Panspermia
Panspermia panspermia (from the ancient Greek πᾶν (bread) 'all' and σπέρμα (sperm) 'seed'), is the hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids, and also by spacecraft carrying non-contamination intentional by microorganisms. The distribution may have occurred spanning galaxies and therefore may not be restricted to the limited scale of solar systems.
Although the presence of life is currently confirmed only on Earth, some scientists think that extraterrestrial life is not only plausible, but probable or inevitable. Space probes and instruments have begun to examine other planets and moons in the Solar System and in other planetary systems, looking for evidence of a past or active pathway, and projects like SETI attempt to detect radio transmissions from possible extraterrestrial civilizations.
The concept of Panspermia should not be confused with the concept of Alien Creationism, in which the direct intervention of an extraterrestrial civilization in the process is postulated.
Definition
The term "panspermia" was championed by the German biologist Hermann Richter in 1865. In 1908, the Swedish chemist Svante August Arrhenius used the word to explain the beginning of life on Earth. Astronomer Fred Hoyle also supported that hypothesis. It was not until the Nobel Prize in Chemistry was awarded to Svante Arrhenius that he popularized the concept that life had originated in outer space.
Hypothesis
The panspermia hypothesis proposes, for example, that microscopic life forms that can survive the effects of space (such as extremophiles) can become trapped in debris ejected into space after collisions between planets and small bodies in the Earth. Solar System that support life. Some organisms can travel inactive for an extended period of time before randomly colliding with other planets or mingling with protoplanetary disks. Under certain ideal impact circumstances (in a body of water, for example) and under ideal conditions on planetary surfaces, it is possible for surviving organisms to become active and begin to colonize their new environment. At least one report finds that the endospores of a type of Bacillus bacteria found in Morocco can survive heating to 420°C (788°F), making the case for panspermia even stronger. The study of panspermia do not focus on how life began, but on the methods that can distribute it in the Universe.
Molecular panspermia
A less controversial variation of this Hypothesis called "molecular panspermia" or "soft panspermia", argues that only the components Prebiotic organics of life originated in space, were incorporated into the solar nebula from which the planets condensed, and were further and continuously distributed to planetary surfaces where life later emerged (abiogenesis). From early Beginning in the 1970s, it became apparent that interstellar dust included a large component of organic molecules. Interstellar molecules are formed by chemical reactions within widely dispersed interstellar or circumstellar clouds of dust and gas. Dust plays a critical role in shielding molecules from the ionizing effect of ultraviolet radiation emitted by stars.
The chemistry that led to life may have started shortly after the Big Bang, 13.8 billion years ago, during a time when the Universe was only 10 to 17 million years old.
History
The first known mention of the term was in the writings of the Greek philosopher Anaxagoras in the 5th century BC. C. Panspermia began to assume a more scientific form through the proposals of Jöns Jacob Berzelius (1834), Hermann E. Richter (1865), Kelvin (1871), Hermann von Helmholtz (1879) and finally reaching the level of a detailed scientific hypothesis through the efforts of the Swedish chemist Svante Arrhenius (1903).
Fred Hoyle (1915-2001) and Chandra Wickramasinghe (1939) were influential proponents of panspermia. In 1974 they hypothesized that some dust in interstellar space was largely organic (containing carbon), which which Wickramasinghe later proved to be correct. Hoyle and Wickramasinghe further argued that life forms continue to enter Earth's atmosphere and may be responsible for outbreaks of epidemics, new diseases, and the genetic novelty necessary for macroevolution.
In a presentation at the Origins Symposium on April 7, 2009, physicist Stephen Hawking expressed his views on what humans may encounter when venturing into space, such as the possibility of extraterrestrial life through the theory of panspermia.: "Life could spread from planet to planet or from star system to star system, carried by meteors".
Three series of astrobiology experiments outside the International Space Station have been conducted between 2008 and 2015 (EXPOSE), where a wide variety of biomolecules, microorganisms, and their spores were exposed to the solar flux and vacuum of space for approximately 1,5 years. Some organisms survived in an inactive state for considerable periods of time, and those samples protected by simulated meteorite material provide experimental evidence for the likelihood of the hypothetical lithopanspermia scenario.
Various simulations in laboratories and in low-Earth orbit suggest that ejection, inflow, and impact can survive for some simple organisms. In 2015, traces of biotic material were found in 4.1 billion-year-old rocks in Western Australia, when the young Earth was about 400 million years old. According to one researcher, "if life arose relatively quickly on Earth... then it could be common in the universe".
In April 2018, a Russian team published a paper revealing that they found DNA on the ISS exterior from terrestrial and marine bacteria similar to those previously observed in surface microlayers in coastal areas of the Barents and Kara Seas. They conclude: "The presence of DNA from wild terrestrial and marine bacteria on the ISS suggests their possible transfer from the stratosphere to the ionosphere with the ascending branch of the global atmospheric electrical circuit. Alternatively, terrestrial, marine and wild bacteria may have an ultimate spatial origin".
In October 2018, Harvard astronomers presented an analytical model that suggests matter, and potentially dormant spores, can be exchanged across the vast distances between galaxies, a process dubbed 'galactic panspermia' #39;, and not restricted to the limited scale of solar systems. The detection of an extrasolar object called 'Oumuamua crossing the inner Solar System in a hyperbolic orbit confirms the existence of a continuous material link with exoplanetary systems.
In November 2019, scientists reported detecting, for the first time, sugar molecules, including ribose, in meteorites, suggesting that chemical processes on asteroids may produce some bioingredients fundamentally essential for life and support the notion of an RNA world before a DNA-based origin of life on Earth, and possibly also the notion of panspermia.
Proposed mechanisms
Panspermia can be said to be interstellar (star systems) or interplanetary (between planets in the same star system); its transport mechanisms may include comets, radiation pressure, and lithopanspermia (microorganisms embedded in rocks). Interplanetary transfer of non-living material is well documented, as evidenced by meteorites of Martian origin found on Earth. Space probes may also be a viable transport mechanism for interplanetary cross-pollination into the Solar System or even beyond. However, space agencies have implemented planetary protection procedures to reduce the risk of contamination, although, as recently discovered, some microorganisms, such as Tersicoccus phoenicis, may be resistant to procedures used in clean assembly room facilities. spaceships.
In 2012, mathematician Edward Belbruno and astronomers Amaya Moro-Martín and Renu Malhotra proposed that gravitational transfer of low-energy rocks between young planets of stars in their birth cluster is common rather than rare in the population general galactic stellar formation. Panspermia deliberately directed from space to seed Earth or sent from Earth to seed other planetary systems has also been proposed. A twist on the hypothesis by engineer Thomas Dehel (2006), proposes that the fields Magnetic plasmoids ejected from the magnetosphere can move the few spores lifted from Earth's atmosphere with sufficient velocity to cross interstellar space to other systems before the spores can be destroyed. In 2020, paleobiologist Grzegorz Sadlok proposed the hypothesis that life can travel interstellar distances on nomadic exoplanets and/or exomoons.
Radiopanspermia
In 1903, Svante Arrhenius published in his article The distribution of life in space, the hypothesis now called radiopanspermia, that microscopic forms of life can be propagated in space, driven by radiation pressure from stars. Arrhenius argued that particles of a critical size below 1.5 μm would be propagated at high speed by radiation pressure from the Sun. However, because their efficiency decreases by increasing particle size, this mechanism applies only to very small particles, such as individual bacterial spores.
The main criticism of the radiopanspermia hypothesis came from Iosif Shklovsky and Carl Sagan, who pointed to the evidence for the lethal action of space radiation (UV and X-rays) in the cosmos. Regardless of the evidence, Wallis and Wickramasinghe argued in 2004 that the transport of individual bacteria or groups of bacteria is overwhelmingly more important than lithopanspermia in terms of the number of microbes transferred, even allowing for the rate of death of unprotected bacteria in transit.
Then, data collected by the ERA, BIOPAN EXOSTACK, and EXPOSE orbital experiments determined that isolated spores, including those of B. subtilis, died if exposed to the full space environment for only a few seconds, but if shielded from solar UV rays, the spores were capable of surviving in space for up to six years while embedded in clay or meteorite dust. (artificial meteorites).
Minimal shielding is required to protect a spore against ultraviolet radiation: exposure of unprotected DNA to solar ultraviolet rays and cosmic ionizing radiation breaks it down into its constituent bases. Additionally, exposing DNA to ultrahigh vacuum of space alone is enough to cause DNA damage, so transport of unprotected DNA or RNA during interplanetary flights powered only by slight pressure is extremely unlikely.
The feasibility of other means of transport for the more massive armored spores to the outer Solar System, for example through gravitational capture by comets, is unknown at this time.
Based on experimental data on the effects of radiation and DNA stability, it has been concluded that for such long travel times, boulder-sized rocks that are greater than or equal to 1 m in diameter are required to effectively shield resistant microorganisms such as bacterial spores against galactic cosmic radiation. These results clearly deny the hypothesis of radiopanspermia, which requires single spores accelerated by radiation pressure from the Sun, plus many years to travel between planets., and support the probability of interplanetary transfer of microorganisms within asteroids or comets, the so-called lithopanspermia hypothesis.
Litopanspermia
Lihopanspermia, which speaks of the transfer of organisms in rocks from one planet to another through interplanetary or interstellar space, remains speculative. Although there is no evidence that lithopanspermia has occurred in the Solar System, the various stages have become amenable to experimental evidence.
Planetary ejection
for lithopanspermia to occur, researchers have suggested that microorganisms must survive ejection from a planetary surface involving extreme forces of acceleration and shock with associated temperature variations. Hypothesized values of shock pressures experienced by ejected rocks are obtained with Martian meteorites, suggesting shock pressures of about 5 to 55 GPa, acceleration of 3 Mm/s2, and jerk of 6 Gm/s3 and post-shock temperature increases of approximately 1 K to 1000 K. To determine the effect of acceleration during ejection on microorganisms, rifle and ultracentrifuge methods were successfully used. under simulated outer space conditions.
Survival in transit
The survival of microorganisms has been studied extensively using simulated facilities and in low-Earth orbit. A large number of microorganisms have been selected for challenge experiments. It is possible to separate these microorganisms into two groups, those of human origin and extremophiles. The study of human-borne microorganisms is important for human well-being and future manned missions; while extremophiles are vital for studying the physiological requirements for survival in space.
Atmospheric entry
An important aspect of the lithopanspermia hypothesis to test is that microbes on or in rocks could survive hypervelocity entry from space through Earth's atmosphere (Cockell, 2008). As with planetary ejection, this is manageable experimentally, with sounding rockets and orbiters being used for microbiological experiments. B. subtilis inoculated into granite domes were subjected to hypervelocity atmospheric transit (twice) by launch at an altitude of ∼120 km on an Argentinian Orion II two-stage rocket. The spores were shown to have survived on the sides of the rock, but did not survive on the forward facing surface which was subjected to a maximum temperature of 145°C.
The exogenous arrival of photosynthetic microorganisms could have quite profound consequences for the course of biological evolution on the inoculated planet. Since photosynthetic organisms must be close to the surface of a rock to gain sufficient light energy, atmospheric transit could act as a filter against them by ablating the surface layers of the rock. Although cyanobacteria have been shown to survive the drying and freezing conditions of space in orbital experiments, this would not be beneficial as the STONE experiment demonstrated that they cannot survive atmospheric entry. Therefore, non-photosynthetic organisms in the depths of the rocks have the possibility of surviving the process of entry and exit. Research presented at the European Planetary Science Congress in 2015 suggests that ejection, inflow, and impact can survive for some simple organisms.
Accidental panspermia
Thomas Gold, a professor of astronomy, suggested the "cosmic garbage' hypothesis in 1960, explaining that life on Earth could have originated accidentally from a pile of waste products dumped on the Earth. Earth long ago by extraterrestrial beings.
Directed panspermia
Directed panspermia refers to the deliberate transport of microorganisms into space, sent to Earth to start life here, or sent from Earth to seed new planetary systems with life by introduced species of microorganisms on nonliving planets. Nobel Prize winner Francis Crick, along with Leslie Orgel, proposed that life may have been spread intentionally by an advanced extraterrestrial civilization, but considering an "RNA world" early, Crick later pointed out that life may have originated on Earth. It has been suggested that "directed" panspermia was proposed; to counter various objections, including the argument that microbes would be inactivated by the space environment and cosmic radiation before they could have a chance encounter with Earth.
In contrast, directed active panspermia has been proposed to ensure and extend life in space. This may be motivated by a biotic ethic that values, and seeks to propagate, the basic patterns of our organic way of life of genes/proteins. The panbiotic program would seed new nearby planetary systems and new star clusters in interstellar clouds. These young stars, where local life has not yet formed, avoid any interference.
For example, microbial payloads launched by solar sails at speeds up to 0.0001c (30,000 m/s) would hit targets 10 to 100 light years in 0.1 million yr 1 million years. Fleets of microbial capsules can target clusters of new stars in star-forming clouds, where they can land on planets or be captured by asteroids and comets and then delivered to the planets. Payloads can contain extremophiles for various environments and cyanobacteria similar to the early microorganisms. Resistant multicellular organisms (rotifer cysts) can be included to induce further evolution.
The probability of hitting the target area can be calculated from where A (target) is the cross section of the target area, dy is the positional uncertainty at the arrival; a-constant (depending on units), r (target) is the radius of the target area; v the velocity of the probe; (tp) targeting precision (parcsec/year); and d the distance to the target, guided by high-resolution astrometry of 1×10-5 seconds of arc/year (all units in SIU). These calculations show that relatively close target stars (Alpha PsA, Beta Pictoris) can be seeded per milligram of released microbes; while seeding the Rho Ophiochus star-forming cloud requires hundreds of kilograms of scattered capsules.
Directed panspermia to ensure and expand life in space is becoming possible due to developments in solar sails, precise astrometry, extrasolar planets, extremophiles, and microbial genetic engineering. After determining the composition of the chosen meteorites, astroecologists have conducted laboratory experiments that suggest that many colonizing microorganisms and some plants may obtain much of their chemical nutrients from materials from asteroids and comets. However, scientists noted that phosphate (PO4) and nitrate (NO3–N) critically limit nutrition to many terrestrial life forms. With these materials and energy from long-lived stars, microscopic life planted by directed panspermia could find a vast future in the galaxy.
Several publications since 1979 have advanced the idea that directed panspermia could be shown to be the origin of all life on Earth if a distinctive 'signature' message were found, deliberately implanted in the brain. genome or in the genetic code of the first microorganisms by our hypothetical progenitor.
In 2013, a team of physicists claimed they had found mathematical and semiotic patterns in the genetic code which they believe to be evidence of such a signature. This claim has been disputed by biologist PZ Myers, who said, writing in Pharyngula:
Unfortunately, what you have described so honestly is honest rubbish... Their methods failed to recognize a functional association known in the genetic code; they did not rule out the operation of natural law before rushing to falsely infer the design... We certainly don't need to invoke panspermia. Nothing in the genetic code requires design. and the authors have not proved otherwise.
In a subsequent peer-reviewed article, the authors address the workings of natural law in an extensive statistical test and come to the same conclusion as in the previous article. Methodological concerns raised by PZ are also addressed in special sections Myers and a few others.
Pseudopanspermia
Pseudopanspermia (sometimes called soft panspermia, molecular panspermia, or quasi-panspermia) proposes that the organic molecules used for life originated in space and were incorporated into the solar nebula, from which the planets condensed and they were distributed more and more continuously to the surfaces of the planets, where life later emerged (abiogenesis). Since the early 1970s it became clear that interstellar dust consisted of a large component of organic molecules. The first suggestion came from Chandra Wickramasinghe, who proposed a polymer composition based on the formaldehyde molecule (CH2O).
Interstellar molecules are formed by chemical reactions within widely dispersed interstellar or circumstellar clouds of dust and gas. Typically, this occurs when a molecule becomes ionized, often as a result of an interaction with cosmic rays. This positively charged molecule then attracts a nearby reactant by electrostatic attraction of the electrons from the neutral molecule. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower. Dust plays a fundamental role in shielding molecules from the ionizing effect of ultraviolet radiation emitted by stars. Mathematician Jason Guillory, in his 2008 analysis of the 12C/13C isotopic ratios of organic compounds found in the Murchison meteorite, points to a non-terrestrial origin of these molecules rather than terrestrial contamination. Biologically relevant molecules identified so far include uracil (an RNA nucleobase) and xanthine. These results demonstrate that many organic compounds that are components of life on Earth were already present in the early Solar System and may have played key roles. at the origin of life.
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.
In August 2011, a report was released, based on NASA studies of meteorites found on Earth, suggesting that the building blocks of DNA (adenine, guanine, and related organic molecules) may have formed extraterrestrially on Earth. outer space. In October 2011, scientists reported that cosmic dust contains complex organic matter ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally and rapidly by stars. the scientists suggested that these complex organic compounds may have been linked to the development of life on Earth and said: "If this is the case, life on Earth may have had an easier start, as these organic products can serve as basic ingredients for life".
In August 2012, and for the first time in the world, astronomers at the University of Copenhagen reported the detection of a specific sugar molecule, glycolaldehyde, in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422, which lies 400 light-years from Earth. Glycolaldehyde is needed to form ribonucleic acid, or RNA, which has a similar function to DNA. This finding suggests that complex organic molecules may form in star systems before the formation of planets, and will eventually reach young planets early in their formation.
In September 2012, NASA scientists reported that polycyclic aromatic hydrocarbons (PAHs), under the conditions of the interstellar medium (ISM), are transformed, through hydrogenation, oxygenation, and hydroxylation, into more complex organic compounds: "a step on the way to amino acids and nucleotides, the raw materials of proteins and DNA, respectively". Also, as a result of these transformations, PAHs lose their spectroscopic signature, which could be one of the reasons "for the lack of detection of PAHs in interstellar ice grains, particularly in the outer regions of cold, dense clouds or in the upper molecular layers of protoplanetary disks".
In 2013, the Atacama Large Millimeter Array (ALMA Project) confirmed that researchers have discovered an important pair of prebiotic molecules in the icy particles of interstellar space (ISM). The chemicals, found in a giant cloud of gas some 25,000 light-years from Earth in ISM, may be one precursor to a key component of DNA and the other may have a role in the formation of an important amino acid. The researchers found a molecule called cyanomethanimine, which produces adenine, one of the four nucleobases that make up the "stepping stones" of the brain. in the ladder-shaped structure of DNA.
The other molecule, called ethanamine, is thought to play a role in the formation of alanine, one of the twenty amino acids in the genetic code. Previously, scientists thought that such processes took place in the very tenuous gas between stars. However, the new discoveries suggest that the chemical formation sequences of these molecules did not occur in gas, but on the surfaces of ice grains in interstellar space. NASA scientist Anthony Remijan stated that finding these molecules in a cloud of interstellar gas means that important building blocks for DNA and amino acids can "seed" the next generation. newly formed planets with the chemical precursors for life.
In March 2013, a simulation experiment indicated that dipeptides (pairs of amino acids) can be created in interstellar dust that can be building blocks of proteins.
In February 2014, NASA announced a greatly improved 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 appear to have formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.
In March 2015, NASA scientists reported that, for the first time, complex organic compounds of life's DNA and RNA, including uracil, cytosine, and thymine, have formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the Universe, may have formed in red giants or in interstellar dust and gas clouds, according to scientists.
In May 2016, the Rosetta Mission team reported the presence of glycine, methylamine, and ethylamine in 67P/ Churyumov-Gerasimenko's coma. This, plus the detection of phosphorus, is consistent with the hypothesis that the Comets played a crucial role in the emergence of life on Earth.
In 2019, the detection of extraterrestrial sugars in meteorites raised the possibility that extraterrestrial sugars may have contributed to forming functional biopolymers such as RNA.
In 2020, a detailed study of an Allende meteorite named Acfer 086, identified a protein containing iron and lithium, called hemolithin by researchers, of extraterrestrial origin, the first discovery of its kind in a meteorite.
Alien Life
The chemistry of life may have started shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10-17 million years old. According to the panspermia hypothesis, microscopic life, distributed by meteoroids, asteroids, and other small bodies in the Solar System, can exist throughout the universe. However, Earth is the only place in the universe known to humans to harbor life. where life is possible, living organisms could more easily enter the other Solar System bodies from Enceladus. However, the large number of planets in the Milky Way may make it likely that life arose elsewhere of the galaxy and the universe. It is generally accepted that the conditions required for the evolution of intelligent life as we know it are probably extremely rare in the universe, although at the same time it is noted that simple unicellular microorganisms are more likely.
The number of extrasolar planets (exoplanets) is the result of the Kepler mission estimate between 100 and 400 billion exoplanets, with more than 3,500 as candidate or confirmed exoplanets. On November 4, 2013, astronomers reported, based on data from the Kepler space mission, that there could be as many as 40 billion Earth-size planets orbiting in the habitable zones of Sun-like stars and red dwarf stars within the Milky Way. these estimated planets may be orbiting stars similar to the Sun. The closest such planet may be 12 light-years away, according to scientists.
It is estimated that space travel to cosmic distances would take an incredibly long time for an outside observer and with a large amount of energy required. However, some scientists hypothesize that faster-than-light interstellar space travel might be feasible. This has been explored by NASA scientists since at least 1995.
Hypotheses about extraterrestrial sources of diseases
Hoyle and Wickramasinghe have speculated that several disease outbreaks on Earth are of extraterrestrial origin, including the 1918 flu pandemic, certain outbreaks of polio, and mad cow disease (bovine spongiform encephalopathy). For the 1918 flu pandemic, they hypothesized that cometary dust brought the virus to Earth simultaneously in multiple locations, a view almost universally dismissed by experts on this pandemic. Hoyle also speculated that HIV came from outer space.
After Hoyle's death, The Lancet published a letter to the editor from Wickramasinghe and two of his colleagues, in which they hypothesized that the virus that causes severe acute respiratory syndrome (SARS) could be of extraterrestrial origin and not of chickens. The Lancet subsequently published three responses to this letter, showing that the hypothesis was not evidence-based and casting doubt on the quality of the experiments cited by Wickramasinghe in his letter. A 2008 encyclopedia notes that & "Like other claims linking terrestrial diseases to extraterrestrial pathogens, this proposal was rejected by the broader research community."
In April 2016, Jiangwen Qu of China's Department of Infectious Disease Control presented a statistical study suggesting that "extremes of sunspot activity within a year or so can precipitate pandemics of influenza". She discussed possible mechanisms of epidemic initiation and early spread, including speculation about primary causation by externally derived viral variants from space via cometary dust.
Case studies
- In 1996, it was shown that a meteorite from Mars known as ALH84001 contained microscopic structures that resemble small terrestrial nanobacteria. When the discovery was announced, many conjectured immediately that it was fossils and were the first evidence of extraterrestrial life, which reached the headlines of the world. The public interest soon began to decline as most experts began to agree that these structures were not indicative of life, but could be formed abioticly from organic molecules. However, in November 2009, a team of scientists from the Johnson Space Center, including David McKay, reaffirmed that there were "solid proofs that life could have existed in the former Mars," after having re-examined the meteorite and found magnetite crystals.
- On May 11, 2001, two researchers from the University of Naples found viable alien bacteria within a meteorite. The geologist Bruno D'Argenio and the molecular biologist Giuseppe Geraci found the bacteria embedded within the crystalline structure of the minerals, but rose when a sample of the rock was placed in a medium of cultivation.
- A team of Indian and British researchers led by Chandra Wickramasinghe reported in 2001 that air samples on Hyderabad, India, collected from the stratosphere by the Indian Space Research Organization (ISRO) on 21 January 2001, contained live cell groups. Wickramasinghe calls this "unmistakable evidence of the presence of live cell groups in air samples up to 41 km, above which normally no air would be transported from below". Two bacterial species and a fungal were later isolated independently from these filters that were identified as Bacillus simplex, Staphylococcus pasteuri and Engyodontium albumrespectively. Pushkar Ganesh Vaidya of the Indian Astrobiology Research Center reported in 2009 that "the three microorganisms captured during the balloon experiment do not exhibit different adaptations that are expected to be seen in the microorganisms that occupy a comet niche."
- In 2005, ISRO performed an improved experiment. Air samples from the atmosphere were collected from 20 km to more than 40 km on 20 April 2005. The samples were analyzed in two laboratories in India. The laboratories found 12 bacterial species and 6 different fungi in these samples. The mushrooms were Penicillium decumbens, Cladosporium cladosporioides, Alternaria sp. and Tilletiopsis albescens. Of the 12 bacterial samples, three were identified as new species and called Janibacter Hoylei (in honor of Fred Hoyle) Bacillus isronensis (in honour of ISRO) and Bacillus aryabhattai (so called by the ancient Indian mathematician, Aryabhata). These three new species showed they were more resistant to ultraviolet radiation than similar bacteria.
- Some other researchers have recovered bacteria from the stratosphere since the 1970s. The atmospheric sampling performed by NASA in 2010 before and after hurricanes, collected 314 different types of bacteria; the study suggests that large-scale convection during tropical storms and hurricanes can transport this material from the surface to the atmosphere.
- Another proposed mechanism of spores in the stratosphere is to rise by the magnetism of the Earth and the climate to the ionosphere in the low Earth orbit, where the Russian astronauts recovered DNA from a known sterile outer surface of the International Space Station. Russian scientists also speculated on the possibility "that the common terrestrial bacteria are constantly refueling from space."
- In 2013, Dale Warren Griffin, a microbiologist working at the U.S. Geological Service, noted that the viruses are the most numerous entities on Earth. Griffin speculates that viruses evolved in comets and on other planets and moons can be pathogens for humans, so he proposed to also look for viruses on moons and planets of the Solar System.
Hoaxes
In 1965 it was discovered that a separate fragment of the Orgueil meteorite (kept in a sealed glass jar since its discovery) had an embedded seed capsule, while the original glassy layer on the outside remained intact. Despite great initial enthusiasm, the seed was found to be that of a European Juncaceae or Rush plant that had been glued to the fragment and camouflaged with coal dust. The "fusion layer" exterior was in fact glue. Although the author of this hoax is unknown, it is believed that he intended to influence the 19th century debate about spontaneous generation, instead of panspermia, by demonstrating the transformation of inorganic matter into biological matter.
Extremophiles
Hydrothermal vents can support extremophile bacteria on Earth and can also support life in other parts of the cosmos.
Until the 1970s, life was thought to depend on your access to sunlight. It was believed that even life in the depths of the ocean, where sunlight cannot reach, fed by eating organic debris that washed down from surface waters or by animals that did so. However, in 1977, during On an exploratory dive to the Galapagos Hot Spot on the deep-sea exploration submersible Alvin, scientists discovered colonies of assorted creatures clustered around underwater volcanic features known as black smokers.
It was soon determined that the base of this food chain is a form of bacteria that derives its energy from the oxidation of reactive chemicals, such as hydrogen or hydrogen sulfide, that bubble up from within the Earth. This chemosynthesis revolutionized the study of biology by revealing that terrestrial life need not depend on the Sun; it only requires water and an energy gradient to exist.
It is now known that extremophiles, microorganisms with an extraordinary ability to thrive in the harshest environments on Earth, can specialize to thrive in the deep sea, ice, boiling water, acid, the core of nuclear reactor water, salt crystals, toxic waste, and in a variety of other extreme habitats previously thought to be inhospitable to life. Live bacteria found in ice core samples taken from 3,700 meters (12,100 ft) deep in Lake Vostok in Antarctica, have provided data to extrapolate the probability that microorganisms survive frozen in extraterrestrial habitats or during interplanetary transport. In addition, bacteria have been discovered to live within warm rocks deep within the Earth's crust. Metallosphaera sedula it can grow on meteorites in a laboratory.
To test the potential resilience of some of these organisms in outer space, plant seeds and spores of bacteria, fungi, and ferns have been exposed to the harsh space environment. Spores are produced as part of the life cycle normal of many plants, algae, fungi and some protozoa, and some bacteria produce endospores during times of stress. These structures can be highly resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants, while being metabolically inactive. Spores germinate when favorable conditions are restored after exposure to conditions fatal to the parent organism.
Although computer models suggest that a captured meteoroid would normally take a few tens of millions of years before colliding with a planet, there are documented viable terrestrial bacterial spores that are 40 million years old and highly resistant to radiation, and others capable of resuming life after being dormant for 100 million years, suggesting that lithopanspermia life transfers are possible via meteorites larger than 1 m in size.
The discovery of deep-sea ecosystems, along with advances in the fields of astrobiology, observational astronomy, and the discovery of large varieties of extremophiles, opened a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats and the possible transport of resistant microbial life across vast distances.
Research in outer space
The question of whether certain microorganisms can survive in the harsh environment of outer space has intrigued biologists since the dawn of space flight, and opportunities to expose samples to space have provided themselves. The first American tests were carried out in 1966, during the Gemini IX and XII missions, when samples of the T1 bacteriophage and Penicillium roqueforti spores were exposed to outer space for 16.8 h and 6.5 h, respectively. Other life sciences of basic research in low-Earth orbit began in 1966 with the Soviet Bion biosatellite program and the US biosatellite program. Therefore, the plausibility of panspermia can be assessed by examining life forms on Earth to determine their ability to survive in space. The following experiments carried out in low-Earth orbit specifically tested some aspects of panspermia or lithopanspermia:
WAS
The Exobiology Radiation Assembly (ERA) mission was a 1992 experiment aboard the European Retrievable Carrier (EURECA) on the biological effects of space radiation. EURECA was a 4.5 ton unmanned satellite with a payload of 15 experiments. It was an astrobiology mission developed by the European Space Agency (ESA). Spores of different strains of Bacillus subtilis and the pUC19 plasmid of Escherichia coli were exposed to certain space conditions (space vacuum and/or wavebands and intensities of ultraviolet solar radiation defined). After the mission of approximately 11 months, their responses were studied in terms of survival, mutagenesis at the his locus (B. subtilis) or lac (pUC19), induction of DNA strand breaks, efficiency of DNA repair systems and the role of external protective agents. The data was compared to that of a concurrent ground control experiment:
- Survival of spores treated with space vacuum, although protected against solar radiation, increases substantially if exposed in multilayers and/or in the presence of glucose as protector.
- All the spores of the "artificial meteorites", that is, embedded in clays or simulated martian soil, die.
- Vacuum treatment leads to an increase in the frequency of mutation in the spores, but not in the plasma DNA.
- Ultraviolet extraterrestrial solar radiation is mutagenic, induces breakages of strands in DNA and substantially reduces survival.
- Spectroscopy action confirms the results of previous spatial experiments of synergistic action of space vacuum and solar UV radiation, with DNA being the critical target.
- Decreasing the viability of microorganisms could be correlated with increased DNA damage.
- Purple membranes, amino acids and urea were not significantly affected by the dehydrating condition of open space, if protected from solar radiation. Plasmidic DNA, however, suffered a significant amount of breakages in these conditions.
BIOPAN
BIOPAN is a multi-user experimental facility installed on the outer surface of the Russian Foton descent capsule. The experiments developed for BIOPAN are designed to investigate the effect of the space environment on biological material after exposure between 13 and 17 days. The experiments in BIOPAN are exposed to solar and cosmic radiation, space vacuum and weightlessness, or a mixture thereof. Of the 6 missions carried out so far in BIOPAN between 1992 and 2007, dozens of experiments have been carried out, and some have analyzed the probability of panspermia. Some bacteria, lichens (Xanthoria elegans, Rhizocarpon geographicum and their mycobiont cultures, the Antarctic black microfungi Cryomyces minteri and Cryomyces antarcticus), spores, and even one animal (tardigrades) survived the harsh environment of outer space and cosmic radiation.
EXOSTACK
The German EXOSTACK experiment was deployed on April 7, 1984 aboard the Long Duration Exposure Facility satellite. 30% of Bacillus subtilis spores survived exposure of almost 6 years when embedded in salt crystals, while 80% survived in the presence of glucose, which stabilizes the structure of macromolecules cells, especially during vacuum-induced dehydration.
If protected from solar UV rays, the spores of B. subtilis could survive in space for up to 6 years, especially if embedded in clay or meteorite dust (artificial meteorites). The data support the probability of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis.
EXPOSE
EXPOSE is a multi-user facility set up outside the International Space Station dedicated to astrobiology experiments. Three EXPOSE experiments have been carried out between 2008 and 2015: EXPOSE-E, EXPOSE-R and EXPOSE-R2. The results of the orbital missions, especially the SEEDS and LiFE experiments, concluded that after an 18-month exposure, some seeds and lichens (Stichococcus sp.. And Acarospora sp.) a genus of lichenized fungi, may be able to survive interplanetary travel if protected inside comets or rocks from cosmic radiation and ultraviolet radiation. The LIFE, SPORES and SEEDS parts of the experiments provided information on the probability of lithopanspermia. These studies will provide experimental data to the hypothesis of the lithopanspermia, and will provide basic data on planetary protection issues.
Tanpopo
The Tanpopo mission is an orbital astrobiology experiment in Japan currently investigating the possible interplanetary transfer of life, organic compounds, and possible Earth particles in low-Earth orbit. Tanpopo's experiment took place in the Exposed Facility located outside the Kibo module of the International Space Station. The mission collected cosmic dust and other particles over three years using an ultra-low-density silica gel called aerogel. The purpose is to test the panspermia hypothesis and the possibility of natural interplanetary transport of life and its precursors. Some of these aerogels were replaced every one to two years until 2018. Sample collection began in May 2015, and the first samples were returned to Earth in mid-2016.
In August 2020, scientists reported that bacteria on Earth, particularly the Deinococcus radiodurans bacterium, which is highly resistant to environmental hazards, survived for three years in outer space, according to studies carried out on the International Space Station.
Criticism
Panspermia is often criticized because it does not answer the question of the origin of life, but simply places it on another celestial body. It was also criticized because it was thought that it could not be tested experimentally.
Wallis and Wickramasinghe argued in 2004 that the transport of individual bacteria or groups of bacteria is overwhelmingly more important than lithopanspermia in terms of the number of microbes transferred, even taking into account the rate of death of unprotected bacteria in transit. it was discovered that the spores isolated from B. subtilis died by several orders of magnitude if exposed to the entire space environment for a few seconds. Although these results may seem to deny the original panspermia hypothesis, the type of microorganism making the long journey is inherently unknown and so are its unknown characteristics. Then it might be impossible to rule out the hypothesis based on the resistance of a few soil-evolved microorganisms. Furthermore, if protected against UV sunlight, Bacillus subtilis spores were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite dust (artificial meteorites). The data support the probability of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis.
Testing the hypothesis
There are studies that suggest the possible existence of bacteria capable of surviving long periods of time even in outer space. Bacteria have also been found in the atmosphere at altitudes of more than 40 km where it is possible, though unlikely, that they may have come from the lower layers.
Some Streptococcus mitis bacteria that were accidentally transported to the Moon in 1967 in the Surveyor 3 spacecraft could be revived without difficulty upon their return to Earth three years later.
Analysis of the ALH84001 meteorite, thought to have originated on the planet Mars, shows structures that could have been caused by microscopic life forms. This is as close to a hint of extraterrestrial life as it has been possible to get, and it remains highly controversial. On the other hand, uracil and xanthine, two precursors of the molecules that make up RNA and DNA, have been found in the Murchison meteorite.
Alien sugars in meteorites indicate the possibility that extraterrestrial sugars may have contributed to the formation of functional biopolymers such as RNA. In 2020, detailed study of a meteorite identified an iron- and lithium-containing protein of extraterrestrial origin.
On the other hand, one of the most significant proofs has finally been refuted. In 2006, the intense orange microorganisms that caused the staining of the red rainwater of Kerala in 2001, in southern India, were studied, attributing them to a possible extraterrestrial origin. However, in 2015, they could be identified by ribosomal DNA as the spores of a species of the alga Trentepohlia, T. annulata, of European origin and previously undescribed from India. The discovery of many varieties of extremophiles opened a new avenue in astrobiology by massively expanding the number of possible extraterrestrial habitats and possible transport of microbial life. resistant over great distances.
Criticism and evidence against the hypothesis
The biggest drawback of this hypothesis is that it does not solve the initial problem of how life arose (biogenesis), but merely shifts the responsibility for its origin to another place in space.
Another objection is that bacteria would not survive the extremely high temperatures and the forces involved in an impact against the Earth, although no conclusions have yet been reached on this point (neither for nor against), since they are known some species of extremophile bacteria. However, in experiments that recreate the conditions of comets bombarding the Earth, organic molecules, such as amino acids, are not only not destroyed, but begin to form peptides. Also, the time it would take to travel is not counted. the distance from the supposed living object to Earth.
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