Editing Panspermia (section)

===Radiopanspermia===
In 1903, [[Svante Arrhenius]] proposed radiopanspermia, the theory that singular microscopic forms of life can be propagated in space, driven by the [[radiation pressure]] from stars.<ref>{{Citation |title=V. Die Verbreitung des organischen Lebens auf der Erde |date=1885-12-31 |url=http://dx.doi.org/10.1515/9783112690987-006 |work=Anthropologische Studien |pages=101–133 |access-date=2023-11-28 |publisher=De Gruyter |doi=10.1515/9783112690987-006 |isbn=978-3-11-269098-7}}</ref> This is the mechanism by which light can exert a force on matter. Arrhenius argued that particles at a critical size below 1.5 μm would be propelled at high speed by radiation pressure of a star.<ref name=":103"/> However, because its effectiveness decreases with increasing size of the particle, this mechanism holds for very tiny particles only, such as single [[Endospore|bacterial spores]].

==== Counterarguments ====
The main criticism of radiopanspermia came from [[Iosif Shklovsky]] and [[Carl Sagan]], who cited evidence for the [[Health threat from cosmic rays|lethal action of space radiation]] ([[UV]] and [[X-ray]]s) in the cosmos.<ref>{{Citation |title=The Intelligent Universe |date=2020-09-24 |url=http://dx.doi.org/10.1017/9781108873154.026 |work=The Biological Universe |pages=318–334 |access-date=2023-11-28 |publisher=Cambridge University Press |doi=10.1017/9781108873154.026 |isbn=978-1-108-87315-4|s2cid=116975371 }}</ref> If enough of these microorganisms are ejected into space, some may rain down on a planet in a new star system after 10<sup>6</sup> years wandering interstellar space.{{cn|date=September 2024}} There would be enormous death rates of the organisms due to radiation and the generally hostile conditions of space, but nonetheless this theory is considered potentially viable by some.{{cn|date=September 2024}}

Data gathered by the orbital experiments [[Exobiology Radiation Assembly|ERA]], [[BIOPAN]], [[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).<ref>{{Cite journal |last1=Horneck |first1=Gerda |last2=Rettberg |first2=Petra |last3=Reitz |first3=Günther |last4=Wehner |first4=Jörg |last5=Eschweiler |first5=Ute |last6=Strauch |first6=Karsten |last7=Panitz |first7=Corinna |last8=Starke |first8=Verena |last9=Baumstark-Khan |first9=Christa |date=2001 |title=Protection of bacterial spores in space, a contribution to the discussion on Panspermia |url=http://link.springer.com/10.1023/A:1012746130771 |journal=Origins of Life and Evolution of the Biosphere |volume=31 |issue=6 |pages=527–547 |doi=10.1023/A:1012746130771|pmid=11770260 |bibcode=2001OLEB...31..527H |s2cid=24304433 }}</ref> Spores would therefore need to be heavily protected against UV radiation: exposure of unprotected DNA [[UV exposure|to solar UV]] and [[Cosmic ray|cosmic]] [[ionizing radiation]] would break it up into its constituent bases.<ref>{{Cite journal |last1=Patrick |first1=Michael H. |last2=Gray |first2=Donald M. |date=December 1976 |title=INDEPENDENCE OF PHOTOPRODUCT FORMATION ON DNA CONFORMATION* |url=http://dx.doi.org/10.1111/j.1751-1097.1976.tb06867.x |journal=Photochemistry and Photobiology |volume=24 |issue=6 |pages=507–513 |doi=10.1111/j.1751-1097.1976.tb06867.x |pmid=1019243 |s2cid=12711656 |issn=0031-8655}}</ref> Rocks at least 1 meter in diameter are required to effectively shield resistant microorganisms, such as bacterial spores against galactic [[cosmic radiation]].<ref>{{Cite journal |last=Mileikowsky |first=C |date=June 2000 |title=Natural Transfer of Viable Microbes in Space 1. From Mars to Earth and Earth to Mars |url=http://dx.doi.org/10.1006/icar.1999.6317 |journal=Icarus |volume=145 |issue=2 |pages=391–427 |doi=10.1006/icar.1999.6317 |pmid=11543506 |bibcode=2000Icar..145..391M |issn=0019-1035}}</ref> Additionally, exposing DNA to the [[Ultra-high vacuum|ultrahigh vacuum]] of space alone is sufficient to cause [[DNA damage]], so the transport of unprotected DNA or [[RNA]] during [[Interplanetary spaceflight|interplanetary flights]] powered solely by [[light pressure]] is extremely unlikely.<ref>{{Cite journal |last1=Nicholson |first1=Wayne L. |last2=Schuerger |first2=Andrew C. |last3=Setlow |first3=Peter |date=2005-04-01 |title=The solar UV environment and bacterial spore UV resistance: considerations for Earth-to-Mars transport by natural processes and human spaceflight |url=https://linkinghub.elsevier.com/retrieve/pii/S0027510704004981 |journal=Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis |language=en |volume=571 |issue=1–2 |pages=249–264 |doi=10.1016/j.mrfmmm.2004.10.012|pmid=15748651 |bibcode=2005MRFMM.571..249N }}</ref>

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. There is little evidence in full support of the radiopanspermia hypothesis.