Xenobiology (also known as exobiology or astrobiology) is the term for aspeculative field within biology which considers the possible variety of extraterrestrial life . It also necessarily includes the conceptof artificial life , since any life form that might naturally evolveelsewhere could conceivably be created in a laboratory using a future technology. It might be difficult to tell whether a trulystrange life form had in fact arisen in space, or was designed much nearer to home.
Although this is currently a speculative field, the absence of life in the restof the Universe is a falsifiable hypothesis (though it is yet to be proven false), making xenobiology a valid field for scientific enquiry. Likewise, computer simulations of basic life processes have made itpossible to do exploratory engineering of alternatelife forms (like left-handed DNA) to determine their characteristics.
For these reasons the search for extraterrestrial life is of great relevance to xenobiologists. Some contend that the numberof planets with intelligent extraterrestrial life can be estimated from the Drake equation if and when we ascertain the values of its variables. However uncertainties in the term ofthe equation make it impossible to predict whether life is rare or common. Another associated topic in xenobiology is the Fermi paradox , which suggests that if intelligent life is common in theuniverse then there should be obvious signs of it.
There is no current tangible evidence for intelligent extraterrestrial life ( asof 2004 ). However examination of meteors from Antarctica which are presumed to have originated from the planet Mars have provided what some scientists believe to be microfossils of extraterrestrial life, although thatinterpretation of the evidence is still controversial. In 2004 , the spectral signature of methane was detected in the Martian atmosphere by both Earth-based telescopes as wellas by the Mars Express probe. Methane has a relatively short half-life inthe Martian atmosphere, so there must be a recent source of it. Since one possible source, active volcanism, has thus far notbeen detected on Mars, this has led scientists to speculate that the source could be (microbial) life.
Missions to other planets (such as Spirit and Opportunity to Mars, Cassini to Saturn's moon Titan , and a future mission to Jupiter's moon Europa ) hope to further explore the possibilities of life onother planets in our solarsystem .
NASA Astrobiology Institute
The NASA Astrobiology Institute (NAI) engages in government-funded xenobiologic study of the livinguniverse. Advances in science and technology are yielding dramatic new knowledge about the origin, distribution, and destiny oflife. Scientists have analyzed complex organic chemistry in interstellar clouds of gas and dust and have discovered more than 200 planets outside of our solar system. Life on Earth has been found thriving atenvironmental extremes such as in Antarctic rocks, boiling hot springs, andaquifers buried kilometers below the land surface. We have found that liquid water, the one essential ingredient for life as weknow it, once flowed on the surface of the planet Mars and existstoday below the icy crust of Jupiter 's moon, Europa . Life on Earth has been traced back 3.8 billion years to the period ofheavy cometary bombardment, an era that simultaneously brought life-giving water and organic compounds to the terrestrial planetswhile battering them with lethal quantities of impact energy. We are discovering both the fragility and robustness of life as weinvestigate the history of mass extinctions on our planet (includingextinctions taking place today), the subtle alterations in climate triggered by volcanic eruptions and human industry, and thedestruction of our planet's protective shield of ozone.
NAI astrobiology is, then, a macro-system focused discipline. It seeks to understand the very large scale processes which caninfluence or even create life. The ramifications of the recent discovery that Mars was once quite wet has caused quite a stir inthe astrobiological community. More than this, an astrobiologist wants an answer to the question "How does life arise?" He maymodel a galaxy 's lifetime, or part of it, to see which stars are formed where, how theyorbit, and whether they avoid the energetic (and quite deadly) galactic center. Astrobiologists are interested in metallicity of stars since a star with a high metallicity is very likely to have planets. This ties inwith the age of stars - An old star was formed before supernovae had enriched thelocale with metals. Astrobiology is truly a diverse discipline (being young), yet intensely relevant.
Astrobiology Insitute's focus is multidisciplinary in its content and interdisciplinary in its execution. Its success dependscritically upon the close coordination of diverse scientific disciplines and programs, including space missions. The fundamentalquestions that astrobiology attempts to answer are these:
MAI claims to encourage planetary stewardship through an emphasis on protection against forward and back biologicalcontamination and recognition of ethical issues associated with exploration.
NAI literature says it recognizes a broad societal interest in its endeavors, especially in areas such as achieving a deeperunderstanding of life, searching for extraterrestrial biospheres, assessing the societal implications of discovering otherexamples of life, and envisioning the future of life on Earth and in space.
Xenobiology also figures in much science fiction as the fictional science of the biology of alien organisms. This use of the termdemonstrates the speculative generation of possible models of such life, e.g. silicon -based.
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