover needs sunlight to charge its batteries. The country’s space research agency Isro said it hoped they would reawaken “around September 22” when the next lunar day breaks out.
Isro has been giving regular updates on their movements and findings and sharing pictures taken of them.
These updates have excited many Indians, but others have questioned the significance of these discoveries.
The BBC asked Mila Mitra, a former Nasa scientist and co-founder of Stem and Space, a Delhi-based space education company, to pick out some of Chandrayaan-3’s key achievements and explain their significance.
The distance covered – and craters avoided
Hours before the rover was put to sleep on September 2, Isro said Pragyaan “has crossed over 100 m (328 ft) and is continuing”.
It’s quite a long way to travel for the six-wheeled rover, which moves at a speed of 1 cm per second.
What is also significant, Ms Mitra says, is that it has been able to stay safe and avoid falling into the craters that dot the Moon’s little-explored south polar region.
The rover, she says, has a special wheel mechanism – called a rocker bogie – which means all its wheels don’t move together, which helps it go up and down, but it might not be able to climb out if it falls into a deep. crater. So it is important to make it go around the craters or even step back. And that, Mitra adds, is done by scientists at the command center who “see the Moon through the rover’s eyes.”
“The rover is not automated, and its movements are controlled from the command center, which acts on the basis of the images it sends.
“There is a slight delay before they reach the command center due to the convoluted route they are taking – Pragyaan passes them over to the lander, which passes them on to the orbiter to send them on to Earth.”
Isro released a graphic of the path taken by the lunar rover
So by the time the command reaches the rover, it is a few steps closer to the threat.
But the fact that it has managed to navigate safely around two craters shows that it is able to communicate really quickly with the command center, Mitra adds.
Blows hot and cold
The first set of data collected from the lunar surface and up to a depth of 10 cm (4 inches) below the surface from a probe aboard the Vikram lander showed a stark difference in temperatures just above and below the surface.
While the temperature on the surface was nearly 60C, it plummeted below the surface, dropping to -10C at 80mm (about 3 inches) underground.
The moon is known for extreme temperatures – according to Nasa, daytime temperatures near the lunar equator reach a boiling 120C (250F), while nighttime temperatures can dip to -130C (-208F). And temperatures of -250C (-410F) have been recorded at craters which never receive sunlight and remain permanently in shadow.
But, says Ms Mitra, this wide variation in temperature is significant because it shows that the Moon’s soil – called lunar regolith – is a very good insulator.
“That could mean it could be used to build space colonies to keep out heat and cold and radiation. This would make it a natural insulator for habitats,” she says.
It can also be an indicator of the presence of water ice below the surface.
A clue about the development of the Moon
When a laser detector mounted on the rover measured the chemicals on the moon’s surface near the south pole, it found a host of chemicals such as aluminum, calcium, iron, chromium, titanium, manganese, silicon and oxygen.
But the most important of the findings, scientists say, concerns sulfur. The instrument’s “first-ever in-situ – in the original space” measurement “unequivocally confirms” the presence of sulphur, Isro said.
Sulfur’s presence on the Moon has been known since the 1970s, but scientists say the fact that the rover measured sulfur on the surface of the Moon itself – and not inside a mineral or as part of a crystal – makes it “a huge feat”.
Ms Mitra says the presence of sulfur in the soil is significant on a number of counts.
“Sulfur usually comes from volcanoes, so this will increase our knowledge of how the Moon formed, how it evolved and its geography.
“It also indicates the presence of water ice on the lunar surface, and since sulfur is a good fertilizer, this is good news as it can help grow plants if there is habitat on the Moon.”
Was it really a moonquake?
The Vikram lander carries an instrument that measures vibrations derived from its own surveys and experiments as well as those from the rover and its activities.
Isro said that while the Instrument for Lunar Seismic Activity (Ilsa) had its ear to the ground, it also recorded “an event that appears to be a natural one” and investigated its source.
Isro said the lander recorded an event that “appears to be a natural event”
This event had a much larger amplitude, meaning it was much stronger, says Ms Mitra, adding that there could be several explanations for this.
“It could be some space debris – such as a meteorite or an asteroid – hitting the surface. Or it could be seismic, which would make it the first moonquake recorded since the 1970s. If so, this could lead to an explanation on what lies beneath the Moon’s surface and its geography.”
What is lunar plasma?
When Isro posted on X (formerly Twitter) that a probe on the lander had made the “first-ever measurements of the lunar near-surface plasma environment” in the south polar region and found it to be “relatively sparse”, many wondered what it meant.
Ms. Mitra explains that plasma refers to the presence of charged particles in the atmosphere that can interfere with the radio wave communications used by Chandrayaan-3.
“The fact that it is very sparse or thin is good news as it means it will interfere with radio communications much less.”
When the lander jumped
The last thing the Vikram lander did before being put to bed in early September was what Isro called a “jump experiment”.
The agency said the lander was “commanded to fire its engines, it rose about 40 cm (16 inches) and landed at a distance of 30-40 cm”.
This “successful experiment” means the spacecraft could be used in the future to bring samples back to Earth or for human missions, it added.
Could this short hop mean a giant leap for India’s future space plans?
Mitra says that “the jump test restarts the engine after a lunar landing to make sure it’s still working fine”.
It also showed that the craft has “the capability for liftoff in a lunar ground environment, as the testing and actual liftoff so far has only been from Earth,” she adds.
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