Extraterrestrial life

Extraterrestrial life is the term used to define any form of life that may exist and originate outside the planet Earth, the only place in the universe known to support life. Its existence is currently hypothetical; there is yet no evidence of extraterrestrial life that has been widely accepted by the scientific community.

Speculative forms of extraterrestrial life range from humanoid and monstrous beings seen in works of science fiction to life at the much smaller scale of bacteria. Extraterrestrial life forms, especially intelligent ones, are often referred to in popular culture as "aliens" or "ETs." The putative study and theorization of ET life is known as astrobiology (sometimes exobiology), and the term "exopolitics" may be used to denote the study of political relations between humanity and extraterrestrial civilizations.

Historical Belief in Extraterrestrial Life

Astronomy played a significant role in ancient societies, the arrangement of heavenly bodies inspiring cultural beliefs and especially mythology. Beliefs in creatures and lifeforms that populated the sky world became almost common place in the ancient world. The atomists of Greece took up the idea of an infinite universe, with an infinity of populated worlds. The Jewish Talmud states that there are at least 18,000 other worlds. The Babylonians, Egyptians, Sumerians, Chinese and Aztecs all held somewhat similar ideas of multiple worlds that existed amongst the stars. However, these beliefs were often spiritually focused, as the sky and stars was often the domain of deities and supernatural powers. The notion of alien biological lifeforms as they are thought of today, did not take shape for centuries.

Giordano Bruno, De l'Infinito, Univirso e Mondi, 1584

This situation changed, however, with the dramatic shift in thinking initiated by the invention of the telescope and the Copernican assault on geocentric cosmology. Once it became clear that the Earth was merely one planet amongst countless bodies in the universe the extraterrestrial idea moved towards the scientific mainstream. God's omnipotence, it could be argued, not only allowed for other worlds and other life, on some level it necessitated them. The best known early-modern proponent of such ideas was Giordano Bruno, who argued in the 16th century for an infinite universe in which every star is surrounded by its own solar system; he was eventually burned at the stake for heretical ideas. Dominican monk Tommaso Campanella wrote about a Solarian alien race in his Civitas Solis. The possibility of extraterrestrials remained a widespread speculation as scientific discovery accelerated. William Herschel, the discoverer of Uranus, was one of many 18th-19th century astronomers convinced that our Solar System, and perhaps others, would be well populated by alien life. Other luminaries of the period who championed "cosmic pluralism" included Immanuel Kant and Benjamin Franklin. At the height of the Enlightenment even the Sun and Moon were considered candidates for hosting aliens.

Extraterrestrials and the Modern era

This enthusiasm towards the possibility of alien life continued well into the 20th century. As long as human kind was unable to travel into space, extraterrestrial life seemed as probable to scientists and the general public alike. However, a split in the belief in E.T. life forms occurred in the beginning half of the 20th century. With advancement in the scientific areas of physics, astronomy and evolutionary biology, scientists started to understand how complicated and fragile it was for life to develop on Earth, let alone elsewhere in a largely dangerous and inhospitable universe. Furthermore, the early explorations of space by probes showed no signs of life on the barren planet of Mars and exposed Venus to be a planet of such dramatic climate it is not conducive to support any known forms of life. The major scientific argument against extraterrestrial life was formed; Earth was unique in its evolution, randomly composed of the exact conditions to support the fragile, and somewhat random itself, process that led to life. Most scientists believed, and still do that for such conditions to happen twice, even in a universe as big as ours, is unlikely (See Scientific Approach below).

UFOs and Reported Abductions

Yet, as science was dismissing the notion of extraterrestrial life, it was becoming more popular in the public's imagination. The connection between extraterrestrials, the sudden frequent reports of UFOs, and the anthropomorphizing of extraterrestrials into the common identity of aliens, as they are known today, happened in a time period between 1920 and 1950. The possibility of intelligent life forms became an almost alluring mystery to the public. Early science fiction of the period used aliens frequently in its stories. Even those who claimed not to believe in aliens, shared a widespread fear of malevolent creatures from space, possibly best demonstrated by Orson Welles' infamous radio broadcast of The World of the Wars in which hundreds of people in the New York and New Jersey area were led to believe an invasion by aliens was taking place.

Artistic depiction of a Grey Alien

Belief in aliens has become one of the most interesting and complicated aspects of pop culture, the paranormal and the new age movement in the later half of the 20th century. Not only is commonly believed that UFOs are in fact alien space craft, but reports of contact between humans and aliens have been prevalent since the 1950s. One popular phenomenon is the abduction of humans by aliens, during which humans are unwittingly brought aboard space craft and subjected to medical examinations. Conspiracy theorists have claimed that world governments have clandestine relationships with aliens or are otherwise covering up alien existence. Some new age societies believe aliens hold a special place in the spiritual realm. These beliefs are fueled by overwhelming reports, observations, and the media, in which aliens are commonplace elements of movies and television shows, as well as books and documentaries. Commonly, these aliens are seen as small, with grayish skin, large head and black, lidless eyes. They are sometimes referred to as Greys. Other depictions perceive aliens as reptilian, insect-like, or even resembling people of Nordic descent.

File:Grey alien close1.jpg

A grey alien close-up

Aliens are depicted in numerous different ways; some portray and believe aliens exist to help mankind, while other times aliens are seen as hostile and using mankind for their own advancement. Either way, the notion that there are other life forms that possess similar intelligence and cognizant abilities as humans seems to strike a cord in humanity. Perhaps it is an overactive imagination projecting onto the infinity of the cosmos, of which we still know little. Or perhaps the fear of the ultimate unknown, that which is alien to mankind that helps fuel the belief.

Scientific Approach

Since there is no solid proof for the existence of extraterrestrial life, most of the scientific community since the mid 20th century have not given the idea much thought, especially with the stigma of the more outlandish pop culture perspectives on the matter. However, there have been, and continue to be, scientists who engage the idea, on many different levels.

Basis of Life

In order for something to be considered a living organism, there are five biological criteria that must be met: ability to reproduce and grow, it consume nutrients in order to survive, have mobility and respond to external stimuli. Further, all living organisms on earth are based on the element carbon, depend on water as a medium for crucial chemical reactions, and are made up of long strands of amino acids, known as DNA — Deoxyribonucleic acid. The difficulty with trying to understand possible other life forms, is that science currently is unaware of any other composition of life (there has been some speculation that instead of carbon, the element silicon may constitute the basis of extraterrestrial life). Therefore, either life in the universe can only exist on planets with similar water and carbon levels and temperature of Earth, or life exists in some form that we currently do not know about, and raises the issue of how to look for something that does not correspond to current understandings.

Speculation

File:Exoplanet Plants.jpg

Pigments other than green might dominate plant life on exoplanets

Without concrete facts to analyze or direct phenomena to observe, most scientists studying extraterrestrial life must do so by speculation (Most speculation is, however, based on what is accepted knowledge of astronomy and biology, as well as careful scientific postulating). Even with so many unknown variables, such postulating requires that specific guidelines be established in order to further pursue the notion. For example, scientists must first try to understand if the evolution of extraterrestrial life would have occurred independently in different places in the universe, or if, as a minority of scientists contend, life in the universe could have stemmed from a smaller number of points of origin, and then spread across the universe, from habitable planet to habitable planet, known as panspermia.

Another concern is the evolutionary state of extraterrestrial life. There seems to be a greater possibility in the mind of many scientists that simple life forms, such as basic proteins and microbes, are more probable than more radically evolved organisms. One reason for this is that these simpler lifeforms are easier to develop and maintain than a more complicated life form, such as man, and therefore can possibly exist on a wider variety of environments. The other reasoning for simpler life forms does not disclude the notion of complex lifeforms, but rather that mankind will never find any, because by the time a probe or space craft could reach other planets, the stars supporting the alien species would have died out and destroyed them. In this scenario, the most likely organisms we will discover are simple proteins in our own solar system.

The assumption of radical diversity amongst putative extraterrestrials is by no means settled. While many exobiologists do stress that the enormously heterogeneous nature of Earth life foregrounds even greater variety in space, others point out that convergent evolution dictates substantial similarities between Earth and off-Earth life. These two schools of thought are called "divergionism" and "convergionism," respectively.

Currently, Astrobiology is a field of study that has gained legitimacy and acceptance in the scientific community. Its main objectives include the search for extraterrestrial life, but in doing so seek to develop a better understanding of life on Earth

The Search For Extraterrestrials

Since the last quarter of the 20th century, scientists have been actively searching the universe for other lifeforms with all the different types of technology available. Yet, even if all of NASA and the The European Space Agency's budgets were directed towards this one goal, the universe is still too large and our technological means still not adequate enough to exhaustively search those areas in space that we know are possibly harboring life. Still, there are undaunted scientists who continue to search for possible life, whether it be bacteria or advanced civilizations. There are two different methods scientists use in this search: the direct and indirect method.

The Direct Method

Scientists are directly searching for evidence of unicellular life within the solar system, carrying out studies on the surface of Mars, Europa, one of Jupiter's moons, and Titan, a moon of Saturn. The possibility of life on Mars has always been a matter of speculation, but became an even more heated issue in 1996, when structures resembling bacteria were reportedly discovered in a meteorite, ALH84001, thought to be formed of rock ejected from Mars. Scientists are still debating the evidence, but the possibility is enough to spur further searches. NASA's recent Mars lander probes have been surveying the landscape of the red planet, analyzing the geological and chemical makeup of the environment, in order to determine, among other things, if the planet could have at some point supported life. There is circumstantial evidence that Mars was at one time supportive of life; the frozen water at Mars poles most likely once flowed over the surface of the planet, and the levels of methane in the atmosphere, a gas that occurs in Earth's atmosphere as the result of biological processes. As martian experiments continue to become more common place, some answers as to the question of life may be discovered, but for the moment life on Mars is an open ended question.

Recent studies of Saturn's moon Titan have discovered high levels of methane and nitrogen in the atmosphere, along with other organic compounds that point to the possibility of life forms. Its extremely low temperatures (-289 Fahrenheit) and hostile weather more than likely rule out current life, at least one the surface. Underground liquid reservoirs, coupled with recent discoveries on Earth of small life forms surviving in incredibly harsh environments, suggests that perhaps there are, or were, micro-sized organisms on Titan. Further studies will focus on answering this question.

Terrestrial Planet Finder - Infrared interferometer concept of finding Earth-like extrasolar planets

Astronomers are also searching for extrasolar planets that would be conducive to life, especially those like OGLE-2005-BLG-390Lb which have been found to have Earth-like qualities. Current radiodetection methods have been inadequate for such a search, as the resolution afforded by recent technology is inadequate for detailed study of extrasolar planetary objects. Future telescopes should be able to image planets around nearby stars, which may reveal the presence of life (either directly or through spectrography which would reveal key information such as the presence of free oxygen in a planet's atmosphere). Darwin is an ESA mission designed to find Earth-like planets, and analyze their atmosphere. It has been argued that one of the best candidates for the discovery of life-supporting planets may be Alpha Centauri, the closest star system to Earth, given that two of the three stars in the system are broadly sun-like.

Indirect search

Some scientists theorize that any technological society in space will be transmitting information over the medium of space, and that instruments on Earth could possibly pick up those transmissions. In 1960, Cornell University astronomer Frank Drake performed the first modern experiment, based on this theory, named "Project Ozma," after the Queen of Oz in L. Frank Baum's fantasy books. Drake used a 25-meter-diameter radio telescope at Green Bank, West Virginia, to examine the stars Tau Ceti and Epsilon Eridani near the 1.420 gigahertz marker frequency. Although nothing of great interest was discovered, the notion spawned other searches that continue to this day. Such searches had been categorized under the acronym SETI (pronounced ['sɛti]) Search for Extra-Terrestrial Intelligence; Using radio telescopes to scan for cosmic transmissions is an approach widely endorsed by the scientific community as hard science.

There are great challenges in searching across the sky to detect a first transmission that can be characterized as intelligent, since its direction, spectrum and method of communication are all unknown beforehand. SETI projects necessarily make assumptions to narrow the search, and thus no exhaustive search has so far been conducted. A basic assumption of SETI is that of "Mediocrity": the idea that humanity is not exotic in the cosmos but in a sense "typical" or "medium" when compared with other intelligent species.^{[citation needed]} This would mean that humanity has sufficient similarities with other intelligent beings that communications would be mutually desirable and understandable. If this basic assumption of Mediocrity is correct, and other intelligent species are present in any number in the galaxy at our technological level or above, then communications between the two worlds should be inevitable.

Another assumption is to focus on Sun-like stars. Very big stars have relatively short lifetimes, meaning that intelligent life would likely not have time to evolve on planets orbiting them. Very small stars provide so little heat and warmth that only planets in very close orbits around them would not be frozen solid, and in such close orbits these planets would be tidally locked to the star, with one side of the planet perpetually baked and the other perpetually frozen. (However, some speculate that a thick cloud cover may mitigate these differences.

About 10% of the stars in the Milky Way galaxy are Sun-like, and there are about a thousand such stars within 100 light-years of the Sun. These stars would be useful primary targets for interstellar listening. In order to find an electromagnetic transmission from an alien civilization we also have to search through most of the useful radio spectrum, as there is no way to know what frequencies aliens might be using. Trying to transmit a powerful signal over a wide range of wavelengths is impractical, and so it is likely that such a signal would be transmitted on a relatively narrow band. This means that a wide range of frequencies must be searched at every spatial coordinate of the sky.

There is also the problem of knowing what to listen for, as we have no idea how a signal sent by aliens might be modulated, and how the data transmitted by it might be encoded. Narrow-bandwidth signals that are stronger than background noise and constant in intensity are obviously interesting, and if they have a regular and complex pulse pattern are likely to be artificial.

However, while studies have been performed on how to send a signal that could be easily deciphered, there is no way to know if the assumptions of those studies are valid, and deciphering the information from an alien signal could be very difficult.

Many different SETI projects have come and gone since the mid-twentieth century. The massive radio dish in Arecibo, Puerto Rico, once was distinguished in its SETI program, until the U.S. government cut its funding. Since then, most of the SETI work being done has been in the private sector. Currently, there are several operating projects, such as the Allen Telescope Array in California, the Phoenix Project in Australia and Harvard's OPTICAL SETI project

Arecibo message

The Arecibo message is a digital message sent to globular star cluster M13, and is a well-known symbol of human attempts to contact extraterrestrials.

In 1974, a largely symbolic attempt was made to send a message to other worlds. To celebrate a substantial upgrading of the 305 meter Arecibo Radio Telescope in Puerto Rico, a coded message of 1,679 bits was transmitted towards the Globular Cluster M13, about 25,100 light years away.

The pattern of 0s and 1s contained in the message defines a 23 × 73 two dimensional grid which when plotted reveals some data about our location in the Solar System, a stylized figure of a human being, chemical formula and an outline of the radio telescope itself. The 23 by 73 grid was chosen because both 23 and 73 are prime numbers, which makes it easier to decode the message.

Given the limitations of the speed of light for message transmission, no reply would be possible before the year 52,174 (approximately) and hence has been dismissed by some as a publicity stunt. A controversy arose because the transmission raised the serious question of whether a small group should be allowed to speak for Earth.

References

ISBN links support NWE through referral fees

• Exers, Ronald, D. Cullers, J. Billingham, L. Scheffer (editors) (2003). SETI 2020: A Roadmap for the Search for Extraterrestrial Intelligence. SETI Press. ISBN 0-9666335-3-9. 
• McConnell, Brian and Chuck Toporek (2001). Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations. O'Reilly. ISBN 0-596-00037-5. 
• Roth, Christopher F., "Ufology as Anthropology: Race, Extraterrestrials, and the Occult." In E.T. Culture: Anthropology in Outerspaces, ed. by Debbora Battaglia. Durham, N.C.: Duke University Press, 2005.
• Sagan, Carl. 1996. The Demon-Haunted World: Science as a Candle in the Dark: chapter 4: "Aliens"
• David Grinspoon (2003). Lonely Planets: The Natural Philosophy of Alien Life. HarperCollins. ISBN 0-06-018540-6. 
• Jack Cohen and Ian Stewart (2002). Evolving the Alien: The Science of Extraterrestrial Life. Ebury Press. ISBN 0-09-187927-2. 
• John C. Baird (1987). The Inner Limits of Outer Space: A Psychologist Critiques Our Efforts to Communicate With Extraterrestrial Beings. Hanover: University Press of New England. ISBN 0-87451-406-1. 
• Donald Goldsmith (1997). The Hunt for Life on Mars. New York: A Dutton Book. ISBN 0-525-94336-6. 
• Michael T. Lemnick (1998). Other Worlds: The Search for Life in the Universe. New York: A Touchstone Book. 
• Cliff Pickover (2003). The Science of Aliens. New York: Basic Books. ISBN 0-465-07315-8. 
• Roth, Christopher F. (2005) "Ufology as Anthropology: Race, Extraterrestrials, and the Occult." In E.T. Culture: Anthropology in Outerspaces, ed. by Debbora Battaglia. Durham, N.C.: Duke University Press.
• Crowe, Michael J.. The Extraterrestrial Life Debate, 1750—1900. Dover Publications. 
• Sagan, Carl and I.S. Shklovskii (1966). Intelligent Life in the Universe. Random House. 
• Sagan, Carl (1973). Communication with Extraterrestrial Intelligence. MIT Press. 

External links

• NASA: Astrobiology Retrieved May 16, 2007.
• PBS: Life Beyond Earth a film by Timothy Ferris Retrieved May 16, 2007.
• PBS: Exploring Space - The Quest for Life by Scott Pearson Retrieved May 16, 2007.
• Xenopsychology by Robert A. Freitas Jr. Retrieved May 16, 2007.
• "What Aliens Might Look Like" from National Geographic Magazine Retrieved May 16, 2007.
• Top stars picked in alien search Retrieved May 16, 2007.
• SETI Institute Retrieved May 16, 2007.
• SETI: Searching for Life – Article series in Sky & Telescope magazine. Retrieved May 16, 2007.
• Cirkovic, Milan M., and Bradbury, R. J., 200n, "Galactic Gradients, Postbiological Evolution, and the Apparent Failure of SETI." Retrieved May 16, 2007.
• Searching for Good Science: The Cancellation of NASA's SETI Program (PDF) – By Stephen J. Garber, NASA History Office. Journal of the British Interplanetary Society, Vol. 52, pp. 3-12, 1999. Provides more details on the elimination of SETI funding by the US Congress in 1993. Retrieved May 16, 2007.

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