Editing Asteroid (section)

=== Active asteroids ===
{{Main|Active asteroid}}[[File:PIA23554-AsteroidBennu-EjectingParticles-20190106.jpg|thumb|Asteroid {{ats|101955|Bennu}} seen ejecting particles by the [[OSIRIS-REx]]]]

Active asteroids are objects that have asteroid-like orbits but show [[comet]]-like visual characteristics. That is, they show [[Coma (cometary)|comae]], [[comet tail|tails]], or other visual evidence of mass-loss (like a comet), but their orbit remains within [[Jupiter]]'s orbit (like an asteroid).<ref name="Jewitt" /><ref name="JHA15">{{cite book|chapter=The Active Asteroids|first1=David|last1=Jewitt|first2=Henry|last2=Hsieh|first3=Jessica|last3=Agarwal|year=2015|title= Asteroids IV|pages=221–241| editor1-last =  Michel| editor1-first = P. | editor2-last = others| display-editors = 1 | publisher=[[University of Arizona]]|doi= 10.2458/azu_uapress_9780816532131-ch012 |arxiv=1502.02361|bibcode=2015aste.book..221J|isbn=978-0-8165-3213-1|s2cid=119209764| chapter-url= http://www2.ess.ucla.edu/~jewitt/papers/2015/JHA15.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www2.ess.ucla.edu/~jewitt/papers/2015/JHA15.pdf |archive-date=2022-10-09 |url-status=live |access-date=2020-01-30}}</ref> These bodies were originally designated '''main-belt comets''' (MBCs) in 2006 by astronomers [[David Jewitt]] and [[Henry Hsieh (astronomer)|Henry Hsieh]], but this name implies they are necessarily icy in composition like a comet and that they only exist within the [[asteroid belt|main-belt]], whereas the growing population of active asteroids shows that this is not always the case.<ref name="Jewitt">{{cite web |title=The Active Asteroids |publisher=[[UCLA]], Department of Earth and Space Sciences |author=David Jewitt |url=http://www2.ess.ucla.edu/~jewitt/mbc.html |access-date=2020-01-26|author-link=David Jewitt }}</ref><ref name="NYT-20190319">{{cite news |last1=Chang |first1=Kenneth |last2=Stirone |first2=Shannon |title=The Asteroid Was Shooting Rocks Into Space. 'Were We Safe in Orbit?' – NASA's Osiris-Rex and Japan's Hayabusa2 spacecraft reached the space rocks they are surveying last year, and scientists from both teams announced early findings on Tuesday (03/19/2019) |url=https://www.nytimes.com/2019/03/19/science/bennu-ryugu-asteroids.html |date=19 March 2019 |work=[[The New York Times]] |access-date=21 March 2019 }}</ref><ref>{{cite web |title=Hubble Observes Six Tails from an Unusual Asteroid|date=14 November 2013 |publisher=Space Telescope Science Institute (STScI), official YouTube channel for the Hubble Space Telescope|url=https://www.youtube.com/watch?v=CGgRNWUFfZ0  |archive-url=https://ghostarchive.org/varchive/youtube/20211222/CGgRNWUFfZ0 |archive-date=2021-12-22 |url-status=live|access-date=2014-11-15}}{{cbignore}}</ref>

The first active asteroid discovered is [[7968 Elst–Pizarro]]. It was discovered (as an asteroid) in 1979 but then was found to have a tail by [[Eric Walter Elst|Eric Elst]] and Guido Pizarro in 1996 and given the cometary designation 133P/Elst-Pizarro.<ref name="Jewitt"/><ref name=HH133P>{{cite web|last=Hsieh|first=Henry|title=133P/Elst-Pizarro|url=http://www.ifa.hawaii.edu/~hsieh/elstpiz.shtml|publisher=UH Institute for Astronomy|access-date=22 June 2012|date=20 January 2004|url-status=dead|archive-url=https://web.archive.org/web/20111026205338/http://www.ifa.hawaii.edu/~hsieh/elstpiz.shtml|archive-date=26 October 2011}}</ref> Another notable object is [[311P/PanSTARRS]]: observations made by the [[Hubble Space Telescope]] revealed that it had six comet-like tails.<ref name="hubblesite">{{cite web|title=NASA's Hubble Sees Asteroid Spouting Six Comet-Like Tails|url=http://hubblesite.org/newscenter/archive/releases/2013/52/text/|publisher=Hubblesite|date=7 November 2013}}</ref> The tails are suspected to be streams of material ejected by the asteroid as a result of a [[rubble pile]] asteroid spinning fast enough to remove material from it.<ref name=Jewitt2013>{{cite journal
 |last1=Jewitt |first1=D.
 |last2=Agarwal |first2=J.
 |last3=Weaver |first3=H.
 |last4=Mutchler |first4=M.
 |last5=Larson |first5=S.
 |year=2013
 |title=The Extraordinary Multi-Tailed Main-Belt Comet P/2013 P5
 |journal=[[The Astronomical Journal]]
 |volume= 778|issue= 1|pages=L21
 |arxiv=1311.1483
 |bibcode=2013ApJ...778L..21J
 |doi=10.1088/2041-8205/778/1/L21
|s2cid=67795816
 }}</ref>

[[File:Hubble view of Dimorphos ejecta (October 8).png|thumb|Dimorphos and the tail created after the DART impact, photo by the Hubble Space Telescope]]

By smashing into the asteroid [[Dimorphos]], NASA's [[Double Asteroid Redirection Test]] spacecraft made it an active asteroid. Scientists had proposed that some active asteroids are the result of impact events, but no one had ever observed the activation of an asteroid. The DART mission activated Dimorphos under precisely known and carefully observed impact conditions, enabling the detailed study of the formation of an active asteroid for the first time.<ref name="nasa-march2023">{{cite web |last1=Furfaro |first1=Emily |title=NASA's DART Data Validates Kinetic Impact as Planetary Defense Method |url=https://www.nasa.gov/feature/nasa-s-dart-data-validates-kinetic-impact-as-planetary-defense-method |website=NASA |access-date=9 March 2023 |date=28 February 2023}} {{PD-notice}}</ref><ref>{{cite journal |last1=Li |first1=Jian-Yang |last2=Hirabayashi |first2=Masatoshi |last3=Farnham |first3=Tony L. |last4=Sunshine |first4=Jessica M. |last5=Knight |first5=Matthew M. |last6=Tancredi |first6=Gonzalo |last7=Moreno |first7=Fernando |last8=Murphy |first8=Brian |last9=Opitom |first9=Cyrielle |last10=Chesley |first10=Steve |last11=Scheeres |first11=Daniel J. |last12=Thomas |first12=Cristina A. |last13=Fahnestock |first13=Eugene G. |last14=Cheng |first14=Andrew F. |last15=Dressel |first15=Linda |last16=Ernst |first16=Carolyn M. |last17=Ferrari |first17=Fabio |last18=Fitzsimmons |first18=Alan |last19=Ieva |first19=Simone |last20=Ivanovski |first20=Stavro L. |last21=Kareta |first21=Teddy |last22=Kolokolova |first22=Ludmilla |last23=Lister |first23=Tim |last24=Raducan |first24=Sabina D. |last25=Rivkin |first25=Andrew S. |last26=Rossi |first26=Alessandro |last27=Soldini |first27=Stefania |last28=Stickle |first28=Angela M. |last29=Vick |first29=Alison |last30=Vincent |first30=Jean-Baptiste |last31=Weaver |first31=Harold A. |last32=Bagnulo |first32=Stefano |last33=Bannister |first33=Michele T. |last34=Cambioni |first34=Saverio |last35=Bagatin |first35=Adriano Campo |last36=Chabot |first36=Nancy L. |last37=Cremonese |first37=Gabriele |last38=Daly |first38=R. Terik |last39=Dotto |first39=Elisabetta |last40=Glenar |first40=David A. |last41=Granvik |first41=Mikael |last42=Hasselmann |first42=Pedro H. |last43=Herreros |first43=Isabel |last44=Jacobson |first44=Seth |last45=Jutzi |first45=Martin |last46=Kohout |first46=Tomas |last47=La Forgia |first47=Fiorangela |last48=Lazzarin |first48=Monica |last49=Lin |first49=Zhong-Yi |last50=Lolachi |first50=Ramin |last51=Lucchetti |first51=Alice |last52=Makadia |first52=Rahil |last53=Epifani |first53=Elena Mazzotta |last54=Michel |first54=Patrick |last55=Migliorini |first55=Alessandra |last56=Moskovitz |first56=Nicholas A. |last57=Ormö |first57=Jens |last58=Pajola |first58=Maurizio |last59=Sánchez |first59=Paul |last60=Schwartz |first60=Stephen R. |last61=Snodgrass |first61=Colin |last62=Steckloff |first62=Jordan |last63=Stubbs |first63=Timothy J. |last64=Trigo-Rodríguez |first64=Josep M. |title=Ejecta from the DART-produced active asteroid Dimorphos |journal=Nature |date=1 March 2023 |volume=616 |issue=7957 |pages=452–456 |doi=10.1038/s41586-023-05811-4 |pmid=36858074 |pmc=10115637 |arxiv=2303.01700 |bibcode=2023Natur.616..452L |s2cid=257282549|issn=1476-4687 |display-authors=3}}</ref> Observations show that Dimorphos lost approximately 1 million kilograms after the collision.<ref>{{cite journal |last1=Witze |first1=Alexandra |title=Asteroid lost 1 million kilograms after collision with DART spacecraft |journal=Nature |date=1 March 2023 |volume=615 |issue=7951 |pages=195 |doi=10.1038/d41586-023-00601-4 |pmid=36859675 |bibcode=2023Natur.615..195W |s2cid=257282080 |url=https://www.nature.com/articles/d41586-023-00601-4 |access-date=9 March 2023}}</ref> Impact produced a dust plume that temporarily brightened the Didymos system and developed a {{convert|10000|km|mi|adj=on|sp=us}}-long [[comet tail|dust tail]] that persisted for several months.<ref name="NOIRLab-20221003">{{cite web
 |title = SOAR Telescope Catches Dimorphos's Expanding Comet-like Tail After DART Impact
 |url = https://noirlab.edu/public/news/noirlab2223/
 |first = Charles |last= Blue
 |publisher = NOIRLab
 |date = 3 October 2022
 |accessdate = 4 February 2023}}</ref><ref name="NASA-20221215">{{cite web
 |title = Early Results from NASA's DART Mission
 |url = https://www.nasa.gov/feature/early-results-from-nasa-s-dart-mission
 |first = Jessica |last= Merzdorf
 |publisher = NASA
 |date = 15 December 2022
 |accessdate = 4 February 2023}}</ref><ref name="Li2023">{{cite journal
  |display-authors = etal
  |first1 = Jian-Yang
  |last1 = Li
  |first2 = Masatoshi
  |last2 = Hirabayashi
  |first3 = Tony
  |last3 = Farnham
  |first4 = Matthew
  |last4 = Knight
  |first5 = Gonzalo
  |last5 = Tancredi
  |first6 = Fernando
  |last6 = Moreno
  |title = Ejecta from the DART-produced active asteroid Dimorphos
  |url = https://assets.researchsquare.com/files/rs-2292349/v1/34562254-db7b-4289-a7ff-238159687528.pdf?c=1669139626
  |journal = Nature
  |date = March 2022
  |volume = 616
  |issue = 7957
  |pages = 452–456
  |doi = 10.1038/s41586-023-05811-4
  |pmid = 36858074
  |pmc = 10115637
  |arxiv = 2303.01700
  |bibcode = 2023Natur.616..452L
  |s2cid = 257282549
  |access-date = 11 March 2023
  |archive-date = 7 March 2023
  |archive-url = https://web.archive.org/web/20230307161053/https://assets.researchsquare.com/files/rs-2292349/v1/34562254-db7b-4289-a7ff-238159687528.pdf?c=1669139626
  |url-status = dead
  }}</ref>