This article will be permanently flagged as inappropriate and made unaccessible to everyone. Are you certain this article is inappropriate? Excessive Violence Sexual Content Political / Social
Email Address:
Article Id: WHEBN0000023678 Reproduction Date:
Panspermia (from Greek πᾶν (pan), meaning "all", and σπέρμα (sperma), meaning "seed") is the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids, comets,[1][2] planetoids,[3] and also by spacecraft, in the form of unintended contamination by microbes.[4][5]
Panspermia is a evolution begins. Panspermia is not meant to address how life began, just the method that may cause its distribution in the Universe.[6][7][8]
The first known mention of the term was in the writings of the 5th century BC Greek philosopher Anaxagoras.[9] Panspermia began to assume a more scientific form through the proposals of Jöns Jacob Berzelius (1834),[10] Hermann E. Richter (1865),[11] Kelvin (1871),[12] Hermann von Helmholtz (1879)[13][14] and finally reaching the level of a detailed hypothesis through the efforts of the Swedish chemist Svante Arrhenius (1903).[15]
Fobos-Grunt spacecraft in 2011. Unfortunately, the spacecraft suffered technical difficulties soon after launch and fell back to Earth, so the experiment was never carried out. The experiment would have tested one aspect of panspermia: lithopanspermia, the hypothesis that life could survive space travel, if protected inside rocks blasted by impact off one planet to land on another.[159][160][161][162]
[8][7] Notwithstanding, other scientists think it will be an opportunity to gather evidence for one of panspermia's hypotheses: the possibility of both active and dormant microbes inside comets.[158] In 2014, the
A separate experiment on EXPOSE called Beer was designed to find microbes that could be used in life-support recycling equipment and future "bio-mining" projects on Mars. It carried group of microbes called OU-20 resembling cyanobacteria genus Gloeocapsa, and it survived 553 days exposure outside the ISS.[157]
EXPOSE is a multi-user facility mounted outside the International Space Station dedicated to astrobiology experiments.[140] Results from the orbital mission, especially the experiments SEEDS[152] and LiFE,[153] concluded that after an 18-month exposure, some seeds and lichens (Stichococcus sp. and Acarospora sp., a lichenized fungal genus) may be capable to survive interplanetary travel if sheltered inside comets or rocks from cosmic radiation and UV radiation.[140][154] The survival of some lichen species in space has also been characterized in simulated laboratory experiments.[155][156]
If shielded against solar lithopanspermia hypothesis.[43]
The German EXOSTACK experiment was deployed in 7 April 1984 on board the Long Duration Exposure Facility statellite. 30% of Bacillus subtilis spores survived the nearly 6 years exposure when embedded in salt crystals, whereas 80% survived in the presence of glucose, which stabilize the structure of the cellular macromolecules, especially during vacuum-induced dehydration.[43][151]
BIOPAN is a multi-user experimental facility installed on the external surface of the Russian Foton descent capsule. Experiments developed for BIOPAN are designed to investigate the effect of the space environment on biological material after exposure between 13 to 17 days.[146] The experiments in BIOPAN are exposed to solar and cosmic radiation, the space vacuum and weightlessness, or a selection thereof. Of the 6 missions flown so far on BIOPAN between 1992 and 2007, dozens of experiments were conducted, and some analyzed the likelihood of panspermia. Some bacteria, lichens (Xanthoria elegans, Rhizocarpon geographicum and their mycobiont cultures, the black Antarctic microfungi Cryomyces minteri and Cryomyces antarcticus), spores, and even one animal (tardigrades) were found to have survived the harsh outer space environment and cosmic radiation.[147][148][149][150]
The Exobiology Radiation Assembly (ERA) was a 1992 experiment on board the European Retrievable Carrier (EURECA) on the biological effects of space radiation. EURECA was an unmanned 4.5 tonne satellite with a payload of 15 experiments.[143] It was an astrobiology mission developed by the European Space Agency (ESA). Spores of different strains of Bacillus subtilis and the Escherichia coli plasmid pUC19 were exposed to selected conditions of space (space vacuum and/or defined wavebands and intensities of solar ultraviolet radiation). After the approximately 11 month mission, their responses were studied in terms of survival, mutagenesis in the his (B. subtilis) or lac locus (pUC19), induction of DNA strand breaks, efficiency of DNA repair systems, and the role of external protective agents. The data were compared with those of a simultaneously running ground control experiment:[144][145]
The question of whether certain Gemini IX and XII missions, when samples of bacteriophage T1 and spores of Penicillium roqueforti were exposed to outer space for 16.8 h and 6.5 h, respectively.[43][52] Other basic life sciences research in low Earth orbit started in 1966 with the Soviet biosatellite program Bion and the U.S. Biosatellite program. Thus, the plausibility of panspermia can be evaluated by examining life forms on Earth for their capacity to survive in space.[142] The following experiments carried on low Earth orbit specifically tested some aspects of panspermia or lithopanspermia:
The discovery of deep-sea ecosystems, along with advancements in the fields of astrobiology, observational astronomy and discovery of large varieties of extremophiles, opened up a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats and possible transport of hardy microbial life through vast distances.[52]
Although computer models suggest that a captured meteoroid would typically take some tens of millions of years before collision with a neighboring solar system planet,[32] there are documented viable Earthly bacterial spores that are 40 million years old that are very resistant to radiation,[32][38] and others able to resume life after being dormant for 25 million years,[141] suggesting that lithopanspermia life-transfers are possible via meteorites exceeding 1m in size.[32]
In order to test some these organism's potential resilience in outer space, plant seeds and spores of bacteria, fungi and ferns have been exposed to the harsh space environment.[136][137][140] Spores are produced as part of the normal life cycle of many plants, algae, fungi and some protozoans, and some bacteria produce endospores or cysts during times of stress. These structures may be highly resilient to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation and chemical disinfectants, while metabolically inactive. Spores germinate when favourable conditions are restored after exposure to conditions fatal to the parent organism.
[139] Also, bacteria have been discovered living within warm rock deep in the Earth's crust.[138] It is now known that
revolutionized the study of biology by revealing that terrestrial life need not be Sun-dependent; it only requires water and an energy gradient in order to exist. chemosynthesis, that bubble up from the Earth's interior. This hydrogen sulfide or hydrogen of reactive chemicals, such as oxidation that derives its energy from bacterium It was soon determined that the basis for this food chain is a form of [130].black smokers, scientists discovered colonies of assorted creatures clustered around undersea volcanic features known as Alvin in the deep-sea exploration submersible Galapagos Rift However, in 1977, during an exploratory dive to the [130] Until the 1970s,
[129] A separate fragment of the
Hoyle and Wickramasinghe have speculated that several outbreaks of illnesses on Earth are of extraterrestrial origins, including the 1918 flu pandemic, and certain outbreaks of polio and mad cow disease. For the 1918 flu pandemic they hypothesized that cometary dust brought the virus to Earth simultaneously at multiple locations—a view almost universally dismissed by experts on this pandemic. Hoyle also speculated that HIV came from outer space.[102] After Hoyle's death, The Lancet published a letter to the editor from Wickramasinghe and two of his colleagues,[103] in which they hypothesized that the virus that causes severe acute respiratory syndrome (SARS) could be extraterrestrial in origin and not originated from chickens. The Lancet subsequently published three responses to this letter, showing that the hypothesis was not evidence-based, and casting doubts on the quality of the experiments referenced by Wickramasinghe in his letter.[104][105][106] A 2008 encyclopedia notes that "Like other claims linking terrestrial disease to extraterrestrial pathogens, this proposal was rejected by the greater research community."[102]
It is estimated that space travel over cosmic distances would take an incredibly long time to an outside observer, and with vast amounts of energy required. However, there are reasons to hypothesize that faster-than-light interstellar space travel might be feasible. This has been explored by NASA scientists since at least 1995.[101]
The extrasolar planet results from the Kepler mission estimate 100–400 billion exoplanets, with over 3,500 as candidates or confirmed exoplanets.[97] On 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy.[98][99] 11 billion of these estimated planets may be orbiting sun-like stars.[100] The nearest such planet may be 12 light-years away, according to the scientists.[98][99]
[96]
In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.[95]
In March 2013, a simulation experiment indicate that dipeptides (pairs of amino acids) that can be building blocks of proteins, can be created in interstellar dust.[94]
In 2013, the Atacama Large Millimeter Array (ALMA Project) confirmed that researchers have discovered an important pair of prebiotic molecules in the icy particles in interstellar space (ISM). The chemicals, found in a giant cloud of gas about 25,000 light-years from Earth in ISM, may be a precursor to a key component of DNA and the other may have a role in the formation of an important amino acid. Researchers found a molecule called cyanomethanimine, which produces adenine, one of the four nucleobases that form the “rungs” in the ladder-like structure of DNA. The other molecule, called ethanamine, is thought to play a role in forming alanine, one of the twenty amino acids in the genetic code. Previously, scientists thought such processes took place in the very tenuous gas between the stars. The new discoveries, however, suggest that the chemical formation sequences for these molecules occurred not in gas, but on the surfaces of ice grains in interstellar space.[92] NASA ALMA scientist Anthony Remijan stated that finding these molecules in an interstellar gas cloud means that important building blocks for DNA and amino acids can 'seed' newly formed planets with the chemical precursors for life.[93]
In September 2012, amino acids and nucleotides, the raw materials of proteins and DNA, respectively".[90][91] Further, as a result of these transformations, the PAHs lose their spectroscopic signature which could be one of the reasons "for the lack of PAH detection in interstellar ice grains, particularly the outer regions of cold, dense clouds or the upper molecular layers of protoplanetary disks."[90][91]
[89] On August 2012, and in a world first, astronomers at
On August 2011, a report, based on [84]
In August 2009, NASA scientists identified one of the fundamental chemical building-blocks of life (the amino acid glycine) in a comet for the first time.[80]
[79]C isotopic ratios of organic compounds found in the 13C/12 A 2008 analysis of
Pseudo-panspermia (sometimes called "soft panspermia" or "molecular panspermia") argues that the pre-biotic organic building blocks of life originated in space and were incorporated in the solar nebula from which the planets condensed and were further —and continuously— distributed to planetary surfaces where life then emerged (Chandra Wickramasinghe, who proposed a polymeric composition based on the molecule formaldehyde (CH2O).[74] Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. Usually this occurs when a molecule becomes ionized, often as the result of an interaction with cosmic rays. This positively charged molecule then draws in a nearby reactant by electrostatic attraction of the neutral molecule's electrons. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower.[75] The dust plays a critical role of shielding the molecules from the ionizing effect of ultraviolet radiation emitted by stars.[76]
Further investigations are needed. [71][70][69] in the genetic code which, they believe, is evidence for such a signature.semiotic patterns In 2013 a team of physicists claimed that they had found mathematical and [68][67][66][65] A number of publications since 1979 have proposed the idea that directed panspermia could be demonstrated to be the origin of all life on Earth if a distinctive 'signature' message were found, deliberately implanted into either the
[64] With such materials, and energy from long-lived stars, microscopic life planted by directed panspermia could find an immense future in the galaxy.[63]–N) critically limit nutrition to many terrestrial lifeforms.3 (NOnitrate) and 4 However, the scientists noted that phosphate (PO[63] Directed panspermia to secure and expand life in space is becoming possible due to developments in
Theoretically, unintended panspermia may occur by spacecraft travelling to other celestial bodies. This may concern space researchers who try to prevent contamination. However, directed panspermia may reach a few dozen target systems, leaving billions in the galaxy untouched. In any case, matter is exchanged by meteor impacts in the solar system even without human intervention.
The probability of hitting the target zone can be calculated from P(target) = \frac{A(target)}{\pi (dy)^2} = \frac{a r(target)^2 v^2}{(tp)^2 d^4} where A(target) is the cross-section of the target area, dy is the positional uncertainty at arrival; a - constant (depending on units), r(target) is the radius of the target area; v the velocity of the probe; (tp) the targeting precision (arcsec/yr); and d the distance to the target, guided by high-resolution astrometry of 1×10−5 arcsec/yr (all units in SIU). These calculations show that relatively near target stars(Alpha PsA, Beta Pictoris) can be seeded by milligrams of launched microbes; while seeding the Rho Ophiochus star-forming cloud requires hundreds of kilograms of dispersed capsules.[37]
[62] (30,000 m/s) would reach targets at 10 to 100 light-years in 0.1 million to 1 million years. Fleets of microbial capsules can be aimed at clusters of new stars in star-forming clouds, where they may land on planets or captured by asteroids and comets and later delivered to planets. Payloads may contain c For example, microbial payloads launched by solar sails at speeds up to 0.0001
Conversely, active directed panspermia has been proposed to secure and expand life in space.[37] This may be motivated by biotic ethics that values, and seeks to propagate, the basic patterns of our organic gene/protein life-form.[61] The panbiotic program would seed new solar systems nearby, and clusters of new stars in interstellar clouds. These young targets, where local life would not have formed yet, avoid any interference with local life.
Directed panspermia concerns the deliberate transport of microorganisms in space, sent to Earth to start life here, or sent from Earth to seed new [34] but considering an early "RNA world" Crick noted later that life may have originated on Earth.[59] It has been suggested that 'directed' panspermia was proposed in order to counteract various objections, including the argument that microbes would be inactivated by the space environment and cosmic radiation before they could make a chance encounter with Earth.[60]
Thomas Gold, a professor of astronomy, suggested in 1960 the hypothesis of "Cosmic Garbage", that life on Earth might have originated from a pile of waste products accidentally dumped on Earth long ago by extraterrestrial beings.[58]
Lithopanspermia, the transfer of organisms in rocks from one planet to another either through interplanetary or interstellar space, remains speculative. Although there is no evidence that lithopanspermia has occurred in our own Solar System, the various stages have become amenable to experimental testing.[52]
Based on experimental data on radiation effects and DNA stability, it has been concluded that for such long travel times, boulder sized rocks which are greater than or equal to 1 meter in diameter are required to effectively shield resistant microorganisms, such as bacterial spores against galactic asteroids or comets, the so-called lithopanspermia hypothesis.[43][46]
Then, data gathered by the orbital experiments ERA, BIOPAN, EXOSTACK and EXPOSE, determined that isolated spores, including those of B. subtilis, were killed by several orders of magnitude if exposed to the full space environment for a mere few seconds, but if shielded against solar UV, the spores were capable of surviving in space for up to 6 years while embedded in clay or meteorite powder (artificial meteorites).[43][46] Though minimal protection is required to shelter a spore against UV radiation, exposure to solar UV and cosmic ionizing radiation of unprotected DNA, break it up into its bases.[47][48][49] Also, exposing DNA to the ultrahigh vacuum of space alone is sufficient to cause DNA damage, so the transport of unprotected DNA or RNA during interplanetary flights is extremely unlikely.[49]
In 1903, Svante Arrhenius published in his article The Distribution of Life in Space,[41] the hypothesis now called radiopanspermia, that microscopic forms of life can be propagated in space, driven by the radiation pressure from stars.[42] Arrhenius argued that particles at a critical size below 1.5 μm would be propagated at high speed by radiation pressure of the Sun. However, because its effectiveness decreases with increasing size of the particle, this mechanism holds for very tiny particles only, such as single bacterial spores.[43] The main criticism of radiopanspermia hypothesis came from Shklovskii and Sagan, who pointed out the proofs of the lethal action of space radiations (UV and X-rays) in the cosmos.[44] Regardless of the evidence, Wallis and Wickramasinghe argued in 2004 that the transport of individual bacteria or clumps of bacteria, is overwhelmingly more important than lithopanspermia in terms of numbers of microbes transferred, even accounting for the death rate of unprotected bacteria in transit.[45]
Panspermia can be said to be either interstellar (between [34] or sent from Earth to seed other solar systems have also been proposed.[35][36][37][38] One twist to the hypothesis by engineer Thomas Dehel (2006), proposes that plasmoid magnetic fields ejected from the magnetosphere may move the few spores lifted from the Earth's atmosphere with sufficient speed to cross interstellar space to other systems before the spores can be destroyed.[39][40]
—Stephen Hawking, Origins Symposium, 2009[22]
[21].macroevolution Hoyle and Wickramasinghe further contended that life forms continue to enter the Earth's atmosphere, and may be responsible for epidemic outbreaks, new diseases, and the genetic novelty necessary for [20][19][18]
Planetary habitability, Extraterrestrial life, Universe, Solar System, Saturn
Astrobiology, International Space Station, ExoMars, Evolution, European Space Agency
Russia, Russian language, European Space Agency, Space Shuttle, United States
Astrobiology, Oxygen, Cyanopolyyne, Ichthyothere, Copper
Panspermia, Government of India, Carbon, Chlorine, Hydrogen
Evolution, Panspermia, Astrobiology, Polyyne, Oxygen
Evolution, Oxygen, Universe, Astrobiology, Metabolism
Astrobiology, Expose, Panspermia, Planetary habitability, Extraterrestrial life