Science from the Chandrayaan series by Ms. Megala.S

Added: 2026-05-21

[00:00:01]Good evening.

[00:00:03]Thanks to IIRS team for the opportunity.

[00:00:05]I'll be presenting the science outcome of Chandrayaan missions.

[00:00:11]This is going to be an interesting 1 hour because we are going to talk about the significance of the moon, the current trends, what is happening in the renewed lunar exploration scenario, and also the contribution from our country, that is the Chandrayaan missions and the science outcome of it.

[00:00:34]Let me start off by saying the significance of moon.

[00:00:38]The moon is a most fascinating object in the night sky, scientifically, aesthetically, and emotionally.

[00:00:45]The view of a full moon in the night sky is considered as an eternal beauty, and we all know it is beyond description of words.

[00:00:54]We can very well say that the life on the Earth is incomplete without the presence of moon in the night sky.

[00:01:02]But when you look at the inner solar system consisting of four rocky planets, Mercury and Venus do not have any satellites, and Mars has two tiny satellites, Phobos and Deimos, which are transient and happen to be there by chance.

[00:01:18]They are the bodies which is right to say that they might have roamed around the Martian orbit, and Martian gravity would have acquired them.

[00:01:28]That means that they were not there in the remote past of Mars, and they will be lost in the far future. It is that was strange that among the inner solar system objects, the Earth has a moon, that is a big moon, which is permanently going around the Earth, and it is there from the very beginning.

[00:01:52]We all know that the moon is massive when compared to all other things in the solar system. So, as the mass of the moon is substantial when compared to that of Earth, the Earth and Moon might have contributed mutually to the relative motion.

[00:02:10]In science, we call it as two-body problem where both the entities have substantial contributions to their collective dynamics. For the Earth-Moon system, this has given a major effects such as First of all, the moon is believed to have gravitationally stabilized the orbit of Earth with respect to the wobble, which was substantial to the initial years of formation.

[00:02:36]Thus, Moon's gravitational influence has facilitated an equitable climate on Earth.

[00:02:43]If you assume if the wobble of Earth has not subsided because of the gravitational effect of the moon, Earth would have experienced extreme temperature conditions.

[00:02:55]Secondly, in addition to this, tidal effects due to the gravitation of the moon has reduced the spin of the Earth.

[00:03:03]Uh it was initially very fast about 2 to 5 hours to the present 24 hours period.

[00:03:10]Imagine what would have been the state of our biological clock and circadian rhythm if we have such a fast-moving Earth.

[00:03:20]Thirdly, it is believed that it was lunar tides that brought marine life from seas because we all believe that the life originated in water. It's because of the tidal effect of moon, the life marine life which originated in the water migrated to land, and that's why we have become land-born species.

[00:03:45]The When you look at the birth of the moon or the origin of the moon, we all know that the giant impact theory is a most accepted hypothesis which it tells us that because of the giant impact of a Mars-sized body on the proto-Earth, the moon was born.

[00:04:04]And the moon was born because of a molten plasma.

[00:04:09]And after that, the plasma cooled down considerably. Solidification of magma happened and then the Earth becomes a differentiated body. What do you mean by the moon as a differentiated body is that the moon has a crust, mantle, and core up and so on.

[00:04:27]Till now, as it told by the scientist, there is a major events which formed as a geochronology of the moon. These are first, we consider the formation of solar system 4.5 billion years ago. Then the giant impact would have happened which it led to the formation of proto-moon.

[00:04:49]And that proto-moon has experienced a magma ocean. Then solidification happened. Then that time impact were huge number, so a lot of impact craters were there on the moon.

[00:05:02]With late heavy bombardment as resulted in young lunar basins in the lunar surface.

[00:05:08]After that, it was dominated by mare volcanism and the common and meteoritic impacts are happening even now. So, when you look at the moon, we could say that it is a natural laboratory to study the solar system. Which means that you study the moon, you understand Earth. You study the Earth, you understand the inner solar system.

[00:05:31]And the moon, since because it is a airless body, it has not undergone any chemical weathering. It is as it is, a record keeper.

[00:05:40]And the moon doesn't have a global magnetic field. That means that you get the solar forcing at 1 AU to understand the evolution of the moon, which is at a similar distance of Earth.

[00:05:55]And this moon provides a good reference for comparative planetology. And all the more for exploration point of view, what is more important is it is very easy to access. And moon is just few lakh km away, and it can be accessed by human in the form of orbiter, lander, rover, sample return missions, and also human missions.

[00:06:22]So, we have been studying the moon for long. But what are the current trends in lunar exploration is that now we are feeling that instead of just understanding the moon, we are trying to make use of the moon. That means from scientific understanding to looking at it at a point of view of resource potential.

[00:06:43]Then when compared to the short short-term exploration, which happens like few hours on the moon or few days on the moon, we are trying to utilize the moon to have a sustained human exploration, and to grab the resources in the lunar south polar region.

[00:07:02]The international cooperation is a very essential for exploration of such a grand endeavor because it has a difficulty of high risk and high cost.

[00:07:13]So, this lunar exploration is slowly becoming a global endeavor.

[00:07:20]When compared to the scientific understanding of the moon, moon could be used for many ways because moon is versatile. It can be used as a RF free radio observatory in the far side.

[00:07:33]Lunar habitats can be built there. Moon could be used as a space station to observe the Earth. It could be a launch base because moon has 1/6 of the gravity when compared to the earth. So, anything launched from the moon will have to undergo less escape velocity. And the scientific bases or research laboratory could be built on the moon.

[00:07:57]Now, having seen the significance of moon, when you look at the Indian lunar exploration roadmap, we all know the roadmap starts from Chandrayaan-1.

[00:08:09]But, the discussion to have a mission to the moon started in 1999 when a group of scientists, both from ISRO and non-ISRO institutions, such as research laboratories and universities across the country, came together. And at that point, ISRO was very well versed with the launch vehicle technology, spacecraft technology, and it was already demonstrated missions for remote sensing and communication. So, it was a right time ISRO was ready to take up such a master technology in and a challenging field that is the planetary exploration.

[00:08:45]So, unanimously the scientists came forward and told that yes, India should go to the moon. So, with that idea, the scientists and ISRO people started working together, which resulted in the launch of Chandrayaan-1 mission in the year 2008.

[00:09:03]Chandrayaan-1 is a mission which is having an orbiter and also an impact probe.

[00:09:09]After that, the little more than a decade, a comprehensive follow-on mission Chandrayaan-2 was conceived, and it was launched in 2019. And this has an orbiter and lander rover configuration.

[00:09:24]Though the landing attempt what was not successful, the orbiter, instead of having a nominal life of 1 year, it is now still in orbit, continuously giving the science data, and it is almost continuing for 7 years of time.

[00:09:42]In order to demonstrate the landing and roving capabilities, the Chandrayaan-3 mission was conceived, and it was launched in 2023. We all know it has a lander and a rover along with the propulsion module. So, when you look at the gradual progression of Indian lunar exploration roadmap, it is basically science-driven and goes with logical next steps.

[00:10:09]While doing the lunar exploration, we demonstrate a lot of technologies on the moon, and we expect that the lunar science community to be getting involved in all the missions of Chandrayaan series.

[00:10:23]By doing so, in the future, there will be a lunar sample return mission, Chandrayaan-4, followed by a south polar lander and rover to do in situ sample analysis, which is the Chandrayaan-5 or LuPEx mission.

[00:10:40]And when you look at beyond Chandrayaan-5, we do have a plan to go for a bigger lander and rover, a lunar navigation and communication architecture around the moon, a mission which will do in situ resource utilization. There will be definitely a crewed orbiter, and then which results in realizing the vision 2040, that is to put an Indian on the moon by 2040 and bring him back safely to Earth.

[00:11:11]The vision of Indian lunar exploration doesn't end there.

[00:11:15]After putting the humans on the lunar surface, there will be attempts made to build a scientific base on the moon.

[00:11:23]While doing so, the lunar exploration roadmap is in a full-fledged manner. We intend to do transformational lunar science with Indian lunar exploration program.

[00:11:39]Now coming to the first Indian mission to the moon, which is the Chandrayaan-1 mission.

[00:11:46]As I said earlier, the mission was launched on 22nd October 2008 by PSLV C11 launch vehicle.

[00:11:54]The mission is an indigenous mission with significant international participation.

[00:12:01]The high objective of Chandrayaan-1 is to do high-resolution remote sensing of the moon in visible, NIR, low-energy, and high-energy x-ray region to make a three-dimensional atlas of the moon, mineralogical and chemical mapping of the lunar surface.

[00:12:21]When you look at the mission configuration, it is very interesting because it had five Indian payloads and the moon impact probe along with six international payloads. Out of six, two has significant Indian collaboration.

[00:12:38]This mission worked for about 10 months and by 30th August 2009, the mission has concluded. But the 10 months of data was so unique that it even now there are publications coming out of this data. And the even now there is around 250 plus publications based on Chandrayaan data.

[00:13:02]When you look at the images which I have kept in the slide, the left side images are the pictures as I said about the moon impact probe which was intentionally made to crash land around the Shackleton region. And the moon impact happened at 89.8 degrees south, which is the rim of the Shackleton crater. And these are the images of the lunar surface was taken by the camera attached in the MIP >> [music] >> Moon Impact Probe.

[00:13:36]So, when you talk about Chandrayaan-1, the first thing which comes to the mind is discovery of water.

[00:13:44]So, when you look at the history of discovering of water, we all know that moon is extensively studied since 1960s by a number of flybys, orbiters, landers, rovers, and even human.

[00:14:00]But, Chandrayaan-1 holds the credit of discovery of water.

[00:14:04]Let us see the significance of it, significance of the scientific finding.

[00:14:09]So, water, be it hydroxyl, that is OH, or water, H2O, or water ice, or in any physical form, is an important resource on the moon, not only for establishing human bases, but also for understanding how volatiles behave and adapt water on the moon.

[00:14:30]So, if you assume the water can be expected on the moon because it could be endogenic of origin, that means when moon was formed, water was already there.

[00:14:43]That is the material which formed the moon might have got water in it. It is called endogenic water.

[00:14:50]And then, other one is the exogenic water. That means the water might have got deposited on the moon by impacting asteroids and comets over the ages. We all know comets bring lot of hydroxyl.

[00:15:04]And third reason could be in situ.

[00:15:06]Because the solar wind hydrogen, we have lunar silicates on the surface, plenty of O2, and they might have formed H2O water by chemical reactions.

[00:15:18]So, these three looks like the most possible cases for producing or generating water on the moon.

[00:15:26]In spite of these agreeable possibilities, the Apollo and Luna samples representing nine locations on the like near side of the moon did not contain any water or even the water of crystallization.

[00:15:41]So scientists thought, "Okay, moon is bone dry."

[00:15:44]But then when you look at the history of lunar exploration, there were sudden surge and number of missions in 1960s and 70s. But then they found that there's no water on the moon with a harsh environment. In 1980s, there is a lull in lunar exploration. There were no missions at all in the year 1980s as far as lunar exploration is concerned.

[00:16:10]Then comes two important missions, Clementine and Lunar Prospector.

[00:16:15]So they showed a trace evidence of could be water on the moon.

[00:16:21]So the most compelling evidence is that the lunar neutron spectrometer it indicated a significant decrease in epithermal to fast neutron ratio at the polar region.

[00:16:32]So we all know how the moon gets fast neutrons. These are produced by cosmic ray interactions with the elements present within the upper meter of the lunar surface such as iron, oxygen, aluminum, etc. And they get thermalized by the hydrogen if it is present there.

[00:16:51]So the epithermal to fast neutron ratio should therefore decrease in the presence of hydrogen bearing compounds.

[00:16:58]So the Lunar Prospector data indicates that about 1 billion tons, just imagine, 1 billion tons of water is present in the lunar poles.

[00:17:09]So the best fit fit model what they have done on the ground indicates that in the deeper depths such a lunar neutron spectrometer is not very effective. And scientists also told that the mere implantation of hydrogen on the lunar surface is also considered as water in the case of neutron prospector.

[00:17:31]So, the evidence is not conclusive.

[00:17:36]Another evidence for the presence of water is given by the bistatic radar experiment carried out on Clementine.

[00:17:43]So, based on the polarization of the reflector to incident signal, the possibility of water to the lunar south pole is shown.

[00:17:51]So, a supporting evidence came from the observation made during the passage of the spacecraft near the south pole, but it detected a positive signal for the presence of lunar water.

[00:18:03]But, when you look at the same signal from ground, for example, the Arecibo Observatory, it was not showing any signal of water.

[00:18:13]Whereas, when you look at the case of Mercury, both in the bistatic radar and also in the ground, they have seen water ice in the polar regions of Mercury, but it is not coming out in the case of moon. So, there was a confusion whether at all there is water in the south polar region.

[00:18:32]The water molecule released from the lunar surface undergoes a ballistic trajectory depending upon the thermal energy, and it hops from place to place until it finds a permanent cold trap, which is the permanently shadowed region both in the lunar north and south polar region. So, till 1996, it was inconclusive that there is a presence of water on the moon. Now, having set that background, now we will look at the Chandrayaan-1 data.

[00:19:04]So, the left side image, the leftmost image indicates the outcome from the moon mineralogy mapper. So, this is an IR sensor which could measure the reflex 10 spectrum between 0.4 to 3 micron wavelength range.

[00:19:20]In the spectra taken near the lunar poles, you could see the blue color here. In the lunar poles, the instrument showed prominent absorption bands from 2.8 to 3 microns corresponding to OH or H2O.

[00:19:36]But these bands are negligibly small in the equatorial regions.

[00:19:41]So, the production of these ions is attributed to the reduction of lunar silicates containing oxygen by solar wind hydrogen.

[00:19:50]The next image is the image from the synthetic aperture radar which is a mini SAR working in the S band 2.54 GHz which could penetrate the subsurface regions up to a top few meters.

[00:20:06]So, working in active mode, it was designed to transmit circularly polarized signal and receive the scattered signal from the lunar surface.

[00:20:15]The sense of reflected polarized signal and its ratio with respect to the incident signal which we in science we call it circular polarization ratio, depends upon the dielectric constant of the scattering material.

[00:20:29]But the roughness of the moon surface, that is fresh craters, also influences CPR and can mimic water ice which is not true.

[00:20:38]So, what we did in mini SAR is we have located the fresh craters using TMC images both in the north and south polar region and we have removed them visually.

[00:20:50]So, there were craters old enough to hold water ice and it was visible from the mini SAR spectra.

[00:20:57]So, these are the potential regions where water ice deposits are available in both the polar regions. However, the number decreased when it moved towards the equatorial region.

[00:21:10]The third image is the chase, which is a mass spectrometer on the moon impact probe.

[00:21:18]Beyond two on the on November 14th November 2008 the moon impact probe separated from the Chandrayaan-1 when the orbiter was at an altitude of 100 km and it descended towards the lunar surface.

[00:21:34]It took nearly 3,000 pictures of moon surface and 650 mass spectra of lunar atmospheric constituents during the lunar day.

[00:21:43]The mass spectra revealed the atomic mass unit AMU 18, 44 and several other minute constituents. And this AMU 18 corresponds to water molecule. And this got dominated when it moves towards the polar region. So, direct evidence of water in the lunar exosphere was established with this measurement. So, now when you look at the outcome of Chandrayaan-1, we have seen water or hydration on the surface using M3, on the subsurface using Mini-SAR, and also on the exosphere using the chase on board moon impact probe. Thus, without any ambiguity, water signatures were detected by Chandrayaan-1 and bags the discovery to its credit.

[00:22:36]And it is not only water, there are several interesting results from Chandrayaan-1.

[00:22:41]A significant result was obtained by the swim, which is the solar wind monitor on board the SARA experiment payload, which had the capability of directional measurement of hydrogen ions. You could see here swim, solar wind monitor.

[00:23:01]It measured the solar wind hydrogen impinging on the moon and those which are released by the lunar surface back into the lunar environment. This left side image was telling the same thing.

[00:23:14]The measurement indicated that the number of hydrogen ions released by the lunar surface is over 20% of incident hydrogen ions.

[00:23:24]This is unexpectedly too large because the initial thought it was whatever the hydrogen atoms which are impinging on the lunar surface will be reflected back to the lunar surface as energetic neutral atoms. But contrary, we found in SARAH experiment that 20% of the of the hydrogen atoms are reflected back. And Kaguya experiment on the onboard Kaguya mission found that about 0.1 to 1% of solar wind ions are reflected or scattered back by lunar surface grains. But this has given a new dimension to the solar wind and lunar surface interaction.

[00:24:14]Another important result is the about the lunar volcanism.

[00:24:19]There's an example which is a Tycho crater. It's one of the most prominent crater on the moon because it appears as a bright spot in the southern highlands with a race of bright material that stretch across much of the near side.

[00:24:36]The Tycho, when you look at it, it is not uh due to the size, but it is one among the thousand craters. But what makes Tycho really important is its relatively youth when compared to the surrounding areas on the moon.

[00:24:53]It formed recently enough that its beautiful rays material ejected during the impact event are still visible as bright streaks. All craters start out looking like this after they form, but their rays gradually fade away as they sit on the surface exposed to space environment, which over time darkens until they fade into the background.

[00:25:18]The age of Tycho is estimated to be 110 million years.

[00:25:24]Though it seems to be a longer time when compared to the moon formation dating back to 4.5 billion years, this is relatively young. So, using TMC 2, that is current mapping camera, and LRO images, scientists saw the lava ponds, which you can see here, lava ponds, and then vents, and then fractures, and then flow of lava.

[00:25:49]This indicates that moon is not geologically dead as we once thought. It is relatively it is still active.

[00:25:59]When we talked about the birth of the moon or the origin of the moon, we were telling about the giant impact hypothesis. And I was telling you that the moon was once molten fully, and then it got solidified. So, the basic process involved that the magma ocean when when it's getting cooled, then differentiation took place, which means that heavier minerals, such as iron, titanium, sank to the bottom, and lighter minerals composing of aluminum, calcium, and silicon floated to form the crust of the moon. So, the heavier minerals, which are constituted by iron and titanium, went inside, and lighter minerals came outside.

[00:26:43]So, this in the left side image, I'm showing a hypercube of an Oriental Basin.

[00:26:49]And the markings 1 2 3 4 are the four regions which are given in the reflectance spectra in the right side.

[00:26:57]That in the M3 spectra I could clearly see that anorthosites composing aluminum calcium silicates are on the top and then the other things like pyroxene features are in the bottom. But, this means that the global magma ocean hypothesis, that is the moon was formed after the giant impact and there was magma ocean is validated.

[00:27:27]But, now very much we talk about being the current trends of the lunar exploration about sustained human presence on the lunar surface. But, when you look at it, moon is very harsh, doesn't have an atmosphere or a global magnetic field, and all the sun rays are falling straight on the moon. So, it is a harsh environment for a human to survive there. So, do we have any place on the moon that we can build a habitat or a built a potential site where human beings can rely on? Yes, there is such a site which was found by DMC.

[00:28:07]The lunar surface, as we know, it is exposed to levels of hazardous radiation, which is 150 times greater than that on Earth.

[00:28:16]And it's fully vulnerable to deadly coronal mass ejections from the sun, as well as perpetual rain of impacting meteorites. And the extreme temperature between the day and night is also very much harsh.

[00:28:30]So, these are the few regions that show a hope for providing safe shelter for the human explorers of the moon, such as volcanic lava tubes, which are free from the hostile effects.

[00:28:43]These may be adequate for human settlement, which is an important perspective of long-term research and development in outer space.

[00:28:52]Lava tubes are formed when an active low viscosity, that means a lesser dense lava flow happens, a continuous hard crust due to continuous cooling of this uppermost part, which thickens with time. And forms a solid roof above the still flowing lava beneath.

[00:29:13]Often, if the uh if the conditions are conducive, an empty flow channel free from molten magma is left behind in the form of cylindrical shaped tube called the volcanic tube.

[00:29:26]So, the TMC on board Chandrayaan-1 has detected a buried, uncollapsed, near horizontal lava tube as shown in this picture.

[00:29:36]This could be in future characterized and could be used as a habitat for human beings.

[00:29:44]The next important mission is the comprehensive follow-on mission when compared to Chandrayaan-1 is the Chandrayaan-2 mission.

[00:29:54]So, this is the second lunar mission taken by ISRO, and it is a complex and very challenging mission undertaken.

[00:30:03]It was launched on 22nd July 2019 by GSLV Mark III from SHAR. It was inserted into lunar orbit on 20th August and achieved 100 km orbit on 2nd September.

[00:30:17]As I said earlier, this was designed to be an orbiter, which will work for 1 year.

[00:30:24]However, it is completed 7 years in orbit and continue to do so by providing important data.

[00:30:33]The scientific objective of Chandrayaan-2 mission is to expand the lunar scientific knowledge through detailed study of topography, mineralogy, surface chemical composition, thermophysical characteristics, and tenuous lunar atmosphere leading to better understanding of origin and evolution of the moon.

[00:30:53]When you look at the eight state-of-the-art payloads on board the orbiter, there are two cameras.

[00:30:59]One is the high resolution camera. Other one is a terrain mapping camera, which is a follow-on of TMC one of Chandrayaan-1.

[00:31:07]The For understanding the elemental composition of the lunar surface, we have class experiment. And the input is a solar flux, which is monitored by the solar x-ray monitor.

[00:31:21]To map the minerals and to look for unambiguous water ice detection, the in imaging infrared spectrometer was on board, which will map the minerals in 0.8 to 5 micron range.

[00:31:37]The dual frequency synthetic aperture radar is one level level above the mini SAR experiment, which can look at the polar regions for water ice in L and S band mode.

[00:31:49]The CHACE-2 experiment is a follow-on of CHACE-1 experiment to study the neutral species in exosphere and its spatial and temporal variation. And there is a dual frequency radio science experiment to study the neutral environment of moon.

[00:32:07]So, when you look at the scientific findings from Chandrayaan-2, the first one is the orbiter high resolution camera. And the unique aspect is that this camera can give you imagery of 25 to 32 cm resolution. You just imagine if you are at 100 km orbit around the moon and you could see the craters which are less than 5 m diameter and a boulder which are 1 to 2 m height. Such a sharpest eye, the lunar orbital platform, is a uniqueness of this over chassis payload. The imagery plays an important role in the landing site characterization both for Indian as well as international missions.

[00:32:55]In the earlier case of Chandrayaan-1, we told that the moon mineralogy mapper has the wavelength range of up to 3 micron.

[00:33:05]But, when you look at the water ice signature, it comes around 3.2 microns.

[00:33:10]So, in order to have a complete picture of what is happening between 3 to 5 micron region, we have imaging IR spectrometer on board.

[00:33:21]And when you look at the result which is kept on the top, it has indicated that water in various surface types and latitudes. This means that water is not only restricting itself to the polar regions, but it is also widespread across the equatorial regions, but concentration may vary.

[00:33:41]As a total water concentration, it varies between 0 to 800 ppm, and it has a control on the mineralogy and the latitude of the existence.

[00:33:52]The right side image shows the hydration features of Shackleton crater in the lunar south pole. And it was found that about 700 to 1,400 ppm water is available in the Shackleton crater.

[00:34:09]One of the main outcome of this class payload, which is the uh which is meant for elemental composition studies, is to understand the origin and evolution history of the moon.

[00:34:25]And one of the direct ways to determine the surface elemental abundance is the X-ray fluorescence spectroscopy. The CLASS payload mapped the sodium, potassium, phosphorus, chromium, and manganese, which are considered as minor elements of the lunar surface with abundances less than 1 weight percentage.

[00:34:46]As the solar cycle is in ascending phase, CLASS continues to operate measuring X-ray spectra leading to global high resolution elemental maps.

[00:34:56]Shown here is a magnesium aluminum elemental map from the CLASS payload.

[00:35:05]When we talk about the moon mineralogy, when you talk about the dual frequency synthetic aperture radar, as I mentioned, it can work in two bands. One is the S-band, and other one is the L-band, which can dive little deeper into the subsurface.

[00:35:22]Shown here is a comparison image of a DF SAR, that is the left side image, as compared to the optical image of LRO.

[00:35:31]What is interesting to see that many craters such as 1 2 3 is all optically covered, that means in the optical images, some of the characteristic features of craters will not be visible. So, we need a dual frequency synthetic aperture radar to understand the kind of impact happened on the lunar surface along with how much disturbances it has done on the lunar surface.

[00:36:04]The DF SAR payload has given new insights on the Peary crater, which is a 78 Here, this is the crater.

[00:36:13]This Peary crater 78 km dia in the lunar north polar region. It is viewed by the L-band SAR.

[00:36:22]So, the L-band SAR is giving hint that there could be water ice in the lunar north polar region of exploitable depths.

[00:36:32]So, when we go on looking at the lunar surface for over the period of years, we will get a complete circular polarization ratio CPR map of both north pole and the south pole. So, this is the north pole and this is south pole and this is the data of CPR well taken from the DFR payload.

[00:36:54]So, the above data products based on L and S bands are which is the CPR maps on the combination of several parameters such as the surface roughness, density, porosity of the lunar surface, potential presence of water ice, etc. So, this kind of ready-to-use products on the lunar regions will provide holistic information to characterize the polar regions for future lunar exploration. So, these products complement hyper-spectral data in studying the distribution of minerals on the moon and this data is already released to public through PRADAN website.

[00:37:35]So, shown here is the global observation of CHASE 2 of Argon 40.

[00:37:41]So, Argon 40 is one of the isotopes of noble gas Argon and is an important constituent of the lunar exosphere.

[00:37:49]It originates from the radioactive disintegration of 40K, that is potassium 40, which has a half-life of about 1.2 into 10 ^ 9 years.

[00:38:02]The radioactive 40K nuclide, which is present deep down the lunar surface, disintegrates to Argon, which in turn diffuses through the space and makes its way up to the lunar exploration through seepages and falls in the lunar surface.

[00:38:19]In the lunar exosphere from an altitude of around 100 km, it this payload captured the day night variations of the concentration of argon 40.

[00:38:31]After the lunar dawn, the argon 40 start getting released to the lunar exosphere.

[00:38:38]Understanding the global dynamics of argon using CHACE-2 data is an important result from the Chandrayaan-2 mission.

[00:38:48]Now, when we look at the Chandrayaan-3 mission, to give an overview, the biggest launch vehicle of ISRO, LVM3, launched Chandrayaan-3 integrated module on July 14, 2023.

[00:39:02]After several orbital maneuvers, the lander and rover soft landed on 23rd August 2023.

[00:39:11]The spacecraft comprises of three modules. First one, the propulsion module, and then the landing module, which has a rover within it.

[00:39:24]So, this is a mission profile, which it shows that as an integrated module, the Chandrayaan-3 was launched, it underwent several earthbound maneuvers, and then it is putting into lunar transfer trajectory, and further it got captured by the moon, and then it has become the 100 into 30 km orbit.

[00:39:45]Once the integrated module reaches the 100 into 30 km orbit around the moon, it got separated, and then the lander deboost happened, which resulted in the successful soft landing of Chandrayaan-3, Vikram.

[00:40:02]When you look at the payloads, the lander payloads are meant to study the ground vibrations, seismicity, thermophysical properties, and near surface plasma environment.

[00:40:14]The The payloads are meant to study the elemental composition of the regolith.

[00:40:19]And in the propulsion module, there is an experimental payload called SHAPE payload to observe the Earth as an exoplanet. And in the shown in the left are the real images wherein the seismometer is getting deployed. And then the ChaSTE, a thermal probe, getting inserted in the lunar surface.

[00:40:38]And deployment of a Langmuir probe, the shadow you could see on the lander.

[00:40:48]So, these are the images where the rover rolled out from the lander. And a crater which is encountered by the rover. And this is the path retraced. Or this you can say is the footprint of rover on the lunar surface. And the distance covered by the rover from the lander is approximately 101 m.

[00:41:11]So, as a mission Chandrayaan-3 has accomplished the original mission objectives. And also, it has extended mission accomplishment. Which are the demonstration of hopping by refiring the engines. And then the deorbiting the propulsion module from the lunar orbit to the Earth orbit.

[00:41:32]So, science-wise, all the payloads worked for one complete lunar day. And they have collected excellent quality of data. There were very good number of publications from Chandrayaan-3. And the data is already made open to public.

[00:41:47]So, the uniqueness or ingenuity of Chandrayaan-3 is in the landing itself.

[00:41:52]Because when you look at this map of Apollo, Luna, and Chang'e 3 Chang'e 3 and 5 landed in the near side. And Chang'e 6 landed in the far side of the moon. Which is not represented in this figure. And Chandrayaan-3 landing site is the one which is very closer to the lunar south polar region. And it is named as Shiv Shakti point.

[00:42:18]When you look at the science results from the Chandrayaan-3 mission, the first prominent one is the elemental composition of the Shiv Shakti region. The APXS are the alpha particle x-ray spectrometer on the rover conducted in situ measurements of elemental abundances in 23 locations around the landing site. And what is inferred is the regolith around the Shiv Shakti point is made up mixture of two rock types. One is ferroan anorthosite and the other one is the magnesium suit.

[00:42:52]So, this measurement also validates the lunar magma ocean hypothesis.

[00:42:56]The magnesium-rich minerals which are shows that some part of the mantle got excavated during the formation of south polar Aitken basin region, which got transported into the Shiv Shakti region.

[00:43:12]The same thing another result also proved that the spa basin, which is impacted by a huge impact, the material which came out of those impact has shifted to the Shiv Shakti region.

[00:43:32]And the reason why we are saying is that this experiment has found that the anomalously low levels of sodium and potassium, but higher levels of sulfur when compared to what was found in highland soil samples from Apollo 16 and Luna 20 mission indicates that the part of mantle material is available in the Shiv Shakti region.

[00:44:01]The seismometer.

[00:44:02]We all know that there are several types of moonquakes.

[00:44:06]Deep, shallow, thermal, and impacts due to meteorites. But, what is the origin of those impacts and what could be the cause of the same? And whether there are any measurement in the high latitudes, it is no. So, ILSA was operated for around 190 hours and identified more than 20 distinct signals, the amplitude ranging from 1 micro G to 5 milli G, varying from 1 second to 14 minutes.

[00:44:36]The large amplitude signals are those corresponding to rover navigation bearing, the dynamics of the rover and wheel-soil interaction is a source of complex ground vibration signal. The longest one The longest one occurs for about 40 14 minutes.

[00:44:54]So, there are several instances, around 50 of them, where the amplitude of the signal is different from the normal background signal. And these are called as uncolored events, and the signals spread over a wide range of 50 hertz and lasted for only few seconds. So, the recent paper, even from the Japanese colleagues, indicates that the signal levels of uncolored events are matching with lander resonances and payload activities, hence there could not be any natural origin.

[00:45:28]The other important result which came from Chandrayaan-3 is the way that the Chandrayaan-3 landing site is a buried impact crater.

[00:45:38]Yes.

[00:45:39]This semi-circular structure encompassed the Shiv Shakti point. This is here in the figure, star is a Shiv Shakti point.

[00:45:47]This reveals that these are the rims of the buried crater. So, it means that there was a crater earlier on the moon, which was buried, and over the top of that Chandrayaan-3 has landed. But, this shows that complex history of cratering which is happening throughout the geological history of the moon.

[00:46:09]The lunar surface and subsurface and the temperatures dictate a complex interplay of number of parameters. Based on earlier observations and modeling, the understanding is that the surface of the moon can be best represented in terms of two distinct thermal regions. A superficial porous layer which is top few centimeters we can say fluffy and the bottom which is about 1 m which is having a denser layer.

[00:46:40]So just Chandrayaan-3 is a thermal probe which got inserted in the lunar surface.

[00:46:45]And it found it has measured the temperature and also the thermophysical properties of top 10 cm of the lunar surface.

[00:46:54]The peak surface temperature was 355 K which is about 25 K higher than speculated.

[00:47:02]This means that the lunar surface temperature showed a significant spatial variability even at meter scales at higher latitudes unlike the equatorial regions which show in the meter scale there won't be any variations.

[00:47:16]This is an important result from the Chandrayaan-3 probe.

[00:47:21]And a recent finding is that the regolith heterogeneity of the moon's south pole. We all know that there was a hop experiment conducted. That is the Vikram lander soft landed in August and after that after after completing the experiment on September 2nd, the Chandrayaan-3 Vikram re-ignited its engines to perform a hop maneuver or a jumping maneuver. So after that hop is done, the thermal probe was again inserted into the lunar surface.

[00:47:55]That is on the lunar regolith. So, what we found is because of the lander plume exhaust, the top 3 cm loose dust was eroded in the secondary location. And because of the top surface eroded, the temperature measurement was only pertaining to a two-layered stratigraphy.

[00:48:18]It means that at a depth of 6.5 cm down, the soil is denser and behaves more cohesive in nature.

[00:48:27]And these observations were taken during the twilight time, that is 17:35 p.m. at the local time on the moon. That means that small objects on the moon cause a long shadows, which has created significant drop in the temperature profile. But these results, though at one-point measurements, are very crucial when you are thinking about constructing scientific bases on the moon.

[00:48:54]Another important result is about the near-surface plasma density.

[00:48:59]We all know that the moon is immersed in the solar wind plasma, where ions and electrons have variable speed. And due to the faster speed of the thermal electrons, the lunar surface would collect electrons and negative charge in the absence of other currents.

[00:49:15]And lunar plasma is one of the good example of a dusty plasma.

[00:49:20]So, the in situ measurements from the Langmuir probe indicated that the estimations reveal that daytime lunar plasma have a mean electron density, which is much greater than expected. And the energy of electrons is 3,000 to 8,000 K, indicates that the process of that impart high energy of electrons.

[00:49:45]And the contributions from the solar wind when the moon is outside the geomagnetic tail and Earth's magnetospheric particles when the moon is inside the geomagnetic tail has been inferred. So, both the elemental and molecular ions contribute to the moon's near surface plasma.

[00:50:05]So, when we talk about the missions accomplished, we should talk about the missions which are under development, right? So, there are two missions. The one is the Chandrayaan-4 mission, which is aimed as a lunar sample return mission.

[00:50:19]The mission objective is to bring back lunar samples back to Earth safely for connecting transformative scientific analysis.

[00:50:28]This is going to be a very, very challenging mission as the mission has two LVM3 launches. It will be having an ascender and descender module as a stack one, launch one, and transfer, re-entry, and propulsion module as stack two.

[00:50:44]What they envisage is that the two launches will happen and the spacecraft modules get integrated in the Earth orbit. After the jettisoning of propulsion module, all the four modules travel to the moon, and then the uh ascender and descender module will perform a powered descent and land on the designated lunar site in the southern high latitudes of the moon. Once the ascender landing module collects the samples and put it in the ascender module, it will ascend from the lunar surface and get docked to the transfer and re-entry module.

[00:51:28]Then, the re-entry module will come back to the Earth along with these pristine lunar samples collected from the southern high latitudes. So, the mission is going to be a very challenging one, and the potential landing site under study is around southern high latitudes, that is among small and region as we have ancient terrain and there's a possibility that we will get samples from these output at skin basin ejecta and that it could have PSR with indication of water ice. The mission is under development and it is targeted for 2028 time frame.

[00:52:07]So, the most important thing in Chandrayaan-4 mission is not just the mission, but the samples or the pristine lunar samples which we are going to collect from the moon. Uh this is going to be unique because the science enabled by return sample is very unique when compared to the remote sensing and in situ measurements. So, the much of the science is concentrated in analyzing the samples on ground. We may be having some cameras, sensors, or a spectrometers in the spacecraft modules, but useful insights depends upon the geologic interpretation of analyzed samples.

[00:52:47]So, this return samples will take advantage of all the instrumentation and capabilities available on the earth, not only which is available now, but also which will will be coming up in the future.

[00:53:00]So, there is a laid-out plan from how to recover the sample till analyzing the sample. It starts from screening the radiation photography and before and after the entry of re-entry module right from the environmental sampling till the documentation, the process is evolving.

[00:53:23]The mission which is going to have a scientific potential in future is the Chandrayaan-5 LuPex mission. It is a joint ISRO-JAXA joint mission to the lunar south pole.

[00:53:37]The objective of the mission is to measure the quantity and quality of water and other volatiles in the lunar south polar region and determine the regolith composition.

[00:53:49]We know from the Chandrayaan-1, Chandrayaan-2, and other missions data that water is present on the moon. But, what is the abundance of water? What's the distribution of water? Whether it can be usable is a big question mark. So, to understand the usability or the quantity and the quality, which means the physical form of water, we will be launching Chandrayaan-5 in the year 2028.

[00:54:18]And the uniqueness of the mission is that it is a long-duration mission. That means around 100 Earth days and this mission is going to be there on the moon. LUPEX is nothing but an in-situ laboratory in the lunar south polar region.

[00:54:34]It is a big rover of about 350 kg and which will also do an study of permanently shadowed region in the lunar south pole. When you look at the responsibility of both the agencies, ISRO will be developing the bigger lander, which is of 6.5 ton, and it will be landing on the moon and scientific payloads on the rover and the lander.

[00:54:58]The LUPEX rover or the sophisticated rover of about 350 kg is from the JAXA and launch will be from JAXA.

[00:55:07]Mission operations, science, investigations will be common to both sides. And as a mission, this has payloads from NASA and ESA as well.

[00:55:20]The unique set of payloads, which are around the scientific theme of Chandrayaan-5 is the four ISRO payloads on board the Chandrayaan-5 rover. The first one is a water scouting surface penetrating radar, which is nothing but a GPR, which has in a frequency of 0.5 to 2 GHz. And it can go up to the depth of 3 m to understand subsurface water ice presence in the lunar south polar region.

[00:55:51]Our second one is the mid-IR spectrometer. It is a hyper spectral imager similar to what we have in Chandrayaan-2, the imaging IR spectrometer. And it it intends to map the surface hydration and mineralogy.

[00:56:06]There's a PRATIMA probe which is a permittivity and thermophysical investigation for Moon's Aquatic Scout PRATIMA. It will detect regolith bound water ice using a technique of dielectric permittivity. And one another important payload is the Raman spectrometer which will be collecting, analyzing the in situ lunar samples. And this is called ISRO's Sample Analysis Package or ISAP. And objective is to estimate the mineralogy of the drilled sample and look for signatures of volatiles. The mission profile is that after landing, the rover will be coming out and the rover move to a region where the neutron spectrometer will be look for hydrogen flux, GPR will look for subsurface ice, and then the mid-IR spectrometer and the spectrometer from Japan will look for the surface hydration features. When everything goes positive, there's a drill in the rover which will drill the lunar surface and take a bit of sample.

[00:57:08]And one part of the sample will go to the Japanese instrument and other part of the sample will go to Raman spectrometer. For the sample which is collected by the JAXA instrument, will be heated so that the volatiles come out of it and there will be a gas analyzer to understand the composition of that.

[00:57:26]So, by measuring the composition of the volatiles, the amount of water present at the lunar surface will be estimated. So, this is going to be a 100 days duration mission and it is going to prove or validate the presence of water ice or water on the lunar south polar region. So, these are the interesting missions which are there.

[00:57:51]And I would say that the future of lunar exploration is very bright with the ISRO's vision telling the first Indian on the moon by 2040. I wish everybody listening to this to contribute and I welcome all of you to be part of the Indian lunar science and exploration missions. Thank you so much.