![Panspermie](https://upload.wikimedia.org/wikipedia/commons/4/48/Panspermie.svg)
Panspermia () is the
hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
, first proposed in the 5th century BCE by the Greek philosopher
Anaxagoras, that
life
Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...
exists throughout the
Universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...
, distributed by
space dust
Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...
,
meteoroid
A meteoroid () is a small rocky or metallic body in outer space.
Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mi ...
s,
asteroids
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
,
comets
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
,
and
planetoids
According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''mino ...
, as well as by
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
carrying unintended
contamination
Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc.
Types of contamination
...
by
microorganisms.
[Forward planetary contamination like '' Tersicoccus phoenicis'', that has shown resistance to methods usually used in spacecraft assembly clean rooms: ] Panspermia is a
fringe theory
A fringe theory is an idea or a viewpoint which differs from the accepted scholarship of the time within its field. Fringe theories include the models and proposals of fringe science, as well as similar ideas in other areas of scholarship, such a ...
with little support amongst mainstream scientists.
Critics argue that it does not answer the question of the
origin of life
In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothes ...
but merely places it on another celestial body. It is also criticized because it cannot be tested experimentally.
Panspermia proposes (for example) that
microscopic life
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
forms which can survive the effects of space (such as
extremophile
An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme temper ...
s) can become trapped in
debris ejected into space after collisions between planets and
small Solar System bodies
A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other objects, ...
that harbor life.
Panspermia studies concentrate not on how life began, but on methods that may distribute it in the Universe.
[A variation of the panspermia hypothesis is necropanspermia which astronomer Paul Wesson describes as follows: "The vast majority of organisms reach a new home in the Milky Way in a technically dead state … Resurrection may, however, be possible." ][Hoyle, F. and Wickramasinghe, N.C. (1981). ''Evolution from Space''. Simon & Schuster, New York, and J.M. Dent and Son, London (1981), ch. 3 pp. 35–49.][Wickramasinghe, J., Wickramasinghe, C. and Napier, W. (2010)]
''Comets and the Origin of Life''
World Scientific, Singapore. ch. 6 pp. 137–154.
Pseudo-panspermia
Pseudo-panspermia (sometimes called soft panspermia, molecular panspermia or quasi-panspermia) is a well-supported hypothesis for a stage in the origin of life. The theory first asserts that many of the small organic molecules used for life origina ...
(sometimes called ''soft panspermia'' or ''molecular panspermia'') is the well-attested hypothesis that many of the pre-biotic organic building-blocks of life originated in space, became incorporated in the solar nebula from which planets condensed, and were further—and continuously—distributed to planetary surfaces where
life then emerged.
History
The first mention of panspermia was in the writings of the fifth-century BC
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
philosopher
Anaxagoras.
[ The Panspermia hypothesis states that life exists elsewhere in the universe, and could be distributed far and wide. This idea was first introduced by the ancient Greek philosopher Anaxagoras (5th Century BCE), who believed that the universe is made of an infinite number of seeds ("spermata" in Greek). Upon reaching the Earth, these seeds gave rise to life. Anaxagorus introduced the term "Panspermia", which in Greek means literally "seeds everywhere".] Panspermia began to assume a more scientific form through the proposals of
Jöns Jacob Berzelius (1834), Hermann E. Richter (1865),
Kelvin
The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phy ...
(1871),
Hermann von Helmholtz
Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Associatio ...
(1879) and finally reaching the level of a detailed scientific
hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
through the efforts of the Swedish chemist
Svante Arrhenius
Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. He received the Nob ...
(1903).
Fred Hoyle
Sir Fred Hoyle FRS (24 June 1915 – 20 August 2001) was an English astronomer who formulated the theory of stellar nucleosynthesis and was one of the authors of the influential B2FH paper. He also held controversial stances on other sci ...
(1915–2001) and
Chandra Wickramasinghe (born 1939) were influential proponents of panspermia.
In 1974 they proposed the hypothesis that some
dust in interstellar space was largely
organic (containing carbon), which Wickramasinghe later proved to be correct. 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
macroevolution
Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation). In other words, macroevolution is the evolution of taxa abov ...
.
Overview
Core requirements
Panspermia requires:
# that organic molecules originated in space (perhaps to be distributed to Earth)
# that life originated from these molecules, extraterrestrially
# that this extraterrestrial life was transported to Earth.
The creation and distribution of organic molecules from space is now uncontroversial; it is known as pseudo-panspermia.
The existence of
extraterrestrial life is unconfirmed but scientifically possible. The transport of such life to Earth is considered pseudo-science.
Interstellar or interplanetary
![ISS space station modules in the SSPF](https://upload.wikimedia.org/wikipedia/commons/9/92/ISS_space_station_modules_in_the_SSPF.jpg)
Panspermia can be said to be either interstellar (between
star systems) or interplanetary (between
planets in the same star system).
The major proposed mechanisms for panspermia are radiopanspermia, the propulsion of microbes through space by radiation pressure;
lithopanspermia, the transfer of organisms inside rocks, shielded from the space environment;
[ and directed panspermia, managed deliberately to seed planetary systems with life.]
Space probe
A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or ...
s may be a viable transport mechanism for interplanetary cross-pollination within the Solar System. Space agencies have implemented planetary protection
Planetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of sample-return missions. Planetary protection reflec ...
procedures to reduce the risk of planetary contamination, but microorganisms such as '' Tersicoccus phoenicis'' may be resistant to spacecraft assembly cleaning.
Origination and distribution of organic molecules: Pseudo-panspermia
Pseudo-panspermia
Pseudo-panspermia (sometimes called soft panspermia, molecular panspermia or quasi-panspermia) is a well-supported hypothesis for a stage in the origin of life. The theory first asserts that many of the small organic molecules used for life origina ...
is the well-supported hypothesis that many of the small organic molecule
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s used for life
Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...
originated in space, and were distributed to planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
ary surfaces. Life then emerged on Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
, and perhaps on other planets, by the processes of abiogenesis
In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothes ...
. Evidence for pseudo-panspermia includes the discovery of organic compounds such as sugars, amino acids, and nucleobases in meteorites and other extraterrestrial bodies, and the formation of similar compounds in the laboratory under outer space conditions. A prebiotic polyester system has been explored as an example.
Radiopanspermia
Hypothesis
In 1903, Svante Arrhenius
Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. He received the Nob ...
proposed radiopanspermia, that microscopic forms of life can be propagated in space, driven by the radiation pressure
Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is a ...
from stars. Arrhenius argued that particles at a critical size below 1.5 μm would be propelled 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.
Counter-arguments
The main criticism of radiopanspermia came from Iosif Shklovsky
Iosif Samuilovich Shklovsky (russian: Ио́сиф Самуи́лович Шкло́вский; sometimes transliterated ''Josif, Josif, Shklovskii, Shklovskij'') (1 July 1916 – 3 March 1985) was a Soviet astronomer and astrophysicist. He ...
and Carl Sagan, who pointed out the evidence for the lethal action of space radiation ( UV and X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s) in the cosmos. 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.
Data gathered by the orbital experiments ERA
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comp ...
, BIOPAN
BIOPAN is a multi-user research program by the European Space Agency (ESA) designed to investigate the effect of the space environment on biological material. The experiments in BIOPAN are exposed to solar and cosmic radiation, the space vacuu ...
, EXOSTACK
NASA's Long Duration Exposure Facility, or LDEF (pronounced "eldef"), was a school bus-sized cylindrical facility designed to provide long-term experimental data on the outer space environment and its effects on space systems, materials, operatio ...
and EXPOSE
Expose, exposé, or exposed may refer to:
News sources
* Exposé (journalism), a form of investigative journalism
* '' The Exposé'', a British conspiracist website
Film and TV Film
* ''Exposé'' (film), a 1976 thriller film
* ''Exposed'' (1932 ...
showed that isolated spores, including those of ''B. subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...
'', were rapidly killed if exposed to the full space environment for merely a few seconds, but if shielded against solar UV, the spores were capable of surviving in space for up to six years while embedded in clay or meteorite powder (artificial meteorites).
Spores would therefore need to be heavily protected against UV radiation: exposure of unprotected DNA to solar UV and cosmic ionizing radiation would break it up into its constituent bases. 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 powered solely by light pressure is extremely unlikely.
The feasibility of other means of transport for the more massive shielded spores into the outer Solar System—for example, through gravitational capture by comets—is unknown. Rocks at least 1 meter in diameter are required to effectively shield resistant microorganisms, such as bacterial spores against galactic cosmic radiation. These results clearly negate the radiopanspermia hypothesis.
Lithopanspermia
Hypothesis
Lithopanspermia, the transfer of organisms in rocks from one planet to another either through interplanetary or interstellar space, such as in comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s or asteroids, remains speculative.
A variant would be for organisms to travel between star systems on nomadic exoplanets or exomoons.
The travel of rocks between stars in our galaxy is estimated to take millions of years, which is less than the billions of years that life on Earth has evolved.
Although there is no evidence that lithopanspermia has occurred in the Solar System, the various stages have become amenable to experimental testing.
* Planetary ejection – For lithopanspermia to occur, microorganisms must survive ejection from a planetary surface, which involves extreme forces of acceleration and shock with associated temperature excursions. Hypothetical values of shock pressures experienced by ejected rocks are obtained with Martian meteorites, which suggest the shock pressures of approximately 5 to 55 GPa, acceleration of 3 Mm/s2 and jerk of 6 Gm/s3 and post-shock temperature increases of about 1 K to 1000 K. Some organisms appear able to survive these conditions.
* Survival in transit – The survival of microorganisms has been studied extensively using both simulated facilities and in low Earth orbit. A large number of microorganisms have been selected for exposure experiments, both human-borne microbes (significant for future crewed missions) and extremophiles
An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tempe ...
(significant for determining the physiological requirements of survival in space).
* Atmospheric entry – to test whether microbes on or within rocks could survive hypervelocity entry through Earth's atmosphere. Tests could use sounding rockets and orbital vehicles. ''B. subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...
'' spores inoculated onto granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...
domes were twice subjected to hypervelocity atmospheric transit by launch to a ∼120 km altitude on an Orion two-stage rocket. The spores survived on the sides of the rock, but not on the forward-facing surface that reached 145 °C. As photosynthetic organisms must be close to the surface of a rock to obtain sufficient light energy, atmospheric transit might act as a filter against them by ablating the surface layers of the rock. Although cyanobacteria can survive the desiccating, freezing conditions of space, the STONE experiment showed that they cannot survive atmospheric entry. Small non-photosynthetic organisms deep within rocks might survive the exit and entry process, including impact survival.
Directed panspermia
Hypothesis
Directed panspermia would be the deliberate transport of microorganisms in space, sent to Earth to start life here, or sent from Earth to seed new planetary systems with life by introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...
of microorganisms on lifeless planets. The Nobel prize winner Francis Crick, along with Leslie Orgel
Leslie Eleazer Orgel FRS (12 January 1927 – 27 October 2007) was a British chemist. He is known for his theories on the origin of life.
Biography
Leslie Orgel was born in London, England, on . He received his Bachelor of Arts degree in chemi ...
proposed that life may have been purposely spread by an advanced extraterrestrial civilization, but considering an early "RNA world
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existen ...
" Crick noted later that life may have originated on Earth. The astronomer Thomas Gold
Thomas Gold (May 22, 1920 – June 22, 2004) was an Austrian-born American astrophysicist, a professor of astronomy at Cornell University, a member of the U.S. National Academy of Sciences, and a Fellow of the Royal Society (London). Gold was ...
suggested in 1960 the hypothesis of "Cosmic Garbage", that life on Earth might have originated accidentally from a pile of waste
Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste prod ...
products dumped on Earth long ago by extraterrestrial beings.
Counter-arguments
Directed panspermia could, in theory, be demonstrated by finding a distinctive 'signature' message had been deliberately implanted into either the genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
or the genetic code
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
of the first microorganisms by our hypothetical progenitor, some 4 billion years ago. It has been suggested that the bacteriophage φX174 might represent such a message. However, there is no known mechanism that could prevent mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA replication, DNA or viral repl ...
and natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
from removing such a message over long periods of time.
Hoaxes
A separate fragment of the Orgueil meteorite (kept in a sealed glass jar since its discovery) was found in 1965 to have a seed capsule embedded in it, while the original glassy layer on the outside remained undisturbed. Despite great initial excitement, the seed was found to be that of a European Juncaceae
Juncaceae is a family of flowering plants, commonly known as the rush family. It consists of 8 genera and about 464 known species of slow-growing, rhizomatous, herbaceous monocotyledonous plants that may superficially resemble grasses and s ...
or Rush plant that had been glued into the fragment and camouflaged using coal dust Coal dust is a fine powdered form of which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal. It is a form ...
. The outer "fusion layer" was in fact glue. While the perpetrator of this hoax is unknown, it is thought that they sought to influence the 19th-century debate on spontaneous generation
Spontaneous generation is a superseded scientific theory that held that living creatures could arise from nonliving matter and that such processes were commonplace and regular. It was hypothesized that certain forms, such as fleas, could arise f ...
—rather than panspermia—by demonstrating the transformation of inorganic to biological matter.
See also
*
*
*
*
*
References
Further reading
*
*
External links
* Cox, Brian
"Are we thinking about alien life all wrong?"
BBC Ideas, video made by Pomona Pictures, 29 November 2021.
* Loeb, Abraham
"Did Life from Earth Escape the Solar System Eons Ago?"
''Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...
'', 4 November 2019
* Loeb, Abraham
"Noah's Spaceship"
''Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...
'', 29 November 2020
{{Extraterrestrial life
Panspermia
Astrobiology
Origin of life
Biological hypotheses
Prebiotic chemistry
Fringe science