View source for Local Interstellar Cloud

{{Short description|Interstellar cloud in the Milky Way Galaxy}}
{{infobox nebula
|name= Local Interstellar Cloud
|image= Galaxymap.com, map 10 parsecs (2022).png
|caption= Diagram of surrounding stars and artist's conception of the Local Interstellar Cloud
|type= Interstellar cloud
|dimensions = {{convert|30|ly|pc|abbr=on|lk=on}}
|names= Local Cloud, LIC
|constellation=None, [[Solar System]] is inside the nebula<ref name=SIMBAD>{{cite simbad |title=NAME LIC |access-date=March 15, 2014}}</ref>
}}
[[File:The Local Interstellar Cloud and neighboring G-cloud complex.svg|thumb|200px|Map showing the [[Sun]] located near the edge of the Local Interstellar Cloud and [[Alpha Centauri]] about 4 [[light-year]]s away in the neighboring [[G-Cloud]] complex]]

The '''Local Interstellar Cloud''' ('''LIC'''), also known as the '''Local Fluff''', is an [[interstellar cloud]] roughly {{convert|30|ly|pc|1|lk=on}} across, through which the [[Solar System]] is moving. This feature overlaps with a region around the Sun referred to as the '''solar neighborhood'''.<ref>{{cite book | chapter=Solar Neighborhood | year=2011 | title=Encyclopedia of Astrobiology | pages=1526–1527 | display-editors=1 | editor1-first=Muriel | editor1-last=Gargaud | editor2-first=Ricardo | editor2-last=Amils | editor3-first=José Cernicharo | editor3-last=Quintanilla | editor4-first=Henderson James (Jim) | editor4-last=Cleaves II | editor5-first=William M. | editor5-last=Irvine | editor6-first=Daniele L. | editor6-last=Pinti | editor7-first=Michel | editor7-last=Viso | doi=10.1007/978-3-642-11274-4_1460 | isbn=978-3-642-11271-3 | chapter-url=https://link.springer.com/referenceworkentry/10.1007/978-3-642-11274-4_1460 | access-date=2022-07-01 }}</ref> It is unknown whether the [[Sun]] is embedded in the Local Interstellar Cloud, or is in the region where the Local Interstellar Cloud is interacting with the neighboring [[G-Cloud]].<ref name="Gilster-unknown-region">{{cite web |url=http://www.centauri-dreams.org/?p=14203 |title=Into the Interstellar Void |work=Centauri Dreams |first=Paul |last=Gilster |date=September 1, 2010}}</ref> Like the G-Cloud and others, the LIC is part of the [[Interstellar medium|Very Local Interstellar Medium]] which begins where the [[heliosphere]] and [[interplanetary medium]] end,<ref name="Linsky p. ">{{citation | last=Linsky | first=Jeffrey | title=What lies immediately outside of the heliosphere in the very local interstellar medium (VLISM): morphology of the Local Interstellar Cloud, its hydrogen hole, Stromgren Shells, and 60Fe accretion | journal=Egu General Assembly Conference Abstracts | publisher=Copernicus GmbH | date=2020-03-23 | doi=10.5194/egusphere-egu2020-1410 | page=1410| bibcode=2020EGUGA..22.1410L | s2cid=226032795 | doi-access= free}}</ref> the furthest that probes have traveled.

==Structure==
The Solar System is located within a structure called the [[Local Bubble]], a low-density region of the galactic [[interstellar medium]].<ref name="JPL interstellar" />  Within this region is the Local Interstellar Cloud (LIC), an area of slightly higher hydrogen density. It is estimated that the Solar System entered the LIC within the past 10,000 years.<ref name="Frisch-2011-sec4-2-4">
{{cite journal
| vauthors   =  Frisch PC, etal
| date       =  September 2011
| title      = The Interstellar Medium Surrounding the Sun
| url        = https://www.annualreviews.org/doi/10.1146/annurev-astro-081710-102613
| journal    = Annual Review of Astronomy and Astrophysics
| volume     = 49
| issue = 1
| pages      = 252
| doi        = 10.1146/annurev-astro-081710-102613
| bibcode = 2011ARA&A..49..237F
| access-date = 2021-12-28
| url-access= subscription
}}
</ref>
It is uncertain whether the Sun is still inside of the LIC or has already entered a transition zone between the LIC and the G cloud.<ref name="Gilster-unknown-region"/><ref name="Frisch-2011-sec4-2-4" /><ref name="Linsky-2019">
{{cite journal
| vauthors   =  Linsky JL, etal
| date       = November 18, 2019 
| title      = The Interface between the Outer Heliosphere and the Inner Local ISM
| journal    = The Astrophysical Journal
| volume     = 886
| issue      = 1
| pages      = 41
| doi        = 10.3847/1538-4357/ab498a
| arxiv = 1910.01243 
| bibcode = 2019ApJ...886...41L 
| s2cid = 203642080 
| doi-access= free
}}
</ref>
A recent analysis estimates the Sun will completely exit the LIC in no more than 1,900 years.<ref name="Linsky-2020">
{{cite journal
| vauthors   =  Linsky JL, etal
| date       = March 2020
| title      = New results concerning the environment of the heliosphere, nearby interstellar clouds, and physical processes in the inter–cloud medium
| journal    = Journal of Physics: Conference Series
| volume     = 1620
| issue = 1
| pages      = 012010
| doi        = 10.1088/1742-6596/1620/1/012010
| bibcode = 2020JPhCS1620a2010L
| s2cid = 225188522
| doi-access= free
}}
</ref>

The cloud has a temperature of about {{convert|7000|K|-3|abbr=on}},<ref name="near-earth">{{cite web |url=https://science.nasa.gov/science-news/science-at-nasa/2003/06jan_bubble |title=Near-Earth Supernovas |publisher=NASA |series=NASA Science |date=January 6, 2003 |access-date=February 1, 2011}}</ref> about the same temperature as the surface of the Sun. However, its [[specific heat capacity]] is very low because it is not very dense, with {{convert|0.3|/cm3||sigfig=1|adj=pre|atoms}}. This is less dense than the average for the interstellar medium in the [[Milky Way]] ({{convert|0.5|/cm3||abbr=on|disp=or|sigfig=1}}), though six times denser than the gas in the hot, low-density Local Bubble ({{convert|0.05|/cm3||abbr=on|disp=or|sigfig=1}}) which surrounds the local cloud.<ref name="JPL interstellar">{{cite web |url=http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html |title=Our Local Galactic Neighborhood |publisher=NASA |series=Interstellar Probe Project |year=2000 |access-date=2012-08-08 |archive-url=https://web.archive.org/web/20131121061128/http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html |archive-date=2013-11-21 |url-status=dead }}</ref><ref name="Boulanger">{{cite conference |title=Course 7: Dust in the Interstellar Medium |book-title=Infrared Space Astronomy, Today and Tomorrow |conference=Les Houches Physics School. Grenoble, France. August 3–28, 1998. |first1=F. |last1=Boulanger |first2=P. |last2=Cox |first3=A. P. |last3=Jones |editor1-first=F. |editor1-last=Casoli|editor1-link= Fabienne Casoli |editor2-first=J. |editor2-last=Lequeux |editor3-first=F. |editor3-last=David |display-authors=1 |volume=70 |page=251 |year=2000 |bibcode=2000isat.conf..251B}}</ref> In comparison, [[Atmosphere of Earth|Earth's atmosphere]] at [[Kármán line|the edge of space]] (i.e. 100&nbsp;km above sea level) has around 1.2{{e|13}} molecules per cubic centimeter, dropping to around 50 million (5.0{{e|7}}) at {{convert|450|km|mi|0|abbr=on}}.<ref>{{cite book |title=U.S. Standard Atmosphere, 1976 |publisher=[[NOAA]], [[NASA]] and [[U.S. Air Force]] |author=United States Committee on Extension to the Standard Atmosphere |pages=210–215 |date=October 1976 |oclc=3360756}}</ref>

The cloud is flowing outwards from the [[Scorpius–Centaurus association]], a [[stellar association]] that is a star-forming region,<ref name="apod-1">{{Cite APOD |title=The Local Interstellar Cloud |date=February 10, 2002 |access-date=December 21, 2016}}</ref><ref name="apod-2">{{Cite APOD |title=The Local Bubble and the Galactic Neighborhood |date=February 17, 2002 |access-date=December 21, 2016}}</ref> roughly perpendicular to the Sun's own direction.

In 2019, researchers found interstellar [[iron-60]] (<sup>60</sup>Fe) in [[Antarctica]], which they relate to the Local Interstellar Cloud.<ref name="Koll2019">{{cite journal |title=Interstellar <sup>60</sup>Fe in Antarctica |journal=Physical Review Letters |first1=Dominik |last1=Koll |first2=Gunther |last2=Korschinek |first3=Thomas |last3=Faestermann |first4=J. M. |last4=Gómez-Guzmán |first5=Sepp |last5=Kipfstuhl |first6=Silke |last6=Merchel |first7=Jan M. |last7=Welch |display-authors=1 |volume=123 |issue=7 |at=072701 |date=August 2019 |doi=10.1103/PhysRevLett.123.072701 |bibcode=2019PhRvL.123g2701K |pmid=31491090|s2cid=201868513 |hdl=1885/298253 |hdl-access=free }}</ref>

==Interaction with solar magnetic field==
[[File:Interstellar medium annotated.jpg|thumb|upright=2|The Solar System within the [[interstellar medium]], with the different regions and their distances on a logarithmic scale (object sizes not to scale)]]
In 2009, ''[[Voyager 2]]'' data suggested that the magnetic strength of the local interstellar medium was much stronger than expected (370 to 550 [[Pico-|pico]][[tesla (unit)|teslas]] (pT), against previous estimates of 180 to 250 pT). The fact that the Local Interstellar Cloud is strongly magnetized could explain its continued existence despite the pressures exerted upon it by the winds that blew out the Local Bubble.<ref>{{cite journal |url=http://www-personal.umich.edu/~tamas/TIGpapers/2009/2009_Opher_nature.pdf |title=A strong, highly-tilted interstellar magnetic field near the Solar System |journal=[[Nature (journal)|Nature]] |first1=M. |last1=Opher |first2=F. |last2=Alouani Bibi |first3=G. |last3=Toth |first4=J. D. |last4=Richardson |first5=V. V. |last5=Izmodenov |first6=T. I. |last6=Gombosi |display-authors=1 |volume=462 |date=December 24–31, 2009 |issue=7276 |doi=10.1038/nature08567 |bibcode=2009Natur.462.1036O |pages=1036–1038 |pmid=20033043|s2cid=205218936 }}</ref>

The Local Interstellar Cloud's potential effects on Earth are greatly diminished by the [[solar wind]] and the [[Stellar magnetic field|Sun's magnetic field]].<ref name="near-earth" /> This interaction with the [[heliosphere]] is under study by the [[Interstellar Boundary Explorer]] (IBEX), a [[NASA]] satellite mapping the boundary between the Solar System and interstellar space.

==See also==
{{div col|colwidth=30em}}
* [[Gould Belt]]
* [[List of nearest stars and brown dwarfs]]
* [[List of nearby stellar associations and moving groups]]
* [[Orion Arm]]
* [[Perseus Arm]]
* [[Voyager program]] – probes left heliosphere in the 2010s
{{div col end}}

==References==
{{reflist|colwidth=30em}}

==Further reading==
*[https://web.archive.org/web/20100723010447/http://science.nasa.gov/science-news/science-at-nasa/2004/17dec_heliumstream/ "A Breeze from the Stars"] at NASA Science
*[https://science.nasa.gov/science-news/science-at-nasa/2009/23dec_voyager "Voyager Makes an Interstellar Discovery"] at NASA Science
*[http://www.solstation.com/x-objects/chimney.htm "Local Chimney and Superbubbles"]
*{{cite journal |title=Don't stop till you get to the Fluff |journal=New Scientist |first=Mark |last=Anderson |volume=193 |issue=2585 |pages=26–30 |date=January 6, 2007 |doi=10.1016/S0262-4079(07)60043-8}}

==External links==
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[[Category:Local Interstellar Cloud| ]]