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 testable, test it. Scientists generally base scientific hypotheses on prev ...
, first proposed in the 5th century BCE by the Greek philosopher
Anaxagoras
Anaxagoras (; grc-gre, Ἀναξαγόρας, ''Anaxagóras'', "lord of the assembly"; 500 – 428 BC) was a Pre-Socratic Greek philosopher. Born in Clazomenae at a time when Asia Minor was under the control of the Persian Empire, ...
, 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. A ...
, distributed by
space dust,
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 mic ...
s,
asteroids,
comets,
and
planetoids, as well as by
spacecraft
A spacecraft is a vehicle or machine designed to spaceflight, fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth ...
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
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 ...
.
[Forward planetary contamination like '']Tersicoccus phoenicis
''Tersicoccus phoenicis'' is a member of the bacterial family Micrococcaceae. It has only been found in two Cleanroom, spacecraft assembly clean room facilities and is resistant to the methods normally used to clean such facilities. The species ...
'', that has shown resistance to methods usually used in spacecraft assembly clean rooms: Panspermia is a
fringe theory 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 lifeforms 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 tempe ...
s) can become trapped in
debris ejected into space after collisions between planets and
small Solar System bodies 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 (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
Anaxagoras (; grc-gre, Ἀναξαγόρας, ''Anaxagóras'', "lord of the assembly"; 500 – 428 BC) was a Pre-Socratic Greek philosopher. Born in Clazomenae at a time when Asia Minor was under the control of the Persian Empire, ...
.
[ 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
Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be ...
(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 ph ...
(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 testable, test it. Scientists generally base scientific hypotheses on prev ...
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 N ...
(1903).
Fred Hoyle (1915–2001) and
Chandra Wickramasinghe
Nalin Chandra Wickramasinghe (born 20 January 1939) is a Sri Lankan-born British mathematician, astronomer and astrobiologist of Sinhalese people, Sinhalese ethnicity. His research interests include the interstellar medium, infrared astronomy, ...
(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.
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
Panspermia can be said to be either interstellar (between
star system
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speakin ...
s) 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 procedures to reduce the risk of planetary contamination, but microorganisms such as ''Tersicoccus phoenicis
''Tersicoccus phoenicis'' is a member of the bacterial family Micrococcaceae. It has only been found in two Cleanroom, spacecraft assembly clean room facilities and is resistant to the methods normally used to clean such facilities. The species ...
'' may be resistant to spacecraft assembly cleaning.
Origination and distribution of organic molecules: Pseudo-panspermia
Pseudo-panspermia is the well-supported hypothesis that many of the small organic molecules 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 ...
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 surf ...
, 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 hypothe ...
. 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 N ...
proposed radiopanspermia, that microscopic forms of life can be propagated in space, driven by the radiation pressure 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 and Carl Sagan
Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ...
, who pointed out the evidence for the lethal action of space radiation ( UV and X-ray
X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...
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, 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 vacuum ...
, EXOSTACK and EXPOSE showed that isolated spores, including those of '' B. subtilis'', 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 (cometary), coma, and sometimes also a Comet ta ...
s or asteroid
An asteroid is a minor planet of the Solar System#Inner solar system, 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 o ...
s, remains speculative. A variant would be for organisms to travel between star systems on nomadic exoplanets or exomoons.
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'' 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 und ...
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 the ...
of microorganisms on lifeless planets. The Nobel prize winner Francis Crick
Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the helical stru ...
, along with Leslie Orgel 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 existenc ...
" Crick noted later that life may have originated on Earth. The astronomer Thomas Gold 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 pr ...
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 ...
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
The phi X 174 (or ΦX174) bacteriophage is a single-stranded DNA ( ssDNA) virus that infects ''Escherichia coli'', and the first DNA-based genome to be sequenced. This work was completed by Fred Sanger and his team in 1977. In 1962, Walter Fier ...
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 or viral replication, m ...
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
Orgueil (; oc, Orgulh) is a commune in the Tarn-et-Garonne department in the Occitanie region in southern France.
History
Orgueil has existed for more than 1000 years. It was first mentioned in the 9th century, when Orgueil was part of Saint- ...
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. 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 i ...
'', 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 i ...
'', 29 November 2020
{{Extraterrestrial life
Panspermia
Astrobiology
Origin of life
Biological hypotheses
Prebiotic chemistry
Fringe science