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Xenobiology (also known as exobiology or astrobiology) is the term for a speculative field within biology which considers the possible variety of extraterrestrial life. It also includes the concept of artificial life, since any life form that might naturally evolve elsewhere could conceivably be created in a laboratory using a future technology. It might be difficult to tell whether a truly strange 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 rest of 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 it possible to do exploratory engineering of alternate life 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 number of 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 of the 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 the universe then there should be obvious signs of it.

Xenobiology also figures in much science fiction as the fictional science of the biology of alien organisms. This use of the term demonstrates the speculative generation of possible models of such life, e.g. silicon-based.

Search for evidence of extraterrestrial life

There is no current tangible evidence for intelligent extraterrestrial life (as of 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 that interpretation 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 well as by the Mars Express probe. Methane has a relatively short half-life in the Martian atmosphere, so there must be a recent source of it. Since one possible source, active volcanism, has thus far not been 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 on other planets in our solar system.

NASA Astrobiology Institute

The NASA Astrobiology Institute (NAI) engages in government-funded xenobiologic study of the living universe. Advances in science and technology are yielding dramatic new knowledge about the origin, distribution, and destiny of life. 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 at environmental extremes such as in Antarctic rocks, boiling hot springs, and aquifers buried kilometers below the land surface. We have found that liquid water, the one essential ingredient for life as we know it, once flowed on the surface of the planet Mars and exists today below the icy crust of Jupiter's moon, Europa. Life on Earth has been traced back 3.8 billion years to the period of heavy cometary bombardment, an era that simultaneously brought life-giving water and organic compounds to the terrestrial planets while battering them with lethal quantities of impact energy. We are discovering both the fragility and robustness of life as we investigate the history of mass extinctions on our planet (including extinctions taking place today), the subtle alterations in climate triggered by volcanic eruptions and human industry, and the destruction 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 can influence or even create life. The ramifications of the recent discovery that Mars was once quite wet has caused quite a stir in the astrobiological community. More than this, an astrobiologist wants an answer to the question "How does life arise?" He may model a galaxy's lifetime, or part of it, to see which stars are formed where, how they orbit, 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 in with the age of stars - An old star was formed before supernovae had enriched the locale with metals. Astrobiology is truly a diverse discipline (being young), yet intensely relevant.

The Astrobiology Institute's focus is multidisciplinary in its content and interdisciplinary in its execution. Its success depends critically upon the close coordination of diverse scientific disciplines and programs, including space missions. The fundamental questions that astrobiology attempts to answer are these:

  • How do habitable worlds form and how do they evolve?
  • How did living systems emerge? How can we recognize other biospheres?
  • How have the Earth and its biosphere influenced each other over time?
  • How do rapid changes in the environment affect emergent ecosystem properties and their evolution?
  • What is the potential for biological evolution beyond the planet of origin?

NAI claims to encourage planetary stewardship through an emphasis on protection against forward and back biological contamination 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 deeper understanding of life, searching for extraterrestrial biospheres, assessing the societal implications of discovering other examples of life, and envisioning the future of life on Earth and in space.

See also

External links

General subfields within biology

Anatomy | Bioinformatics | Botany | Ecology | Evolutionary biology | Genetics | Marine biology | Human biology | Cell biology | Microbiology | Molecular biology | Biochemistry | Origin of life | Paleontology | Physiology | Taxonomy | Xenobiology | Zoology

Last updated: 10-24-2004 05:10:45