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Astronomy

Main article: Astronomy

Artist's impression of the extrasolar planet OGLE-2005-BLG-390Lb (with surface temperature of −220°C) orbiting its star 20,000 light-years (117.5 quadrillion miles) from Earth; this planet was discovered with gravitational microlensing.

The planned NASA Kepler mission for the search of extrasolar planets

Most astronomy-related astrobiological research falls into the category of extrasolar planet (exoplanet) detection, the hypothesis being that if life arose on Earth then it could also arise on other planets with similar characteristics. To that end, a number of instruments designed to detect Earth-like exoplanets are under development, most notably NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin programs.^[27] Additionally, NASA plans to launch the Kepler mission in 2008, and the French Space Agency has already launched the COROT space mission.^[28][29] There are also several less ambitious ground-based efforts underway (see exoplanet).

The goal of these missions is not only to detect Earth-sized planets, but also to directly detect light from the planet so that it may be studied spectroscopically. By examining planetary spectra, it would be possible to determine the basic composition of an extrasolar planet's atmosphere and/or surface; given this knowledge, it may be possible to assess the likelihood of life being found on that planet. A NASA research group, the Virtual Planet Laboratory[1] (VPL), is using computer modelling to generate a wide variety of virtual planets to see what they would look like if viewed by TPF or Darwin. It is hoped that once these missions come online, their spectra can be cross-checked with these virtual planetary spectra for features that might indicate the presence of life. The photometry temporal variability of extrasolar planets may also provide clues to their surface and atmospheric properties. One mission was planned to Jupiter's moon Europa before recent cuts by NASA. This mission would have searched for life in the ocean of this moon.

An estimate for the number of planets with (intelligent) extraterrestrial life can be gleaned from the Drake equation, essentially an equation expressing the probability of intelligent life as the product of factors such as the fraction of planets that might be habitable and the fraction of planets on which life might arise:^[30]

However, whilst the rationale behind the equation is sound, it is unlikely that the equation will be constrained to reasonable error limits any time soon. The first term, Number of Stars, is generally constrained within a few orders of magnitude. The second and third terms, Stars with Planets and Planets with Habitable Conditions, are being evaluated for the sun's neighbourhood. Another associated topic is the Fermi paradox, which suggests that if intelligent life is common in the universe, then there should be obvious signs of it. This is the purpose of projects like SETI, which tries to detect signs of radio transmissions from intelligent extraterrestrial civilizations.

Another active research area in astrobiology is solar system formation. It has been suggested that the peculiarities of our solar system (for example, the presence of Jupiter as a protective shield or the planetary collision which created the moon) may have greatly increased the probability of intelligent life arising on our planet.^[31][32] No firm conclusions have been reached so far. The role of Jupiter may be controversial. [2]

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Biology

Main article: Biology

Hydrothermal vents are able to support extremophilic bacteria on Earth and may also support life in other parts of the universe.

Extremophiles (organisms able to survive in extreme environments) are a core research element for astrobiologists. Such organisms include biota able to survive kilometers below the ocean's surface near hydrothermal vents and microbes that thrive in highly acidic environments.^[33] Characterization of these organisms—their environments and their evolutionary pathways—is considered a crucial component to understanding how life might evolve elsewhere in the universe. Recently, a number of astrobiologists have teamed up with marine biologists and geologists to search for extremophiles and other organisms living around hydrothermal vents on the floors of our own oceans. Scientists hope to use their findings to help them create hypotheses on whether life could potentially exist on certain moons in our own solar system, such as Europa.^[34][35][36]

The origin of life, as distinct from the evolution of life, is another ongoing field of research. Oparin and Haldane postulated that the conditions on the early earth were conducive to the formation of organic compounds from inorganic precursors and thus to the formation of many of the chemicals common to all forms of life we see today. The study of this process, known as prebiotic chemistry, has made some progress, but it is still unclear whether or not life could have formed in such a manner on Earth. The alternative theory of panspermia is that the first elements of life may have formed on another planet with even more favourable conditions (or even in interstellar space, asteroids, etc.) and then have been carried over to Earth by a variety of means.

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Geology

Main article: Geology

The fossil record provides the oldest known evidence for life on Earth.^[37] By examining this evidence, geologists are able to understand better the types of organisms that arose on the early earth. Some regions on Earth, such as the Pilbara in Western Australia and the McMurdo Dry Valleys^[38] of Antarctica, are also considered to be geological analogs to regions of Mars and as such might be able to provide clues to possible Martian life.

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Life in the Solar System

See also: Life on Mars, Life on Europa, and Life on Titan

Europa, due to the ocean that exists under its icy surface, might host some form of microbial life.

The three most likely candidates for life in the solar system (besides Earth) are the planet Mars, the Jovian moon Europa, and Saturn's moon Titan.^{[39][40][41][42][43]} This speculation is primarily based on the fact that (in the cases of Mars and Europa) the planetary bodies may have liquid water, a molecule essential for life as we know it for its use as a solvent in cells.^[44] Water on Mars is found in its polar ice caps, and newly carved gullies recently observed on Mars suggest that liquid water may exist, at least transiently, on the planet's surface,^{[45] [46]} and possibly in subsurface environments such as hydrothermal springs as well. At the Martian temperatures and pressures, such liquid water is likely to be highly saline.^[47] As for Europa, liquid water likely exists beneath the moon's icy outer crust.^[48] This water may be warmed to a liquid state by volcanic vents on the ocean floor (an especially intriguing theory considering the various types of extremophiles that live near Earth's volcanic vents), but the primary source of heat is probably tidal heating.^[49][50]

Another planetary body that could potentially sustain extraterrestrial life is Saturn's largest moon, Titan.^[43] Titan has been described as having conditions similar to those of early Earth; according to bbc.co.uk, "The atmosphere on Titan could be identical to that of the early Earth when life began".^[51] On Titan, scientists have discovered the first liquid lakes outside of Earth, but they are made of ethane and methane, not water.^[52] On March 20, 2008, it was reported that Titan may have an underground ocean of water and ammonia after Cassini data was studied.^[53] Additionally, Saturn's moon Enceladus may have an ocean below its icy surface.^[54]

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Political influence

Please help improve this section by expanding it. Further information might be found on the talk page or at requests for expansion.

In the United States, President George W. Bush's Fiscal Year 2007 NASA Budget cut funding for astrobiological research by 50 percent.^[55] In the 2007 plan, $89 million will be cut from astrobiological research, partly because of a $2.3 billion error in the Space Shuttle Budget.^[56] In a letter to the astrobiological community in the United States, SETI chief executive Thomas Pierson and former NAI director Baruch Blumberg said the following: "Action is needed immediately to prevent the slowing down, or even cessation, of astrobiological research".^[56] Hiroshi Ohmoto, the director of the Astrobiology Research Center in Penn State, said the following in response to the budget cuts to astrobiology:^[56]

Astrobiology is the reason we go into space, to answer fundamental questions about the origins of life and how it evolved, and whether there are other places where organisms are living. It is the whole justification for future space missions.

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Criticisms

Because astrobiology relies mostly on scientific extrapolations over solid, factual evidence, the authenticity of astrobiology as a science can be questioned. While other branches of science remain heavily hypothetical, there is a greater degree of mathematical, pragmatic and/or observational evidence supporting the theories. For example, while science cannot prove string theory, there is a great deal of mathematical computation which implies the existence of strings of energy. Such evidence does not exist with astrobiology, save for an asteroid segment which is believed to have fossilized Martian microbes. Although some have thought a formal degree program in astrobiology unlikely, ^[57] the University of Glamorgan, UK, started just such a degree in 2006.^[58]

Characterization of non-Earth life is extraordinarily unsettled; hypotheses and predictions as to its existence and origin vary wildly; true astrobiological experiments (with modest exceptions such as the study of the ALH84001 meteorite and searches for indications of life in Earthshine) simply cannot occur at present. Finally, astrobiology has been criticized for being unimaginative in the tacit assumption that Earth-like life presents the most likely template for life elsewhere. For example, Michael Crow, the president of Arizona State University, said the following:^[59]

For the last 3,000 years of our science, we really haven't gotten around to the notion that there might be something going on somewhere other than in this small, rural village [called Earth], in this isolated corner of our own galaxy or the Universe itself.

The reference to the universe itself is because our universe may be part of a larger Multiverse where other types of life could exist.

Biologist Jack Cohen and mathematician Ian Stewart, amongst others, consider xenobiology separate from astrobiology for this reason. Cohen and Stewart stipulate that astrobiology is the search for Earth-like life outside of our solar system and say that xenobiologists are concerned with the possibilities open to us once we consider that life need not be carbon-based or oxygen-breathing, so long as it has the defining characteristics of life. See carbon chauvinism.

As with all space exploration, there is the classic argument that there is still a lot more scientists have to learn about Earth. Critics of astrobiology may prefer that federal funding remain dedicated towards searching for unknown species in our own terrestrial biosphere. They feel that Earth is the most plausible and practical region to search for and study life.

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Publications

• The International Journal of Astrobiology, published by Cambridge University Press, is the forum for practitioners in this interdisciplinary field.
• Astrobiology, published by Mary Ann Liebert, Inc., is the leading peer-reviewed international journal created as a forum for scientists seeking to advance our understanding of life's origin, evolution, and distribution in the universe. Astrobiology brings together researchers through the dissemination of original research, hypothesis, education articles, and reviews.
• Grinspoon, David (2003). Lonely planets. The natural philosophy of alien life. New York: ECCO. ISBN 0060185406. 
• Jakosky, Bruce M. (2006). Science, Society, and the Search for Life in the Universe. Tucson: University of Arizona Press. ISBN 0816526133. 
• Lunine, Jonathan I. (2005). Astrobiology. A Multidisciplinary Approach. San Francisco: Pearson Addison-Wesley. ISBN 0805380426. 

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See also

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References

http://www.europlanet-eu.org/index.php?option=com_content&task=view&id=102&I

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External links

At Wikiversity you can learn more and teach others about Astrobiology at:

The Department of Astrobiology

• Astrobiology Instant Expert on New Scientist
• Astrobiology@home
• The Astrobiology Web
• Astrobiology Magazine
• NASA Astrobiology Institute
• Possible Connections Between Interstellar Chemistry and the Origin of Life on the Earth
• Scientists Find Clues That Life Began in Deep Space - NASA Astrobiology Institute
• Stars and Habitable Planets
• Influenza 1918, A Venus Connection?
• NASA-Macquarie University Pilbara Education Project
• Conditions for Life Everywhere
• Snaiad, a world-building project with creatures designed with evolutionary biology in mind.
• Astrobiology Lecture Course Network (a.y. 2005-2006)