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The Forefront of Space Science

Search for Life in Space, See Space in Life -Theme of Biological Sciences in Space- Masamichi Yamashita, ISAS
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I am concerned that the trend of establishing quantitative targets or assessments for academic research results, such as "Japan should win a certain number of Nobel Prizes in the following XX years," is increasing too much in our society today. Therefore, I hesitate to start with numbers, but I have counted and classified the scientific fields on the pictures of front covers of sixty copies, published in about one year, of "Science" and "Nature", magazines that cover a wide range of scientific fields. Weighing the value by the number of front cover pictures is not consistent with my daily approach where I loudly scold my own child for being carried away with comic books, and encourage my child to read real books. Nevertheless, my results are 60% for biology; 23% for space/planets/earth; 9% for material science/chemistry/material; and 4% for fundamental physics. Biological sciences in space are related to two fields, biology and space/planet/earth, and I would insist on its importance by citing the front covers. But, rethinking that biological sciences in space can be the product set of these two fields, I would like to explain what its central themes are. The title above is a catchphrase using simple words that modify the main theme, "Exploring Extraterrestrial Life and Understanding Life with Different Principles", of the opening lecture of the Japanese Society for Biological Sciences in Space (JSBSS) held in November 2003.

Search for life in space

All living things have parents, and their parents have parents. In this way, there is no spontaneous generation. If this is true, we must draw a picture of how life first originated on earth or other celestial bodies as a process following chemical evolution in space history and interstellar space. The artificial synthesis of parasitic viruses has already been reported, but the perfect synthesis of cellular life forms, which can maintain their own autonomous lives, has not yet been achieved. The more the life mechanism of cells is elucidated, the more a major missing link between pre-biotic precursors and primitive cells is recognized. As for the origin of life, there is a hypothesis that meteorites, which were generated in interstellar space and contained many precursors, landed on earth and, then, reacted with water, creating all the components of life forms at once in a high density. Also, research is now being carried out seeking a model of life in the highly specific physical and chemical environment around the deep-sea hydrothermal vents. Earth¬s very active crustal movements have erased information about the primitive life forms and the environment that generated primitive life. The reason why we search for life in space is to answer the question whether or not life forms exist, or existed, on celestial bodies other than Earth, and to respond to expectation of discovering life¬s origin and its environmental conditions.

Living things on Earth, which have evolved into many kinds of life in a variety of forms, can be traced back to common ancestor. Living things on Earth have conservatively inherited mechanisms and biochemical materials that were once obtained. There are cases as if living things arbitrarily select, for example, which optical isomer should be selected to form their bodies and what combination of amino acids should be used. Concerning the elements composing living things, we can find the composition corresponding to the solar system and its planet, Earth. The COSPAR life science section called the study to explore if the principle of life on Earth is limited to Earth with focusing on defining factors which Earth as a planet has given for the origin and evolution of living things as Planetary Biology. Even if the combination of elements composing living things varies, species and evolution, which are the fundamental concepts of biology, may be the universal principles for life from the viewpoint of space. It is effective to search for life on other celestial bodies and compare it with life on earth in order to scientifically verify this hypothesis. For this purpose, it may be a faster way to discover living species, of which ancestors are different from other living things, in the isolated environment on earth.

Sensation of Mars meteorites

The report on meteorites estimated to have originated on Mars, which were collected in Antarctica, has provided a major impact on research and caused us to think this over. Some new findings indicating the possibility of life on Mars were found in the meteorites. One finding is the structure, which looks like a trace fossil of microorganism, shown in the cleaved surface of the meteorites. Many scientists pointed out that the physical size of the structure is far smaller than that of bacteria on earth. The biggest focus of our research is to explore living things that stand on different principles from living things on earth. So, it is ironic that scientists criticize that living things on Mars are different from those commonly seen on earth.

With this argument continuing, a workshop was held in the U.S.A. to conjecture the size of the smallest living things. The information amount required for autonomous, not parasitic, living things to maintain their life and make autoreproduction was estimated, and then translated to the amount of molecular coding such information. Further, mechanisms to develop information and cell membranes, boundaries for dividing oneself from others, were added, and the limits on the sizes of living things were examined. The work was to inversely assemble life, to build living things from information already known. The estimated size was not largely different from that of mycoplasma, which is the smallest autonomous living thing known. Cellular organs constructing cells were once independent living things respectively. Some time in the past they were taken in and began to live symbiotically. The workshop concluded that, if we seek small living things, we should envision a world where cellular organs were independent living things and some living things symbiotically maintained life. In order to discover and understand living things standing on entirely different principles, needless to say that we should base our work on an in-depth understanding of life, we should maintain free thinking that is not constrained by established knowledge.

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