DR J.N. GOSWAMI, Principal Scientist, Chandrayaan-1 mission, and Director, Physical Research Laboratory (PRL), Ahmedabad, is extremely happy today. For, the Moon Mineralogy Mapper (M3), a payload of the NASA on board Chandrayaan-1, has detected the presence of water in moons soil. The High Energy X-ray Spectrometer (HEX), another Indian payload jointly built by the PRL and the ISRO Satellite Centre, Bangalore, looked for water ice in the polar regions of the moon and identified possible regions of thorium and uranium concentration.
The suave and articulate geoscientist was responsible for the collation and sharing of the data from all the 11 scientific payloads on Chandrayaan-1. He worked closely with NASA in analysing the findings of M3. In an e-mail interview, Goswami said he was confident that other important results will follow. Excerpts:
As the Principal Scientist of the Chandrayaan-1 mission, how do you characterise the entire scientific value of the mission in the light of its discovery of water molecules on the lunar surface?
Let me start with a bit of background. ISRO [Indian Space Research Organisation] could have just demonstrated its technological competence to explore our closest neighbour, the moon, with a few payloads for mapping the lunar terrains and its chemical/mineralogical composition. Ensuring successful lunar capture and placing a satellite in a designated lunar orbit in the very first attempt would have been a very significant achievement. However, a decision was taken that Chandrayaan-1 will be both a technology demonstrator and science mission that can stand out at the international level. Science goals and some instruments to be developed in-house were defined and, thanks to ISROs vision, we could also select instruments from foreign countries based on the proposals received following an Announcement of Opportunity.
This whole process made Chandrayaan-1 stand out as a remarkable science mission and a role model for international cooperation in planetary exploration. The detection of the signature of water molecules in the top layers of the lunar surface, which is a major breakthrough, speaks volumes about the scientific value of the mission. I am confident that other important results will follow.
You described it as a very, very important discovery in global science. You called it a global discovery, not merely a national discovery. How is it important globally?
This discovery is truly important in the global context, particularly, when one considers the renewed international effort for planetary exploration.
Scientifically, the very fact that the moon, which was considered bone-dry after the analysis of the Apollo and Luna samples, can host water molecules over a large part of its surface suggests that objects of the solar system with reasonable gravity and devoid of an atmosphere and a magnetic field can in principle host water molecules produced by solar wind interactions. Of course, the impact of comets and certain type of asteroids can also bring in water. The renewed interest and vigour shown in planetary exploration by various space agencies in the 21st century makes this discovery important in the global context. The hypothesis that water molecules may be present on the moon and their possible movement to colder polar region where they get trapped in areas permanently shaded from sunlight appears to be closer to reality now.
Chandrayaan-1 has provided the proof for the first part only; we have to wait for the completion of the analysis of data from Mini-SAR [Mini-Synthetic Aperture Radar from NASA], another instrument on board Chandrayaan-1, for the second aspect.
The presence of water and sunlight will not only provide local resources on the lunar surface for exploring the moon but increase the potential of harnessing the same for implementing ideas such as using the moon as the base for further exploration of the solar system. Of course, this is likely to happen only in the distant future, the first solid step for the same has been provided by Chandrayaan-1.
You were very critical of the discovery in the beginning, meaning you demanded exacting standards to prove that there were indeed water molecules. What kind of critical observations were NASA and you doing for the past three months to prove the discovery?
If you ask anybody who has worked with the lunar samples during the Apollo and Luna era I belong to that group it is difficult to think that hydroxyl [OH] or water [H2O] molecules may be present on the lunar surface except in very particular situation [permanently shadowed traps]. Even Carle Pieters, the Principal Investigator of M-cube [M3], who was also involved in Apollo missions, had a similar feeling. There were some reports during the Apollo era about the detection of water in returned lunar samples and these were generally attributed to terrestrial contaminations. So, it was important for us to ensure that the signal we have seen is beyond any doubt.
How we did this we thoroughly checked instrument calibrations, covered some sites repeatedly and others when the sun was shining at very different illumination angles [lunar mornings and afternoons], and in between also carried out a procedure for decontaminating the instrument as well, just to be sure. After two months we were sure the signature is for real.
We then did something not often done. We shared the information with the Deep Impact Mission team [one of the M-cube members is a senior scientist of that mission] and as the spacecraft was to swing by earth-moon system during early June 2009, we requested it to make some observations. This mission carried a similar instrument that covers the 1 to 4.5 micron range. It found the same signatures. The mission also relooked at archived data of the moon, collected in 2007, for instrument calibration and found that the signature was found there, too.
More interestingly, one of the M-cube team members, who was a co-investigator of the Cassini mission to Saturn that carried an instrument covering the 0.3 to 5 micron range and observed the moon in 1999, looked at the data and found tell-tale signatures of OH and H2O molecules.
So we decided to go ahead, the three teams submitted the papers to an international journal of repute [Science] and the papers went through the process of peer review and got published on September 24.
How did the mass spectrometer of the MIP detect the water molecules during its descent towards the moon? The MIP was forgotten after it crashed on the moon on November 14, 2008. Where did the MIP locate the water molecules on the lunar surface or in the permanently shadowed polar regions of the moon?
The MIP carried a mass spectrometer for possible detection of any molecule that it might encounter in the lunar environment [within 100 km, the orbit of Chandrayaan-1] after it was released, northward of the equator, and before it hit the lunar surface near the south pole. The data returned by the mass spectrometer indicated the presence of many molecules of different masses, including a signal at mass 18, which happens to be the atomic mass of water. Unfortunately, it was a one-shot experiment that could not be repeated for obvious reasons, unlike in the case of M-cube observations. If we attribute the signal at mass 18 to the water molecule, we must be able to identify all the other masses detected along with their plausible source.
We have also to ensure that we do not have any contaminants. The mass-spectrometer team has put in a lot of effort to achieve this goal and the results are discussed at the meetings of the Chandrayaan-1 Science Team that are scheduled periodically. However, to establish any new scientific finding, we have to remove all ambiguities, put it up for peer review and publish the same.
To sum up, we have some extremely interesting data from the mass spectrometer but we have to cross a few more steps before we can tell what it means with scientific certainty.
You said, We saw it first. But others also saw it. Was ISRO too careful not to reveal the discovery on its own soon after the MIPs discovery?
I think you have heard it wrong [if you were there at the press conference in Bangalore on September 25] or somebody quoted it wrongly. I do not exactly recall if Chairman, ISRO, may have said it. This is an issue I do not want to get into.
Compared with other instruments on Chandrayaan-1, how did the MIP perform? How significant is this success for India?
The success of the MIP stems from the fact that we could release it and make it land near the south pole as per plan. Two instruments on board the MIP [the camera and the mass spectrometer] worked perfectly and provided useful data. The photographs obtained by the camera allowed us to reconstruct the path of the MIP as it moved over the moon and also identify the landing site. The mass spectrometer yielded interesting data. I think in addition to the technical and scientific aspects, if you simply look at the popular reaction to the MIP impact on the moon on November 14, 2008, I would rank it to be a significant element of the Chandrayaan-1 mission.
M3 has found traces of water on the top few millimetres of the lunar soil. Is it true that Mini-SAR has located water in the permanently shadowed polar regions of the moon?
All I can say is that the data quality of Mini-SAR is excellent. Calibration studies suggest extremely good response of the detector elements and we are currently analysing the data.
Compared with the contemporary lunar missions from China and Japan, Chandrayaan-1s achievements seem to stand out. What are the reasons for this?
I feel a well-thought-out plan for addressing front-ranking scientific questions and excellent selection of both Indian and foreign instruments [are the reasons].
I do not have much details of the Chinese mission. However, the Japanese mission, Kaguya, has yielded extremely important lunar science results, which are published and have considerably improved our knowledge about the moon. It is just that the finding of the hydroxyl molecule is so exciting and novel that Chandrayaan-1 is having an edge.
Other than portraying the breathtaking views of the moons surface features, in what way are the pictures taken by the Terrain Mapping Camera (TMC) of India useful?
The three-dimensional images provided by the TMC are extremely important to advance our understanding of the lunar processes and the evolution of the different landforms on the moon. More importantly, the three-dimensional lunar surface topography needs to be considered in the analysis of data from most of the Chandrayaan-1 instruments.
The reflection of sunlight, received by the three detectors on board, from a nearly flat lunar surface will be very different from that coming from a close-by inclined surface, even if both have similar compositions. The TMC helps in removing such ambiguity.
What new features of the lunar far side have the high resolution 3-D camera of the TMC produced?
We have a lot of features. However, it is too early to identify any one as more interesting than the other. We shall be looking at the TMC images of both the front and far sides of the moon to identify a plausible site for the Chandrayaan-2 landing module.
Will you explain in laymans terms how the Indian Hyperspectral Imager (HySi) data will complement M3s data?
I do not think I have made this statement. So no specific answer.
Do you think the presence of water signifies the plausible presence of micro-organisms on the moon?No.
With what accuracy do we know the height of the mountains and hills on the moon or the depth of its craters and valleys with the help of the Lunar Laser Ranging Instrument (LLRI)? How will it be helpful in future missions?
The LLRI data can be accurate up to five metres. However, when we talk about the exact height we also need to know the orbit of the spacecraft accurately as a function of time. People are doing this synthesis now and a plan is on to bring out a topographic/height map of the lunar polar region from the LLRI data and complement the same with the TMC data for other regions.
How useful was the HEX instrument in this regard?
The HEX was included to check the basic hypothesis of poleward movement of volatiles on the lunar surface using a naturally occurring volatile (radon-222) from the decay of uranium present in the moon. It was not to search for water but to confirm that if there are water molecules on the moon they should drift poleward.
We could get data from about 200 passes over the polar region and the results are being studied. Unfortunately, the time of observation is much less than what is needed to give a firm idea of the nature of such a drift. However, we are hopeful that we can provide an upper limit on the magnitude of poleward movement of volatiles.
How useful is the experience of Chandrayaan-1 in designing Chandrayaan-2, which will have a lander and two rovers?
Obviously, it will be useful. A more detailed answer can only come from the team planning Chandrayaan-2.
How fruitful was Indias collaboration with the other space agencies that flew payloads on Chandrayaan-1?
ISRO has made a major impact with its openness for international collaboration in planetary exploration in its very first mission. I personally feel it was a very rewarding experience.
The interactions between the teams are excellent. Identified Indian co-investigators will have access to the data of all the foreign instruments and finally data from all the instruments will be archived in the Indian Space Science Data Centre in internationally accepted format for access to any interested scientist in India or abroad.
Chandrayaan-1 is now considered a classic example of international collaborations in planetary exploration with three space Agencies [ISRO, NASA and European Space Agency] and scientists from close to a dozen countries participating in the mission.