Solar System Life

Interestingly, many hyperthermophiles also are highly salt tolerant. This is an adaptation to life involving aqueous systems that evolve with high-pressure liquid/vapor and supercritical fluid-phase separation of hydrother-mally heated seawater. Both psychrophiles and hyperthermophiles have large numbers of species that also require heavy-metal tolerance, due to the concentration of heavy metals by the thermodynamic phase-separation processes operative in both very cold and very hot aqueous systems (Breezee et al. 2004 Kaye and Baross 2002 Summit and Baross 1998). 

The situation in Europa s and Enceladus ice-covered oceans or aquifers is very different from those on Earth and Mars. Energy availability to drive aqueous conditions seems not to be a problem, as tidal dissipative heating of both satellites appears to have maintained liquid layers for perhaps billions of years. The likelihood is that hydrothermal vent activity on the sea floors of both satellites is prodigious. However, we know very little about the chemistry 

Curiously, Enceladus, seemingly the least likely of the Solar System s water worlds, may be the very last refuge of life in this Solar System. This is because its energy is independent of the Sun just pure tidal energy ulti- 

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Resource pessimists counter that this process cannot proceed forever because the eternal persistence of demand for any given commodity that is destroyed by use must inevitably lead to its depletion. I lowever, the eternal persistence assumption is not necessarily correct. The life of a solar system apparently is long but finite. Energy sources such as nuclear fusion and solar energy in time could replace more limited resources such as oil and natural gas. Already, oil, gas, nuclear power, and coal from better sources have displaced traditional sources of coal in, for example, Britain, Germany, Japan, and France. 

These isotopes are sometimes used as tracers of natural terrestrial processes and cycles. Long-lived isotopes, such as Rb and Sm are used for precise dating of geological samples. When the solar system formed it also contained several short-lived isotopes that have since decayed and are now extinct in natural systems. These include Al, Fe, Pu, Pd, and Al with a half-life of less than a million years is particularly important because it is a potentially powerful heat source for planetary bodies and because its existence in the early solar system places tight constraints on the early solar system chronology. 

Speculation about life on other planets probably began when humans discovered that the Earth Is not unique. We know that several other planets of the solar system bear at least some resemblance to our own. Why, then, should there not be life on Mars, or Venus, or perhaps on undiscovered Earthlike planets orbiting some other star ... 

How can scientists collect experimental evidence about possible life on another planet Sending astronauts to see for themselves is impractical at our current level of technology. Nevertheless, it is possible to search for life on other worlds without sending humans into space. In the late 1970s, NASA s Viking spacecraft lander collected a sample of dirt from Mars, the planet in our solar system most like Earth. The sample showed no signs of life. Nevertheless, speculation continues about Martian life. 

Outside our own solar system, might there be planetary environments where life flourishes hi recent years, astronomers have discovered planets orbiting stars other than our own. Whether or not these planets support life is still impossible to say. Nevertheless, the more we discover about the variety of the universe, the more likely it becomes that we are not alone. 

The Zag meteorite fell in the western Sahara of Morocco in August 1998. This meteorite was unusual in that it contained small crystals of halite (table salt), which experts believe formed by the evaporation of brine (salt water). It is one of the few indications that liquid water, which is essential for the development of life, may have existed in the early solar system. The halite crystals in the meteorite had a remarkably high abundance of 128Xe, a decay product of a short-lived iodine isotope that has long been absent from the solar system. Scientists believe that the iodine existed when the halite crystals formed. The xenon formed when this iodine decayed. For this reason, the Zag meteorite is believed to be one of the oldest artifacts in the solar system. In this lab, you will use potassium-argon radiochemical dating to estimate the age of the Zag meteorite and the solar system. 

The presence of water as solid, liquid, and gas is a feature that makes Earth unique in the solar system and that makes life possible as we know it. The transport of water and the energy exchanged as it is converted from one state to another are important drivers in our weather and climate. One of the key missions is to develop a better understanding of the global water cycle at a variety of scales so that we can improve model forecasts of climate trends,... 

The question of the origin of life on Earth leads directly to the question of the formation of our planet, of the solar system and of the universe. The ancient philosophers, as we have seen, attempted to answer such questions, but the models which we discuss and argue about today were proposed by scientists only in the last century. 

Cronin J (1998) Clues from the origin of the Solar System meteorites. In Brack A (Ed.) The Molecular Origins of Life. Cambridge University Press, p 119-146 Cronin J, Pizzarello S (2000) Orig Life Evol Biosphere 30 209 Dalgamo A (1991) Nature 353 502 Delsemme (1984) Orig Life Evol Biosphere 14 51... 

Although the terms exobiology and astrobiology really mean the same thing, astro-biology , introduced by NASA in 1995, has become the one of choice. This branch of science reaches from cosmochemistry via biogenesis to all the other themes involving research on traces of life (of whatever sort) on planets and on moons, both within and outside our solar system. 

Life which exists, or could exist, outside our Earth is generally known as extraterrestrial life. A distinction is also made between life (or possible life) within or outside the solar system. In spite of what is claimed in many science fiction books and films, there is no single piece of evidence for a living system outside Earth. The coming years and decades will hopefully provide clarity on the question as to whether we are really alone in the universe or not. 

There are three objects within the solar system which are the subject of research on possible extraterrestrial life, traces of life, biomolecules or their precursors ... 

Of the three extraterrestrial targets in our solar system, the Saturnian moon Titan is the least likely to provide signs of life. To quote Christopher McKay from the NASA Ames Research Center, Titan is an interesting world. For example, its organic haze layer could be an example of the prebiotic chemistry which led to life on Earth . Direct links to extraterrestrial life have not, however, yet been found, as water (one of the main preconditions for life) has not been detected on Titan, apart from traces of water vapour in the higher layers of the Titanian atmosphere (Brack, 2002). 

The search for extrasolar life requires us to find planets outside the solar system. But since stars are only visible as small dots of light, it will be very difficult to find planets in outer space, since these do not emit light. This is true even for the nearest star, Alpha Centauri, which is about 4.3 light years away (roughly 7,000 times the distance from the sun to Pluto). 

It is assumed that the greatest part of our solar system, and indeed of the Milky Way, is hostile to life. The term habitable zone (Franck et al., 2002) takes into account... 

Interplanetary panspermia the transport of life forms within the solar system Interstellar panspermia the transport from one star to another... 

The Sun formed some 4.5 Gyr ago (Gyr is a Gigayear or 109 years) from its own gas cloud called the solar nebula, which consisted of mainly hydrogen but also all of the heavier elements that are observed in the spectrum of the Sun. Similarly, the elemental abundance on the Earth and all of the planets was defined by the composition of the solar nebula and so was ultimately responsible for the molecular inventory necessary for life. The solar system formed from a slowly rotating nebula that contracted around the proto-sun, forming the system of planets called the solar system. Astronomers have recently discovered solar systems around... 

There is no one correct theory for the origin of life on Earth or any habitable planet, although many have been presented. The current set of ideas is summarised in Figure 1.5. Aside from the theory of creation, which seems particularly hard to test, the testable theories of the origins of life divide into two extraterrestrial or panspermia, the theory that life was seeded everywhere somewhat randomly and terrestrial, that life originated de novo on Earth or other habitable planets around other stars. The theories of terrestrial origin are more favoured but the recent discovery of habitable planets and life within any solar system suddenly makes panspermia more likely. 

The interstellar medium is thus a chemically diverse medium fed nearly all of the chemical elements by supernova explosions. Conditions in the interstellar medium produce a cocktail of molecules that ultimately find themselves back on the surface of planets during the formation of the new star and solar system. Does the interstellar medium seed life with molecules from space The nature of interstellar medium chemistry might then add credibility to the formation of life in many places within the Universe and act as a panspermia model for the origins of life. 

The half-life is independent of the initial number of nuclei. For 14C decay the half-life is 5717 years, whereas the 238U decay half-life is 4.5 billion years. Carbon dating works well for timescales in the recent past and is used for dating objects such as the Turin shroud, but 238U is better for timescales of the age of the solar system. 

The analysis of the laboratory ice experiments reveals a diverse array of bio-logical-looking molecules with the potential to seed life. Cometary collisions with planets could deliver these molecules to a primitive Earth or indeed to all planets within the solar system. The frequency of the collisions depends somewhat on the local star and the structure of the solar system forming around it. 

It is tempting to take a tour of the solar system, stopping off at each planet to look at the chemistry from the origin of the red colour in Jupiter s great red spot to the volcanic activity of Io, but this would be another book for each planet. Instead, we will generalise the study to the formation of Earth-like planets in order to focus on the possibilities for life. 

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