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Space Weather: a new frontier in bioastronomy

J. Chela-Flores 1 and M. Messerotti 2
1. The Abdus Salam International Centre for Theoretical Physics,
Trieste, Italy and
Instituto de Estudios Avanzados, Caracas 1015A, Venezuela
2. INAF-Trieste Astronomical Observatory,
Trieste, Italy

A step forward in origin of life studies consists of taking the subject from organic chemistry into the domain of the life, Earth and space sciences. The subject of bioastronomy (astrobiology) has come of age due to the space missions of the last four decades: Mariner (in 1964 Mariner 4 was the first spacecraft to obtain and transmit close range images of Mars), Apollo, Vikings, Voyagers, and particularly the most recent ones, Galileo (focused on the Jovian system from 1995 till 2003) and Cassini-Huygens, which is currently sending valuable information from the Saturn system. New areas of research have come into existence as a consequence of this change of emphasis, such as planetary protection, whose aim is to prepare ourselves in advance for the sample-return missions from Mars and Europa. In the present work we would like to discuss a second novel area of research. The study of the origin of life is an interdisciplinary activity that requires a discussion of the conditions determined by the lithosphere, the hydrosphere, the atmosphere and, in the case of the Earth, the magnetosphere. These conditions depend on the conditions that are encountered in interplanetary space. These interplanetary environmental conditions have been called "Space Weather". In this Newsletter we would like to review briefly this additional factor that opens what may be called a new frontier in the sciences of life in the universe. Since aspects of observational astronomy are of paramount importance in the context of this brief review, we emphasize the work as bioastronomy rather than using the more comprehensive synonym that the present Newsletter and a large cross section of the researchers in this area have adopted.

HOW OLD IS LIFE ON EARTH?

In the photosynthesis of prokaryotes, including the stromatolitic-forming cyanobacteria, carbon dioxide is captured by a specific enzyme that leads in several steps to the synthesis of glucose. But the carbon dioxide in the environment and nutrients contain the two stable isotopes of carbon 12C and 13C. The process of photosynthesis favors 12C over 13C. Geologic process partitions the stable isotopes in opposite ways. For instance, limestone is depleted in 12C and enriched in 13C. The fossil records of organic matter that have been enriched in 12C can be traced back in sedimentary rocks to some of the earliest samples, such as the 3,800 Myr-old metamorphosed sedimentary rocks from Isua, West Greenland. These geochemical analyses of the ancient rocks argue for the presence of bacterial ecosystems in the period 3.8-3.9 Gyr BP.

WAS THERE CONTINUOUS LIFE ON EARTH SINCE THE HADEAN?

There are many reasons why we cannot be certain of the exact conditions in which life evolved on Earth. One important factor is what has been called 'the heavy bombardment period' in the early Solar System. Wherever conditions may have prevailed in the atmosphere, biosphere and lithosphere, they must have been altered significantly when a large number of large bodies collided with the early Earth. So much so that the Moon itself is believed to have been the product of a massive collision of the Earth and a Mars-like object. Entire oceans may have boiled off down to a depth of several kilometers. Large collisions persevered even after the heavy bombardment period. In fact, half a billion years after the Moon itself had been formed through a collision process, its Imbrium basin was formed by a large impact, as late as 3.8 Gyr BP. On the other hand, the Search of Extra Terrestrial Intelligence (SETI) opens the possibility for a first contact with new manifestations of life given the remarkable progress in signal detection. Besides, our understanding of our own Solar System has deepened significantly, following the discovery of a large number of extra solar planets. These aspects of observational astronomy underline the relevance of refining our insights into life origins, one of the main objectives of bioastronomy, by careful consideration of space weather.

QUESTIONS WHERE SPACE WEATHER IS RELEVANT

1. Most meteorites are of the stony kind, the so-called chondrites, as they contain chondrules (mineral-rich blobs). Amongst the chondrites the most ancient ones, contemporary with the formation of the Solar System, are rich in carbon and are, therefore, called carbonaceous chondrites, which include the all-important Murchison meteorite. There is a very important fraction of all the meteorites that have been collected on the surface of the Earth, whose origin has been estimated to be from the early Solar System. Meteorites are a possible source of delivery of amino acids and nucleotides. This possibility has been amply demonstrated by the organic chemistry analysis of the Murchison meteorite, as well as in other meteorites. There is a reasonable explanation for the source of the biomolecular precursors that were found in Murchison. Models of interstellar grain mantles support the view that organic compounds were synthesized in interstellar space, which in turn were to be delivered on planetary surfaces during the late accretion period. Experiments have shown that Space Weather has a significant role to play in this process, since UV radiation will drive the synthesis of photochemical processes. The oxygenation of the Earth atmosphere as well as the chemical and biological evolution of life was due to a large extent to solar UV radiation. Several processes were relevant with intensities proportional to the flux emitted by the Sun. The Standard Solar Model predicts that the solar flux of the early Sun was lower than the present one, whereas high-precision solar evolutionary models provide a value significantly higher than the present one. This 'dim-Sun' hypothesis should be ascertained by observation and experiment. This hypothesis is crucial since it may play a significant part in the evolution of atmosphere, biosphere and hydrosphere. Factors to keep in mind are, (a) those that may have catalyzed chemical evolution of life, and (b) factors that may have biased biological evolution. Furthermore, observational evidence on solar-like stars at different evolutionary stages indicate that during the time span, which is relevant to the appearance of life on Earth, namely the Hadean and early Achaean (4.5 to 3.5 Gyr BP), the early Sun might have experienced a highly active phase in its particle and radiation output. In any case the focus of experimental work has been on the synthesis of the main three organic compounds either by incorporation at the end of accretion, or by delivery of the precursors of the biomolecules that may have evolved on early planets that support life.

2. Stanley Miller, after some significant previous experiments by Melvin Calvin, attempted to create a model for the early Earth, in which it was postulated that the main components of the atmosphere were methane (as in the case of Titan, the Saturn giant satellite), ammonia, hydrogen and water. His experimental set up included a flask of water. The recipient was boiled to induce circulation of the gases. At the same time the experimental set-up was capable of trapping any volatile water-soluble products that were formed. An electric spark acted on the gases for a period of time. After suspending the electric discharge the water was found to contain several small organic compounds, two of which are found in all proteins: the amino acids glycine and alanine. Since the Miller experiment was concluded half way through last century, the debate has continued regarding the nature of the primitive atmosphere. Today, some arguments lead us to think that the original gases may not have coincided with those of the Miller experiment. What is more significant is that oxygen was missing. Had Harold Urey advised Miller to add oxygen to his gas mixture, no amino acids would have formed. Stanley Miller published his remarkable paper in 1953. Urey was responsible for the discovery of an isotope of hydrogen: deuterium. Urey had subsequently suggested that the early Earth had conditions favorable for the formation of organic compounds. Miller's experiment assumed that the prebiotic synthesis of biochemical was due to a process of chemical synthesis that took place in conditions that resembled the early Earth. Solar energy was imitated by an electric discharge. Subsequent work along these lines led to the synthesis of nucleic acid polymers. In a weakly reducing atmosphere, where little free hydrogen was present UV photons may interact with carbon dioxide, carbon monoxide and nitrogen with only a small amount of hydrogen. Thus the conditions of Space Weather have to be carefully orchestrated with the theoretical and experimental work in chemical evolution to gradually deepen our insights into life's origin. Indeed, in this case, as in the following one, Space Weather is likely to play an increasingly more relevant role in understanding the preservation and eventual inhibition of life on Earth.

3. RNA synthesis in a Miller type of experiment remains as a challenge. In spite of the underlying difficulties, the first living system of the early Earth has been conjectured to be RNA, a possibility that has been referred as an RNA world. The main motivation for supporting the RNA world is that not only RNA along with DNA have the possibility of codifying genetic information, but some RNAs have catalytic properties. This property has been confirmed even in modern organisms by the fact that in ribosomes RNA catalyzes protein synthesis. It still remains as a challenge to get deeper insights into the transition from chemical to biological evolution. The role of Space Weather remains critical for the preservation of life from its earliest microbial stages. Two factors are of paramount importance, the stability of both Sun and the Earth magnetic field. (Similar conditions will occur in other solar systems between the star and its terrestrial-like planets.) By the analysis of the late stages of the evolution of the Sun, we conclude, as we did in the previous point that Space Weather is likely to play an increasingly more relevant role in understanding the preservation and eventual inhibition of life on Earth.

4. The main sources of energy available for the processes that led to the first living cell are not only solar radiation, but also some alternatives to the Miller scenario were possible such as hydrothermal vents and volcanic lightning. After the appearance of the first cells, filamentous cyanobacteria living in the Achaean in colonial mats (stromatolites) began to oxygenate the atmosphere. Once again Space Weather considerations become of extreme importance, since solar UV radiation can break water molecules leading to oxygen and ozone, which will eventually protect the early stages of evolution from the highly energetic UV radiation. It all depends on our knowledge of the early Sun, so that we could have an accurate insight into the UV radiation that was being delivered.

References

Chela-Flores, J. (2004) The New Science of Astrobiology From Genesis of the Living Cell to Evolution of Intelligent Behavior in the Universe. Series: Cellular Origin, Life in Extreme Habitats and Astrobiology, 3, Kluwer Academic Publishers: Dordrecht, The Netherlands, 251 p., Soft cover edition of the 2001 book, ISBN: 1-4020-2229-8

Messerotti, M. (2004) Space Weather and Space Climate: Life Inhibitors or Catalysts? in "Life in the Universe", Seckbach, J., Chela-Flores, J., Owen, T. and Raulin, F. (eds.), Cellular Origin and Life in Extreme Habitats and Astrobiology, 7, Springer, Dordrecht, The Netherlands, pp. 177-180, 2004.

Messerotti, M. and Chela-Flores, J. (2004) Preliminary Identification of Space Weather Key Agents for the Emergence of Life in Exoplanetary Environments, First European Space Weather Week Conference, ESTEC, Noordwijk, The Netherlands, November 29-December 3, 2004.

Messerotti, M. and Chela-Flores, J. (2005) Solar Space Weather as a Factor in the Origin of the Biosphere, Abstract CD-ROM 'Geophysical Research Abstracts, Volume 7, 2005'.

References (supplement added in September 2006)

Chela-Flores, J. (2006). The sulphur dilemma: Are there biosignatures on Europa's icy and
patchy surface? ? International Journal of Astrobiology, 5, pp. 17-22.

Chela-Flores, J. (2007). Fitness of the cosmos for the origin and evolution of life: from biochemical fine-tuning to the Anthropic Principle, in "Fitness of the cosmos for life: Biochemistry and fine-tuning", John D. Barrow, Simon Conway Morris, Stephen J. Freeland and Charles L. Harper, eds., Cambridge University Press, in press.

Messerotti, M. and Chela-Flores, J. (2006a). Solar activity and solar weather in the framework of life origin and evolution on Earth To be published by ESA's Publication Division, Special Publication, in press.

Messerotti, M. and Chela-Flores, J. (2006b). Signatures of the ancient Sun constraining the early emergence of life on Earth. To be published by Springer, Astrophysics and Space Science Library (ASSL) Series.