Editing Outer space (section)

== Regions ==
{{Also|Location of Earth}}
===Regions near the Earth===
The outermost layer of the Earth's atmosphere is termed the [[exosphere]]. It extends outward from the [[thermopause]], which lies at an altitude that varies from {{convert|250|to|500|km|mi}}, depending on the incidence of solar radiation. Beyond this altitude, collisions between molecules are negligible and the atmosphere joins with interplanetary space.<ref name=Catling_Kasting_2017/> The region in proximity to the Earth is home to a multitude of Earth–orbiting satellites and has been subject to extensive studies. For identification purposes, this volume is divided into overlapping regions of space.<ref name="uscode.house.gov 2022"/>{{sfn|Schrijver|Siscoe|2010|p=363, 379}}<ref name=sdc20150426/><ref name=sr2165/>

'''{{Visible anchor|Near-Earth space}}''' is the region of space extending from low Earth orbits out to [[geostationary orbit]]s.<ref name="uscode.house.gov 2022"/> This region includes the major orbits for [[artificial satellite]]s and is the site of most of humanity's space activity. The region has seen high levels of space debris, sometimes dubbed [[space pollution]], threatening nearby space activity.<ref name="uscode.house.gov 2022"/> Some of this debris re-enters Earth's atmosphere periodically.<ref name=portree_loftus1999/> Although it meets the definition of outer space, the atmospheric density inside low-Earth orbital space, the first few hundred kilometers above the Kármán line, is still sufficient to produce significant [[Drag (physics)|drag]] on satellites.<ref name=slsa/>

[[File:Debris-GEO1280.jpg|thumb|A computer-generated map of objects orbiting Earth, as of 2005. About 95% are debris, not working artificial satellites<ref name=ARES/>]]

{{anchor|Geospace}}'''Geospace''' is a region of space that includes Earth's [[upper atmosphere]] and [[magnetosphere]].{{sfn|Schrijver|Siscoe|2010|p=363, 379}} The Van Allen radiation belts lie within the geospace. The outer boundary of geospace is the [[magnetopause]], which forms an interface between the Earth's magnetosphere and the solar wind. The inner boundary is the [[ionosphere]].<ref name=geospace/>{{sfn|Schrijver|Siscoe|2010|p=379}}

The variable space-weather conditions of geospace are affected by the behavior of the Sun and the solar wind; the subject of geospace is interlinked with [[heliophysics]]—the study of the Sun and its impact on the planets of the Solar System.{{sfn|Fichtner|Liu|2011|pp=341–345}} The day-side magnetopause is compressed by solar-wind pressure—the subsolar distance from the center of the Earth is typically 10 Earth radii. On the night side, the solar wind stretches the magnetosphere to form a [[magnetotail]] that sometimes extends out to more than 100–200 Earth radii.{{sfn|Koskinen|2010|pp=32, 42}}<ref name=HonesJr1986/> For roughly four days of each month, the lunar surface is shielded from the solar wind as the Moon passes through the magnetotail.{{sfn|Mendillo|2000|p=275}}

Geospace is populated by electrically charged particles at very low densities, the motions of which are controlled by the [[Earth's magnetic field]]. These plasmas form a medium from which storm-like disturbances powered by the solar wind can drive electrical currents into the Earth's upper atmosphere. [[Geomagnetic storm]]s can disturb two regions of geospace, the radiation belts and the ionosphere. These storms increase fluxes of energetic electrons that can permanently damage satellite electronics, interfering with shortwave radio communication and [[Global Positioning System|GPS]] location and timing.{{sfn|Goodman|2006|p=244}} Magnetic storms can be a hazard to astronauts, even in low Earth orbit. They create [[aurora (astronomy)|aurorae]] seen at high latitudes in an oval surrounding the [[geomagnetic pole]]s.<ref name=oecd/>

[[File:Artemis 1 at maximum distance from Earth.jpg|thumb|Earth and the Moon as seen from cislunar space on the 2022 [[Artemis 1]] mission]]
XGEO space is a concept used by the USA to refer to the space of high Earth orbits, with the 'X' being some multiple of [[geosynchronous orbit]] (GEO) at approximately {{convert|35786|km|mi|0|abbr=on}}.<ref name=sdc20150426/> Hence, the [[Lagrange point#Earth–Moon|L2 Earth-Moon Lagrange point]] at {{convert|448900|km|mi|0|abbr=on}} is approximately 10.67 XGEO.<ref name=Cunio_et_al_2021/> Translunar space is the region of lunar [[transfer orbit]]s, between the Moon and Earth.<ref name="NASA 2013"/> {{anchor|Cislunar space}}{{anchor|cislunar space}} '''Cislunar space''' is a region outside of Earth that includes [[lunar orbit]]s, the [[orbit of the Moon|Moon's orbital space around Earth]] and the Earth-Moon [[Lagrange point]]s.<ref name=sr2165/>

The region where a body's [[gravitational potential]] remains dominant against gravitational potentials from other bodies, is the body's [[Sphere of influence (astrodynamics)|sphere of influence]] or gravity well, mostly described with the [[Hill sphere]] model.<ref name=yoder1995/> In the case of Earth this includes all space from the Earth to a distance of roughly 1% of the mean distance from Earth to the Sun,{{sfn|Barbieri|2006|p=253}} or {{convert|1.5|e6km|e6mi|abbr=unit}}. Beyond Earth's Hill sphere extends along [[Earth's orbit]]al path its orbital and [[co-orbital]] space. This space is co-populated by groups of co-orbital [[Near-Earth Object]]s (NEOs), such as [[Horseshoe orbit|horseshoe librator]]s and [[Earth trojan]]s, with some NEOs at times becoming [[temporary satellite]]s and [[Quasi-satellite|quasi-moon]]s to Earth.<ref name=Granvik_et_al_2012/>

{{anchor|Deep space}}
'''Deep space''' is defined by the United States government as all of outer space which lies further from Earth than a typical low-Earth-orbit, thus assigning the Moon to deep-space.<ref name=USC_10101/> Other definitions vary the starting point of deep-space from, "That which lies beyond the orbit of the moon," to "That which lies beyond the farthest reaches of the Solar System itself."{{sfn|Dickson|2010|p=57}}{{sfn|Williamson|2006|p=97}}<ref name=Collins/> The [[ITU-R|International Telecommunication Union responsible for radio communication]], including with satellites, defines deep-space as, "distances from the Earth equal to, or greater than, {{convert|2|e6km|e6mi|abbr=unit}},"<ref name=ITU/> which is about five times the [[Lunar distance (astronomy)|Moon's orbital distance]], but which distance is also far less than the distance between Earth and any adjacent planet.<ref name=Williams_2021/>
[[File:Orbitalaltitudes.svg|center|700px|thumb|Near-Earth space showing the low-Earth (blue), medium Earth (green), and high Earth (red) orbits. The last extends beyond the radius of geosynchronous orbits]]

=== Interplanetary space ===
{{main|Interplanetary medium}}
[[File:Comet Hale-Bopp 1995O1.jpg|right|thumb|The sparse plasma (blue) and dust (white) in the tail of [[comet Hale–Bopp]] are being shaped by pressure from [[Sunlight|solar radiation]] and the solar wind, respectively.|alt=At lower left, a white coma stands out against a black background. Nebulous material streams away to the top and left, slowly fading with distance.]]

Interplanetary space within the [[Solar System]] is dominated by the gravitation of the Sun, outside the gravitational spheres of influence of the planets.<ref name="j999"/> Interplanetary space extends well beyond the orbit of the outermost planet [[Neptune]], all the way out to where the influence of the galactic environment starts to dominate over the Sun and its solar wind producing the [[Heliopause (astronomy)|heliopause]] at 110 to 160 AU.<ref name=universetoday_interplanetaryspace /> The heliopause deflects away low-energy galactic cosmic rays, and its distance and strength varies depending on the activity level of the solar wind.<ref name=Kohler2017/><ref name=phillips2009/> The solar wind is a continuous stream of charged particles emanating from the Sun which creates a very tenuous atmosphere (the [[heliosphere]]) for billions of kilometers into space. This wind has a particle density of 5–10 [[proton]]s/cm<sup>3</sup> and is moving at a velocity of {{Convert|350|-|400|km/s|mph|abbr=on}}.{{sfn|Papagiannis|1972|pp=12–149}}

The region of interplanetary space is a nearly total vacuum, with a mean free path of about one [[astronomical unit]] at the orbital distance of the Earth. This space is not completely empty, but is sparsely filled with cosmic rays, which include [[ion]]ized [[atomic nucleus|atomic nuclei]] and various subatomic particles. There is gas, plasma and dust,<ref name="EA-20190312"/> small [[meteor]]s, and several dozen types of [[organic chemistry|organic]] molecules discovered to date by [[rotational spectroscopy|microwave spectroscopy]].<ref name=asp2003/> Collectively, this matter is termed the [[interplanetary medium]].<ref name=universetoday_interplanetaryspace /> A cloud of interplanetary dust is visible at night as a faint band called the [[zodiacal light]].<ref name="leinert_grun_1990"/>

Interplanetary space contains the magnetic field generated by the Sun.{{sfn|Papagiannis|1972|pp=12–149}} There are magnetospheres generated by planets such as Jupiter, Saturn, [[Mercury (planet)|Mercury]] and the Earth that have their own magnetic fields. These are shaped by the influence of the solar wind into the approximation of a teardrop shape, with the long tail extending outward behind the planet. These magnetic fields can trap particles from the solar wind and other sources, creating belts of charged particles such as the Van Allen radiation belts. Planets without magnetic fields, such as Mars, have their atmospheres gradually eroded by the solar wind.<ref name=ssr69_3_215/>

=== Interstellar space ===
{{Redirect|Interstellar space|the album|Interstellar Space}}
{{Main|Interstellar medium}}
[[File:52706main hstorion lg.jpg|right|thumb|[[Bow shock]] formed by the [[magnetosphere]] of the young star [[LL Orionis]] (center) as it collides with the [[Orion Nebula]] flow|alt=Patchy orange and blue nebulosity against a black background, with a curved orange arc wrapping around a star at the center.]]

Interstellar space is the physical space outside of the bubbles of plasma known as [[astrosphere]]s, formed by [[stellar wind]]s originating from individual stars, or formed by solar wind emanating from the Sun.<ref name=jpl_interstellarspace /> It is the space between the stars or [[stellar systems]] within a nebula or galaxy.<ref name=Cooper_2023/> Interstellar space contains an [[interstellar medium]] of sparse matter and radiation. The boundary between an astrosphere and interstellar space is known as an [[astropause]]. For the Sun, the astrosphere and astropause are called the heliosphere and heliopause, respectively.<ref name=Garcia-Sage_et_al_2023/>

Approximately 70% of the mass of the interstellar medium consists of lone hydrogen atoms; most of the remainder consists of helium atoms. This is enriched with trace amounts of heavier atoms formed through [[stellar nucleosynthesis]]. These atoms are ejected into the interstellar medium by stellar winds or when evolved stars begin to shed their outer envelopes such as during the formation of a [[planetary nebula]].<ref name="Ferrière2001"/> The cataclysmic explosion of a [[supernova]] propagates [[shock waves]] of stellar ejecta outward, distributing it throughout the interstellar medium, including the heavy elements previously formed within the star's core.<ref name="witt2001"/> The density of matter in the interstellar medium can vary considerably: the average is around 10<sup>6</sup> particles per m<sup>3</sup>,<ref name=Boulares1990/> but cold [[molecular clouds]] can hold 10<sup>8</sup>–10<sup>12</sup> per m<sup>3</sup>.{{sfn|Prialnik|2000|pp=195–196}}<ref name="Ferrière2001"/>

A [[List of interstellar and circumstellar molecules|number of molecules]] exist in interstellar space, which can form dust particles as tiny as 0.1&nbsp;[[Micrometre|μm]].{{sfn|Rauchfuss|2008|pp=72–81}} The tally of molecules discovered through [[radio astronomy]] is steadily increasing at the rate of about four new species per year. Large regions of higher density matter known as molecular clouds allow chemical reactions to occur, including the formation of organic polyatomic species. Much of this chemistry is driven by collisions. Energetic cosmic rays penetrate the cold, dense clouds and ionize hydrogen and helium, resulting, for example, in the [[trihydrogen cation]]. An ionized helium atom can then split relatively abundant [[carbon monoxide]] to produce ionized carbon, which in turn can lead to organic chemical reactions.<ref name="PNAS103_33_12232"/>

The local interstellar medium is a region of space within 100&nbsp;[[parsec|pc]] of the Sun, which is of interest both for its proximity and for its interaction with the Solar System. This volume nearly coincides with a region of space known as the [[Local Bubble]], which is characterized by a lack of dense, cold clouds. It forms a cavity in the [[Orion Arm]] of the Milky Way Galaxy, with dense molecular clouds lying along the borders, such as those in the [[constellation]]s of [[Ophiuchus]] and [[Taurus (constellation)|Taurus]]. The actual distance to the border of this cavity varies from 60 to 250&nbsp;pc or more. This volume contains about 10<sup>4</sup>–10<sup>5</sup> stars and the local interstellar gas counterbalances the [[Stellar-wind bubble|astrospheres]] that surround these stars, with the volume of each sphere varying depending on the local density of the interstellar medium. The Local Bubble contains dozens of warm interstellar clouds with temperatures of up to 7,000&nbsp;K and radii of 0.5–5&nbsp;pc.<ref name=redfield2006/>

When stars are moving at sufficiently high [[peculiar velocities]], their astrospheres can generate [[bow shock]]s as they collide with the interstellar medium. For decades it was assumed that the Sun had a bow shock. In 2012, data from [[Interstellar Boundary Explorer|Interstellar Boundary Explorer (IBEX)]] and NASA's [[Voyager program|Voyager]] probes showed that the Sun's bow shock does not exist. Instead, these authors argue that a [[Mach number|subsonic]] bow wave defines the transition from the solar wind flow to the interstellar medium.<ref name=bow_science/><ref name=bow/> A bow shock is a third boundary characteristic of an astrosphere, lying outside the [[heliosphere#Termination shock|termination shock]] and the astropause.<ref name=bow/>

=== Intergalactic space ===
{{Main|Warm–hot intergalactic medium|Intracluster medium|Intergalactic dust}}
[[File:Structure of the Universe.jpg|thumb|alt=Structure of the Universe|Large-scale matter distribution in a cubic section of the universe. The blue fiber-like structures represent the matter, and the empty regions in between represent the [[cosmic void]]s of the intergalactic medium]]

Intergalactic space is the physical space between galaxies. Studies of the large-scale distribution of galaxies show that the universe has a foam-like structure, with [[Galaxy groups and clusters|groups and clusters of galaxies]] lying along filaments that occupy about a tenth of the total space. The remainder forms [[cosmic void]]s that are mostly empty of galaxies. Typically, a void spans a distance of 7–30 megaparsecs.{{sfn|Wszolek|2013|p=67}}

Surrounding and stretching between galaxies is the [[intergalactic medium]] (IGM). This [[rarefaction|rarefied]] plasma<ref name=jafelice_opher1992/> is organized in a [[galaxy filament|galactic filamentary]] structure.<ref name=wadsley2002/> The diffuse photoionized gas contains filaments of higher density, about one atom per cubic meter,<ref name="Harvard & Smithsonian 2022 k265"/> which is 5–200 times the average density of the universe.<ref name="apj_714_1715"/> The IGM is inferred to be mostly primordial in composition, with 76% hydrogen by mass, and enriched with higher mass elements from high-velocity galactic outflows.<ref name="Oppenheimer_Davé_2006"/>

As gas falls into the intergalactic medium from the voids, it heats up to temperatures of 10<sup>5</sup>&nbsp;K to 10<sup>7</sup>&nbsp;K.<ref name=baas41_908/> At these temperatures, it is called the [[warm–hot intergalactic medium]] (WHIM). Although the plasma is very hot by terrestrial standards, 10<sup>5</sup> K is often called "warm" in astrophysics. Computer simulations and observations indicate that up to half of the atomic matter in the universe might exist in this warm–hot, rarefied state.<ref name="apj_714_1715" /><ref name=ssr134_1_141/><ref name="apjs_182_378"/> When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of 10<sup>8</sup>&nbsp;K and above in the so-called [[intracluster medium]] (ICM).<ref name="apj546_100"/>

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| header            = Overview of different scales of space as [[Location of Earth|regions around Earth]]
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| width1            = 93
| caption1          = [[Earth#Earth–Moon system|Earth-Moon System]]
| image2            = Inner solar system objects top view for wiki.png
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| caption2          = [[Inner Solar System]] with [[Near-Earth object]]s
| image3            = Oort cloud Sedna orbit.svg
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| caption3          = [[Solar&nbsp;System]] and [[Oort cloud]]
| image4            = Angular map of fusors around Sol within 9ly (large).png
| width4            = 93
| caption4          = [[List of nearest stars and brown dwarfs|Nearest stars]]
| image5            = Local Interstellar Clouds with motion arrows.jpg
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| caption5          = [[Local Interstellar Cloud]] and neighbouring [[interstellar medium]]
| image6            = Galaxymap.com, map 100 parsecs (2022).png
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| caption6          = [[List of nearby stellar associations and moving groups|Star association]]s and interstellar medium map of the [[Local Bubble]]
| image7            = Galaxymap.com, map 1000 parsecs (2022).png
| width7            = 93
| caption7          = Molecular clouds around the Sun inside the [[Orion-Cygnus Arm]]
| image8            = OrionSpur.png
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| caption8          = Orion-Cygnus Arm and neighbouring arms
| image9            = Milky Way Arms ssc2008-10.svg
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| caption9          = Orion-Cygnus Arm inside the [[Milky&nbsp;Way]]
| image10            = Milky Way side view.png
| width10            = 93
| caption10          = The Sun within the structure of the Milky&nbsp;Way
| image11           = 06-Local Group (LofE06240).png
| width11           = 93
| caption11         = [[Satellite galaxies of the Milky Way]] in [[Local Group]]
| image12           = 07-Laniakea (LofE07240).png
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| caption12         = [[Virgo Supercluster|Virgo SCl]] in [[Laniakea Supercluster|Laniakea SCl]]
| image13           = Laniakea.gif
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| caption13         = Laniakea SCl in [[Pisces–Cetus Supercluster Complex]]
| image14           = Observable Universe with Measurements 01.png
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| caption14         = [[Observable Universe]] of the [[Universe]]
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