Universe extraterrestrial life

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. 

At the end of the day, the question of extraterrestrial life is based on two principles the Copernican principle and the mediocrity principle. The first states that the Earth is not in a central, specially favoured position. The mediocrity principle states that life on Earth is nothing special, so that life (in whatever form) could evolve in many places in the universe. 

Dick, Steven J. 1996. The Biological Universe The Twentieth-Century Extraterrestrial Life Debate and the Limits of Science. New York Cambridge University Press. 

Hydrogen, as an indicator of the presence of water, plays a role in the search for extraterrestrial life. In an October 1992 story about NASA s then newly computerized search for intelligent life in space, Newsweek noted that the ongoing search by the planetary researcher Paul Horowitz was focused on hydrogen s frequency of 1420 megahertz. This simplest and most abundant atom in the universe, Newsweek explained, vibrates at a frequency of 1,420,405,751 cycles a second, a frequency that Horowitz says would make sense as a meeting place in the vast radio spectrum. 8... 

Ghyba, Ghristopher. The New Search for Life in the Universe. Astronomy 38, no. 5 (May, 2010) 34-39. A well-illustrated article written for the nonscientist describing the fundamentals of the science of astrobiology and the search for extraterrestrial life. 

One of the biggest unanswered questions in science is whether we are alone in the universe. Most scientists are convinced that we are not alone, that extraterrestrial life does exist. One of the major reasons for conducting chemical analyses of other planets and moons is to find out if conditions on those bodies are conducive to life as we know it on Earth. 

Maser transitions have been observed in many important molecules and have been used to carry out surveys of the entire sky. The 22.235 GHz water maser transition is the strongest transition in the radio universe and represents an interesting candidate for an interstellar broadcast frequency. If extraterrestrial intelligence is trying to communicate with us, the choice of the broadcast frequency is an important one and would be known to all intelligent life. Of course it would have a different label, 22.235 GHz being a distinctly Earthly label, but it is a fundamental transition frequency and is observed everywhere. Other maser transitions include the 6.7 and 12.2 GHz methanol maser, the SiO maser v = 1, J = 7-6, 301.8 GHz, which occurs between levels in the first vibration state of the SiO molecule, and finally the OH maser first discovered in 1963 and buried deep in the 2n3/2 electronic state of the hydroxyl radical near 18 cm. This is actually four transitions at 1612, 1665, 1667 and 1720 MHz, all of which must be seen as a group but not necessarily of the same intensity. 

The extent to which biochemical systems are genuinely universal is, of course, an unresolved question. Many biologists, I suspect, would not be overly surprised to find close analogs to the citric acid cycle operating in extraterrestrial biospheres. On the other hand, most would be surprised, possibly astonished, if those similarities extended, for example, to signal transduction and respiratory proteins. So how do we proceed Even the resolution of life on Mars is probably many years in the future, and the likelihood of visiting exoplanetary biospheres is still centuries away. 

Furthermore, does an intrinsic reason exist in our world to exclusively use the L-amino acids instead of the D-series It is remarkable that the amino acids isolated from extraterrestrial organic matter from meteorites that are at least somewhat carbonaceous are slightly enriched in the enantiomers of the same L-series as those present in the amino acids of living organisms (Pizzarello, 2004). This would become a serious question only once we have discovered a few other life-forms in the universe and found them all to be based on L-amino acids. I know that others have a different point of view and consider the origin of chirality and of homochirality to be an important problem. I think it is not, in contrast with some related but simpler questions, such as that of the propagation of homochirality. 

Water is one of the basic elements for life. It is even assumed that the evolution of life is only possible if there is liquid water present. A water molecule has some remarkable properties that make it quite unique in the universe. In the first chapter of this book we will review these basic properties of water and the role of water on Earth. All ancient civilizations realized the importance of water and their cities were constructed near great reservoirs of water. But is water unique on Earth Do we find water elsewhere in the solar system, on extrasolar planetary systems or in distant galaxies We will start the search for the presence of extraterrestrial water in our solar system. Surprisingly enough it seems that water in some form and sometimes in only minute quantities is found on any object in the solar system. Even on the planet nearest to the Sun, Mercury, there may be some water in the form of ice near its poles where never the light of Sun heats the surface. And there are objects in the solar system that are made up of a large quantity of water in terms of their mass, like comets and several satellites of the giant planets. 

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