India’s Moon Milestone Year: All The Science That Came Out Of Chandrayaan-3 In 2023

Twenty-twenty-three was the year India touched down on the Moon with all the poise and confidence of a thriving ancient civilisation.

After it became only the fourth country ever to soft-land — that is, achieve a controlled landing — on the Moon on 23 August 2023, India became an undeniable space power.

Upon landing on the lunar surface, the Chandrayaan-3 mission turned quickly from pilot to scientist, carrying out scientific studies over the duration of one lunar day or two Earth weeks (in actuality, for about 10 days).

The mission was armed with two excellent assistants to help with the science — the Vikram lander and the Pragyan rover, both equipped with advanced tools of their own in the form of scientific instruments, or "payloads," to get the job done.

All the payloads were switched on for work on 24 and 25 August and remained in operation until they were put to bed on around 4 September.

So, what science did the Chandrayaan-3 robotic scientists unearth from the lunar surface during this period? As the milestone year draws to a close, here’s a review:

27 August: First Chandrayaan-3 science — temperature profile of the lunar soil

The “ChaSTE” payload on board the Vikram lander, whose job was to determine the temperature profile of the lunar topsoil, provided the first such profile for the lunar south pole.

ChaSTE, short for Chandra's Surface Thermophysical Experiment, was there to help us understand the thermal behaviour — relating to heat — of the Moon's surface.

ISRO represented the first data picked up by this instrument as a graph. The two parameters plotted are temperature and depth.

The graph told us how temperature varies with depth on the lunar surface and sub-surface, with measurements made a small distance beneath the lunar surface of the until-then unexplored south pole region.

For measurements below the surface, a temperature probe drilled down into the lunar surface and recorded the temperature.

For this purpose, ChaSTE had a temperature probe equipped with a controlled penetration mechanism capable of reaching a depth of 10 cm beneath the surface. The probe had 10 individual temperature sensors attached to it.

The graph showed that just above the lunar surface, the temperature is as high as 50 degrees Celsius. But a little beneath the surface, a little over 8 cm under, the temperature is about -10 degrees Celsius.

That's a difference of about 60 degrees Celsius over a roughly 9-10-cm distance in the lunar topsoil.

ISRO scientist B H Darukesha had expressed surprise at the "interesting" finding to news agency PTI: "We all believed that the temperature could be somewhere around 20-degree centigrade to 30-degree centigrade on the surface but it is 70-degree centigrade. This is surprisingly higher than what we had expected."

The wide variation in temperature above and below the lunar surface suggests that the "lunar regolith", the Moon's soil, is an excellent insulator.

The monthly summary of the Department of Space for September 2023 said as much: "The observed soil temperature... indicates the low thermal conductivity of the lunar regolith."

"This could mean it could be used to build space colonies to keep heat and cold and radiation out. This would make it a natural insulator for habitat," Mila Mitra, a former NASA scientist and co-founder of Delhi-based space education company Stem and Space, told the BBC's Geeta Pandey.

28 August: Sulphur presence confirmed ‘unambiguously’

A day after the findings from a Vikram lander payload were shared with the public, ISRO put out a result from a Pragyan rover payload called “LIBS.”

Short for Laser-Induced Breakdown Spectroscope, LIBS had "unambiguously" confirmed the presence of sulphur in the lunar surface near the south pole.

This unambiguous confirmation was not possible to achieve using instruments on orbiters.

In addition to sulphur, LIBS expectedly detected aluminium, calcium, iron, chromium, titanium, manganese, silicon, and oxygen.

“Thorough investigation regarding the presence of Hydrogen is underway,” ISRO had said.

Notably, these ‘elemental’ findings were part of the first-ever in-situ measurements of the elemental composition of the lunar surface near the south pole.

"Sulphur is a volatile element if it's not inside a mineral. So, if it's not part of a crystal, it's very cool to see it measured on the surface," Noah Petro, a project scientist at NASA, told the BBC's Soutik Biswas.

The sulphur find especially inspires confidence in lunar exploration and habitation by humans someday.

In a 1992 paper titled 'Uses of Lunar Sulfur', Los Alamos National Laboratory scientists had said, "Sulfur deserves serious consideration as a lunar resource."

"Sulfur in soils near the Moon’s poles might help astronauts live off the land one day, making these measurements an example of science that enables exploration," Jeffrey Gillis-Davis, a physicist at Washington University in St Louis, wrote in The Conversation, a leading publisher of research-based news and analysis.

According to Gillis-Davis, astronauts could use sulphur to build solar cells and batteries and make sulphur-based concrete — considered better in some respects than the one typically used — for construction, among other things.

30 August: Presence of sulphur and other elements reconfirmed with another instrument

After previously using LIBS, ISRO employed the other rover payload, the Alpha Particle X-ray Spectroscope (APXS), to once again confirm the presence of sulphur in the Moon’s south pole region.

"This finding by Ch-3 compels scientists to develop fresh explanations for the source of Sulphur (S) in the area: intrinsic?, volcanic?, meteoritic?," ISRO teased in an X post.

Besides sulphur, the APXS on board the Pragyan rover detected other elements like aluminium, silicon, calcium, and iron.

This finding was part of ISRO’s big task for the rover and its payloads to determine how different the elemental composition of the lunar soil and rocks is compared to that in other highland regions of the Moon.

APXS is said to be well-suited to carry out an analysis of the elemental composition of soil and rocks on the surface of planetary bodies with little atmosphere, such as the Moon. The APXS operation was caught on film.

31 August: Langmuir probe measures near-surface plasma content

The plasma near the surface of the Moon is relatively sparse, ISRO found after an initial assessment of data from the RAMBHA-LP payload on board the Vikram lander.

RAMBHA-LP is short for Radio Anatomy of Moon Bound Hypersensitive Ionosphere and Atmosphere–Langmuir Probe.

The Langmuir probe is named after the Nobel-prize-winning chemist Irving Langmuir, who invented the device.

The probe on Chandrayaan-3 was tasked with estimating plasma density and its variations.

Plasma consists of freely moving ions and free electrons. Regarded as the "fourth state of matter," it comprises over 99 per cent of the visible universe.

As part of Chandrayaan-3, RAMBHA-LP made the first-ever measurements of the near-surface lunar plasma environment over the south polar region.

As per the initial assessment of data taken early in the lunar daytime, the plasma at the lunar surface was characterised by a number density ranging from about 5 to 30 million electrons per cubic metre.

That the plasma was found to be "relatively sparse" is good news; the implication is that radio communication won't be disturbed a great deal on the Moon.

"These quantitative measurements potentially assist in mitigating the noise that Lunar plasma introduces into radio wave communication," ISRO said, adding that the data "could contribute to the enhanced designs for upcoming lunar visitors."

31 August: Seismometre on lander picks up a moonquake?

The Instrument for Lunar Seismic Activity (ILSA), a probe on board the Vikram lander, recorded the movements of Pragyan and its payloads as the rover navigated the lunar surface.

Constituting a cluster of six high-sensitivity accelerometres, ILSA was tasked with measuring ground vibrations generated by natural quakes, impacts, and artificial events.

On this day, ISRO shared data of the vibrations recorded during the rover's movements on 25 August. But, surprisingly, an apparently 'natural event' was also picked up.

"Additionally, it (ILSA) has recorded an event, appearing to be a natural one, on August 26, 2023. The source of this event is under investigation," ISRO said in an X post.

The 'natural event' is suspected to have been a moonquake. If that is the case, it would count as the first moonquake detection in decades.

Between 1969 and 1977, the Apollo lunar missions made the first detections of seismic activity on the Moon. Those findings indicated that the Moon possesses a complex geological structure beneath its surface.

Over the years, thanks to computer modelling and other analyses, a clearer picture of the Moon's interior has emerged.

ILSA was the first micro-electro-mechanical systems (MEMS) technology-based instrument deployed on the Moon.

27 October: Vikram lander’s ‘ejecta halo’ measured

After Vikram’s touchdown, a significant amount of lunar surface material was ejected, creating a bright irregular patch known as an 'ejecta halo'.

By comparing high-resolution images taken hours apart by the Orbiter High-Resolution Camera (OHRC) on Chandrayaan-2 before and after the landing, ISRO was able to characterise this ejecta halo.

The findings were presented in a study published on 26 October in the Journal of the Indian Society of Remote Sensing, authored by scientists from ISRO's Hyderabad-based National Remote Sensing Centre.

ISRO determined that approximately 108.4 m² of lunar surface was covered by the displaced ejecta, and estimated that around 2.06 tonnes of lunar material were ejected during the landing.

ISRO honoured

Apart from the frequent shower of praise bestowed on the space agency globally for months, ISRO received a particular appreciation for its Chandrayaan-3 mission just in time for the new year.

The Exploration Museum in Iceland's Húsavík recently awarded ISRO the Leif Erikson Lunar Prize 2023 for its "indomitable spirit in advancing lunar exploration & contributing to understanding celestial mysteries," the Embassy of India in Reykjavik, Iceland, said in an X post.

Ambassador Balasubramanian Shyam received the prize on ISRO's behalf, with ISRO Chairman S Somanath sending in a thank-you message.

May ISRO attain greater heights in 2024!

Relive the Chandrayaan-3 journey through the dedicated Swarajya dashboard.