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Fruits of Exploration of Moon and Neighbouring Planets of the Solar System

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Fruits of Exploration of Moon and Neighbouring Planets of the Solar System FOURTH SILVER JUBILEE LECTURE 20 TH NOVEMBER 1974 FRUITS OF EXPLORATION OF MOON AND NEIGHBOURING PLANETS OF THE SOLAR SYSTEM BY D. LAL Physical Research Laboratory, Navrangpura, Ahmedabad-380009 Published by BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY LUCKNOW ISSUED 1976 FRUITS OF EXPLORATION OF MÖON ANÖ NEIGHBOURING PLANETS OF THE SOLAR SYSTEM BY D. LAL ; Physical Research Laboratory, Navrangpura, Ahmedabad-380009 Published by BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY LUCKNOW ISSUED 1976 FOURTH SILVER JUBILEE LECTURE FRUITS OF EXPLORATION OF MOON AND NEIGHBOURING PLANETS OF THE SOLAR SYSTEM by D. LAL IASED on results of recent explorations subsequently subjected to extremes of pres- of the Moon and other planets, it has sure or temperature. The inscription is now been demonstrated that one can made by particles which are omnipresent in derive a lot of quantitative information about space. We call these particles by different the palaeontology of the solar system. So names depending on where they originate; similar are some of the modern techniques e.g. solar wind, solar cosmic radiation or that have been used to those employed by galactic cosmic radiation. In each case we the great palaeobotanist, Professor Birbal are dealing with fast particles of atomic Sahni, that I would assert that, had nuclei; they are accelerated by stars like we been fortunate enough to have him our Sun. The interactions between the amongst us today, he would have been most particles and the rock are the basis for writ- delighted to learn of these new palaeonto- ing of the history of the conditions under logical methods used and of the advances which a rock evolved. made by space scientists. In the case of the earth, the fossil evidence The star of our show today is going to be is very rich indeed. But this is due to the a piece of rock; a mere rock. I would first fact that earth has an atmosphere and it has like to state, and subsequently qualify it, water. Further, since over long periods of that a rock contains usually, not only the time the earth has been the abode of a great geological records of the planet it derives variety of life, the record is very rich. We from, but also very valuable information now know that Moon has no atmosphere, it about the early birth and subsequent has no water and so far no evidence for life evolutionary history of the Sun and its has been found on the Moon. Considering planets. these facts, one may be tempted to say that Today my main attempt is to try to show the fossil record on the Mbon could hot be you that in the absence of an atmosphere on very interesting. However, this conclusion the planet, any rock which one derives from is erroneous. Recently, we have learnt that its surface contains not merely the fossil the information contained in lunar rocks, record of the time when the rock cooled ' provided one is ingenious enough to read it, down and about the average magnetic field is tremendous; what we have been able to which was present at thai, time but, in addi- leárn so far is probably only a small part of tion, it will also record a greater variety of the total information which is contained in physical processes which have occurred a rock. throughout the entire history of the existence As mentioned, in the case of the earth the of the rock itself. This record is, curiously fossil evidence owes its existence, largely to enough, written continuously in the rocies the fact that earth has an atmosphere, water and can be deciphered unless the rock was and other things (e.g. magnetic field) which FRUITS OF EXPLORATION OF MOON AND NEIGHBOURING PLANETS makes the terrestrial record very rich. In Let us begin with some discussions on the the case of the Moon however, we have a nature of lunar samples. The intellectual great variety of particles coming to it from man, even before acquisition of the lunar remote regions of the universe and these samples, has always been on the look out for particles alter the lunar rocks in many diffe- samples from extra-terrestrial environments. rent ways. These records are not found in This it, not just a curiosity. It is a very im- earth rocks and hence earth and moon rocks portant step in learning about the universe provide complementary information. The because we want to know about its composi- reason why the particle record is not seen in tion, we want to know about its evolutionary earth rocks is due to the fact that the earth history. How old is the Universe, has the has an atmosphere which acts as a shield; Universe existed for an infinity of time, are the large variety of particles which are inci- among an infinity of questions man has dent on the Moon are also incident on the asked of himself. What is the relevance earth but they can not reach the surface due of these questions to the study of lunar to energy dissipation or fragmentation in the rocks ? earth's atmosphere. Based on a superficial probing, one may Essentially, on the earth, we are leading not see how these cosmic questions could a very shielded life. We are not only shield- possibly be answered by examining a rock ed by the ceilings of our houses but we are from the solar system. But as we will soon also shielded by the atmosphere, which pro- see, a rock does contain plenty of useful in- tects us in many ways. We shall see how formation, and that is why scientists have important this shielding is, today. been trying to get " material" samples from Moon has no atmosphere. The total outside the earth. Whenever we see star- amount of lunar air, or whatever you call it, light, we see electromagnetic radiations is less than lö"la mm of mercury. Today which are indicative of the matter present it has essentially a zero dipolar magnetic in the Sun, stars and all other types of field. So even the lowest energy particles heavenly objects. When air from very high from Sun can directly reach the surface of altitudes is filtered, one finds dust in it. the Moon without any hinderance at all and Scientists have been trying to find out it is for this reason that the moon rocks whether some of this dast derived from cos- have been so important. For some reasons, mos. Meteorites constitute substantial sam- this is rather a technically involved issue. ples of matter which conies to the earth from These things are never brought to light in outside. Being th?. largest samples of cosmic general discussions which are published in matter easily available for scrutiny, they technical magazines or newspapers because have been studied extensively using a variety the news writers find these points too com- of techniques. But, not unexpectedly, only plicated and involved. ' a casual importance has been given to meteo- With all this realization, considering on rites in the pre-Apollo epoch, since whenever the one hand the Leveral recent advances in a thing becomes available in plenty, one loses space physics and the realization that rocks sight of its importance. The field of meteo- are good record keepers of the geological ritics is more than a century old and there history of a planet and considering on the are more than 1500 different known meteo- other hand that palaeobotany is indeed and rites in museums. The lunar samples, on has been the main research area óf this insti- the other hand are clearly recognized to be tute, I embarked on the difficult task of pre- very valuable because of the costs involved senting this talk as one of the annual Silver in reaching the Moon and bringing them back Jubilee Lectures of the Institute, to the earth. In our laboratory, we were FRUITS OF EXPLORATION OF MOON AND NEIGHBOURING PLANETS prepared to undertake an extensive detailed by a hypervelocity impact of a fast particle and painstaking study of lunar samples even from that due to the emission of hot volcanic if *ve had been given only a few milligrams. material. Next time you see photographs Everywhere, prior to the happening of the of the surface of the Moon, mercury or mars, successful Apollo 11 mission which brought examine them carefully and contrast them back tens of kilograms of lunar rocks/soil with the volcanic craters we see on the earth. samples, scientists were attempting to deve- Also, a keen observer will immediately ask lop completely new technologies so that some- the question why one sees so many craters thing very exciting could be learned even if on the Moon or Mars, but so few on the only very small amounts of lunar samples earth. were returned in the manned lunar missions. In a distant picture of the Moon, as in And this had very interesting consequences. PI. 1, one can clearly see something like 15 Because, ignoring for the time being, what one large craters. Such photographs of the Moon has learned from studies of moon samples, were taken long before the Apollo landings. the technologies that have been developed But, in fact, the entire face of the Moon is have opened up new scientific frontiers. pocked with craters. This becomes clear For example, from an analysis of about 1 when one takes a look at photographs of the mg of rock sample one can. determine the surface of the Moon taken at shorter and chemical composition of something like ten shorter distances.
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