Local Interstellar Cloud

The Solar System is located within a structure called the Local Bubble, a low-density region of the galactic interstellar medium. 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.

{{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

}}

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.

{{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

}}

A recent analysis estimates the Sun will completely exit the LIC in no more than 1,900 years.

{{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

}}

The cloud has a temperature of about {{convert|7000|K|-3|abbr=on}},{{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}} 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.{{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 }}{{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}} In comparison, Earth's atmosphere at the edge of space (i.e. 100 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}}.{{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}}

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

In 2019, researchers found interstellar iron-60 (⁶⁰Fe) in Antarctica, which they relate to the Local Interstellar Cloud.{{cite journal |title=Interstellar ⁶⁰Fe 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 }}

File:Interstellar medium annotated.jpg, 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 picoteslas (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.{{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 |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 }}

The Local Interstellar Cloud's potential effects on Earth are greatly diminished by the solar wind and the Sun's magnetic field. 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.

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• 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

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{{reflist|colwidth=30em}}

• [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}}

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