active asteroid
{{short description|Bodies orbiting within the main asteroid belt which have shown cometary activity}}
File:596 Scheila, 5 minute exposure, Dec. 12, 2010.jpg displaying a comet-like appearance on 12 December 2010]]
File:Aftermath of DART Collision with Dimorphos Captured_by_SOAR_Telescope (noirlab2223a).jpg's impact on the asteroid moon Dimorphos, as seen by the Southern Astrophysical Research Telescope in 2022]]
Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics.{{cite news |last=Andrews |first=Robin George |title=The Mysterious Comets That Hide in the Asteroid Belt - Comets normally fly in from the far reaches of space. Yet astronomers have found them seemingly misplaced in the asteroid belt. Why are they there? |url=https://www.nytimes.com/2022/11/18/science/comet-asteroid-belt-space.html |date=18 November 2022 |work=The New York Times |accessdate=18 November 2022 }} That is, they show a coma, tail, or other visual evidence of mass-loss (like a comet), but their orbits remain within Jupiter's orbit (like an asteroid). These bodies were originally designated main-belt comets (MBCs) in 2006 by astronomers David Jewitt and Henry Hsieh, but this name implies they are necessarily icy in composition like a comet and that they only exist within the main-belt, whereas the growing population of active asteroids shows that this is not always the case.{{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 }}{{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 }}{{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}}
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 Elst and Guido Pizarro in 1996 and given the cometary designation 133P/Elst-Pizarro.{{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=January 20, 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}}
Orbits
Unlike comets, which spend most of their orbit at Jupiter-like or greater distances from the Sun, active asteroids follow orbits within the orbit of Jupiter that are often indistinguishable from the orbits of standard asteroids. Jewitt defines active asteroids as those bodies that, in addition to having visual evidence of mass loss, have an orbit with:
- semi-major axis a < aJupiter (5.20 AU)
- Tisserand parameter with respect to Jupiter TJ > 3.08
Jewitt chooses 3.08 as the Tisserand parameter to separate asteroids and comets instead of 3.0 (the Tisserand parameter of Jupiter itself) to avoid ambiguous cases caused by the real Solar System deviating from an idealized restricted three-body problem.
The first three identified active asteroids all orbit within the outer part of the asteroid belt.{{cite web|date=May 2010 |title=Main Belt Comets |publisher=Hawaii |author=Henry H. Hsieh |url=http://www.ifa.hawaii.edu/~hsieh/mbcs.shtml |archive-url=https://web.archive.org/web/20110806021852/http://www.ifa.hawaii.edu/~hsieh/mbcs.shtml |url-status=dead |archive-date=2011-08-06 |access-date=2010-12-15 }} [http://star.pst.qub.ac.uk/~hhh/mbcs.shtml (older 2010 site)] {{webarchive|url=https://web.archive.org/web/20090810052739/http://star.pst.qub.ac.uk/~hhh/mbcs.shtml |date=2009-08-10 }}
Activity
File:14060-Asteroid-P2013R3-Disintegration-20140306.jpg observed by the Hubble Space Telescope (6 March 2014).{{cite web |last1=Harrington |first1=J.D. |last2=Villard |first2=Ray |title=RELEASE 14-060 NASA's Hubble Telescope Witnesses Asteroid's Mysterious Disintegration |url=http://www.nasa.gov/press/2014/march/nasas-hubble-telescope-witnesses-asteroids-mysterious-disintegration-1 |date=6 March 2014 |work=NASA |access-date=6 March 2014 }}{{cite news|title=Hubble witnesses an asteroid mysteriously disintegrating|url=http://www.spacetelescope.org/news/heic1405/|access-date=12 March 2014|newspaper=ESA / HUBBLE}}]]
Some active asteroids display a cometary dust tail only for a part of their orbit near perihelion. This strongly suggests that volatiles at their surfaces are sublimating, driving off the dust.[https://ac.els-cdn.com/S0273117718301741/1-s2.0-S0273117718301741-main.pdf?_tid=60729ad6-8e38-4774-a5a4-cb1535560808&acdnat=1523207512_194ea87998b5bd4a360bee5af6739f73 The proposed Caroline ESA M3 mission to a Main Belt Comet]. Geraint H. Jones, Jessica Agarwal, Neil Bowles, Mark Burchell, Andrew J. Coates, Alan Fitzsimmons, Amara Graps, Henry H. Hsieh, Carey M. Lisse, Stephen C. Lowry, Adam Masters, Colin Snodgrass, Cecilia Tubiana. Advances in Space Research. 25 February 2018. {{doi|10.1016/j.asr.2018.02.032}} Activity in 133P/Elst–Pizarro is recurrent, having been observed at each of the last three perihelia. The activity persists for a month or several out of each 5-6 year orbit, and is presumably due to ice being uncovered by minor impacts in the last 100 to 1000 years. These impacts are suspected to excavate these subsurface pockets of volatile material helping to expose them to solar radiation.
When discovered in January 2010, P/2010 A2 (LINEAR) was initially given a cometary designation and thought to be showing comet-like sublimation,[http://www.minorplanetcenter.org/mpec/K10/K10A51.html MPEC 2010-A51 : COMET P/2010 A2 (LINEAR)] but P/2010 A2 is now thought to be the remnant of an asteroid-on-asteroid impact.{{cite journal | last1 = Jewitt | first1 = David | last2 = Weaver | first2 = Harold | last3 = Agarwal | first3 = Jessica | last4 = Mutchler | first4 = Max | last5 = Drahus | first5 = Michal | title = A recent disruption of the main-belt asteroid P/2010?A2 | journal = Nature | volume = 467 | pages = 817–9 | date = 2010 | doi = 10.1038/nature09456|bibcode = 2010Natur.467..817J | issue=7317 | pmid=20944743| s2cid = 205222567 }}{{cite journal | last1 = Snodgrass | first1 = Colin | last2 = Tubiana | first2 = Cecilia | last3 = Vincent | first3 = Jean-Baptiste | last4 = Sierks | first4 = Holger | last5 = Hviid | first5 = Stubbe | last6 = Moissl | first6 = Richard | last7 = Boehnhardt | first7 = Hermann | last8 = Barbieri | first8 = Cesare | last9 = Koschny | first9 = Detlef | last10 = Lamy | first10 = Philippe | last11 = Rickman | first11 = Hans | last12 = Rodrigo | first12 = Rafael | last13 = Carry | first13 = Benoît | last14 = Lowry | first14 = Stephen C. | last15 = Laird | first15 = Ryan J. M. | last16 = Weissman | first16 = Paul R. | last17 = Fitzsimmons | first17 = Alan | last18 = Marchi | first18 = Simone | last19 = a’Hearn | first19 = M. | last20 = Angrilli | first20 = F. | last21 = Barucci | first21 = A. | last22 = Bertaux | first22 = J.-L. | last23 = Cremonese | first23 = G. | last24 = Da Deppo | first24 = V. | last25 = Davidsson | first25 = B. | last26 = Debei | first26 = S. | last27 = De Cecco | first27 = M. | last28 = Fornasier | first28 = S. | last29 = Gutiérrez | first29 = P. | last30 = Ip | first30 = W.-H. | title = A collision in 2009 as the origin of the debris trail of asteroid P/2010?A2 | journal = Nature | volume = 467 | pages = 814–6 | date = 2010 | doi = 10.1038/nature09453 | pmid=20944742 | issue=7317| display-authors = 8 |arxiv = 1010.2883 |bibcode = 2010Natur.467..814S | s2cid = 4330570 }} Observations of 596 Scheila indicated that large amounts of dust were kicked up by the impact of another asteroid of approximately 35 meters in diameter.
=P/2013 R3=
{{Main article|P/2013 R3 (Catalina–PanSTARRS)}}
P/2013 R3 (Catalina–PanSTARRS) was discovered independently by two observers by Richard E. Hill using the Catalina Sky Survey's 0.68-m Schmidt telescope and by Bryce T. Bolin using the 1.8-m Pan-STARRS1 telescope on Haleakala.{{cite journal|first1=R|last1=Hill|first2=B |last2=Bolin|first3=J |last3=Kleyna|first4=L |last4=Denneau|first5=R |last5=Wainscoat|first6=M |last6=Micheli|first7=J |last7=Armstrong|first8=M |last8=Molina|first9=H |last9=Sato|title=CBET #3658 : COMET P/2013 R3 (CATALINA-PANSTARRS)|journal=Central Bureau Electronic Telegrams|year=2013|issue=3658|page=1|url=https://ui.adsabs.harvard.edu/abs/2013CBET.3658....1H/abstract|publisher=Central Bureau for Astronomical Telegrams|bibcode=2013CBET.3658....1H|access-date=27 September 2013}} The discovery images taken by Pan-STARRS1 showed the appearance of two distinct sources within 3" of each other combined with a tail enveloping both sources. In October 2013, follow-up observations of P/2013 R3, taken with the 10.4 m Gran Telescopio Canarias on the island of La Palma, showed that this comet was breaking apart.{{cite web|first=Javier|last=Licandro|title=Main Belt Comet P/2013 R3 is breaking apart|url=http://www.iac.es/divulgacion.php?op1=16&id=816&lang=en&img=1051|publisher=IAC Press Release|access-date=17 October 2013}} Inspection of the stacked CCD images obtained on October 11 and 12 showed that the main-belt comet presented a central bright condensation that was accompanied on its movement by three more fragments, A, B, C. The brightest A fragment was also detected at the reported position in CCD images obtained at the 1.52 m telescope of the Sierra Nevada Observatory in Granada on October 12.
NASA reported on a series of images taken by the Hubble Space Telescope between October 29, 2013, and January 14, 2014, that show the increasing separation of the four main bodies.{{Cite web | url=https://science.nasa.gov/science-news/science-at-nasa/2014/06mar_asteroid/ |title = Hubble Witnesses Asteroid's Mysterious Disintegration | Science Mission Directorate}} The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, caused by sunlight, increased the spin rate until the centrifugal force caused the rubble pile to separate.
=Dimorphos=
{{Main|Dimorphos}}
By smashing into the asteroid moon of the binary asteroid 65803 Didymos, NASA's Double Asteroid Redirection Test spacecraft made Dimorphos 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.{{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}}{{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 |language=en |issn=1476-4687 |display-authors=3}} Observations show that Dimorphos lost approximately 1 million kilograms after the collision.{{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 |language=en|url-access=subscription }} Impact produced a dust plume that temporarily brightened the Didymos system and developed a {{convert|10000|km|mi|adj=on|sp=us}}-long dust tail that persisted for several months.{{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}}{{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}}{{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 }} The DART impact is predicted to have caused global resurfacing and deformation of Dimorphos's shape, leaving an impact crater several tens of meters in diameter.{{cite journal
|first1 = Sabina D. |last1 = Raducan
|first2 = Jutzi |last2 = Martin
|title = Global-scale Reshaping and Resurfacing of Asteroids by Small-scale Impacts, with Applications to the DART and Hera Missions
|journal = The Planetary Science Journal
|date = July 2022
|volume = 3
|issue = 6
|id = 128
|pages = 15
|doi-access = free
|doi = 10.3847/PSJ/ac67a7
|bibcode = 2022PSJ.....3..128R
|s2cid = 249268810}}{{cite journal
|display-authors = etal
|first1 = Ryota |last1 = Nakano
|first2 = Masatoshi |last2 = Hirabayashi
|first3 = M. |last3 = Brozovic
|first4 = M. C. |last4 = Nolan
|first5 = S. J. |last5 = Ostro
|first6 = J. L. |last6 = Margot
|title = NASA's Double Asteroid Redirection Test (DART): Mutual Orbital Period Change Due to Reshaping in the Near-Earth Binary Asteroid System (65803) Didymos
|journal = The Planetary Science Journal
|date = July 2022
|volume = 3
|issue = 7
|id = 148
|pages = 16
|doi-access = free
|doi = 10.3847/PSJ/ac7566
|bibcode = 2022PSJ.....3..148N
|s2cid = 250327233|hdl = 11311/1223308
|hdl-access = free
|display-authors = etal
|first1 = S. D. |last1 = Raducan
|first2 = M. |last2 = Jutzi
|first3 = Y. |last3 = Zhang
|first4 = A. F. |last4 = Cheng
|first5 = G. S. |last5 = Collins
|first6 = T. M. |last6 = Davison
|title =Low Strength of Asteroid Dimorphos As Demonstrated by the Dart Impact
|url = https://www.hou.usra.edu/meetings/lpsc2023/pdf/2033.pdf
|conference = 54th Lunar and Planetary Science Conference 2023
|publisher = Lunar and Planetary Institute
|date = March 2023
|issue = 2033
|accessdate = 4 February 2023}} The impact has likely sent Dimorphos into a chaotically tumbling rotation that will subject the moon to irregular tidal forces by Didymos before it will eventually return to a tidally locked state within several decades.{{cite journal
|display-authors = etal
|first1 = Harrison F. |last1 = Agrusa
|first2 = Ioannis |last2 = Gkolias
|first3 = Kleomenis |last3 = Tsiganis
|first4 = Derek C. |last4 = Richardson
|first5 = Alex J. |last5 = Meyer
|first6 = Daniel J. |last6 = Scheeres
|title = The excited spin state of Dimorphos resulting from the DART impact
|journal = Icarus
|date = December 2021
|volume = 370
|id = 114624
|pages = 39
|doi = 10.1016/j.icarus.2021.114624
|arxiv = 2107.07996
|bibcode = 2021Icar..37014624A
|s2cid = 236033921}}{{cite journal
|display-authors = etal
|first1 = Derek C. |last1 = Richardson
|first2 = Harrison F. |last2 = Agrusa
|first3 = Brent |last3 = Barbee
|first4 = William F.|last4 = Bottke
|first5 = Andrew F. |last5 = Cheng
|first6 = Siegfried |last6 = Eggl
|title = Predictions for the Dynamical States of the Didymos System before and after the Planned DART Impact
|journal = The Planetary Science Journal
|date = July 2022
|volume = 3
|issue = 7
|id = 157
|pages = 23
|doi-access = free
|doi = 10.3847/PSJ/ac76c9
|arxiv = 2207.06998
|bibcode = 2022PSJ.....3..157R
|s2cid = 249268465}}{{cite conference
|display-authors = etal
|first1 = A. J. |last1 = Meyer
|first2 = G. |last2 = Noiset
|first3 = Ö. |last3 = Karatekin
|first4 = J. |last4 = McMahon
|first5 = H. F. |last5 = Agrusa
|first6 = R. |last6 = Nakano
|title = Tidal Dissipation in Didymos Following the DART Impact
|url = https://www.hou.usra.edu/meetings/lpsc2023/pdf/2105.pdf
|conference = 54th Lunar and Planetary Science Conference 2023
|publisher = Lunar and Planetary Institute
|date = March 2023
|issue = 2105
|accessdate = 4 February 2023}}
Composition
Some active asteroids show signs that they are icy in composition like a traditional comet, while others are known to be rocky like an asteroid. It has been hypothesized that main-belt comets may have been the source of Earth's water, because the deuterium–hydrogen ratio of Earth's oceans is too low for classical comets to have been the principal source.[http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html Main-Belt Comets May Have Been Source Of Earths Water], Space Daily, Mar 23, (2006). European scientists have proposed a sample-return mission from a MBC called Caroline to analyse the content of volatiles and collect dust samples.
List
Identified members of this morphology class (TJup>3.08) include:{{cite book |editor-first1=K.|editor-last1=Meech|editor-first2=M.|editor-last2=Combi|chapter=The Asteroid-Comet Continuum|first1=David|last1=Jewitt|first2=Henry|last2=Hsieh|year=2022|title=Comets III|pages=34|publisher=University of Arizona Press|arxiv=2203.01397|bibcode=2022arXiv220301397J}}{{rp|page=17}}
Exploration
File:PIA23554-AsteroidBennu-EjectingParticles-20190106.jpg seen ejecting particles on January 6, 2019, in images taken by the OSIRIS-REx spacecraft]]
Castalia is a proposed mission concept for a robotic spacecraft to explore 133P/Elst–Pizarro and make the first in situ measurements of water in the asteroid belt, and thus, help solve the mystery of the origin of Earth's water.{{cite journal|doi=10.1016/j.asr.2017.09.011|title=The Castalia mission to Main Belt Comet 133P/Elst-Pizarro|journal=Advances in Space Research|volume=62|issue=8|pages=1947–1976|year=2018|last1=Snodgrass|first1=C.|last2=Jones|first2=G.H.|last3=Boehnhardt|first3=H.|last4=Gibbings|first4=A.|last5=Homeister|first5=M.|last6=Andre|first6=N.|last7=Beck|first7=P.|last8=Bentley|first8=M.S.|last9=Bertini|first9=I.|last10=Bowles|first10=N.|last11=Capria|first11=M.T.|last12=Carr|first12=C.|last13=Ceriotti|first13=M.|last14=Coates|first14=A.J.|last15=Della Corte|first15=V.|last16=Donaldson Hanna|first16=K.L.|last17=Fitzsimmons|first17=A.|last18=Gutiérrez|first18=P.J.|last19=Hainaut|first19=O.R.|last20=Herique|first20=A.|last21=Hilchenbach|first21=M.|last22=Hsieh|first22=H.H.|last23=Jehin|first23=E.|last24=Karatekin|first24=O.|last25=Kofman|first25=W.|last26=Lara|first26=L.M.|last27=Laudan|first27=K.|last28=Licandro|first28=J.|last29=Lowry|first29=S.C.|last30=Marzari|first30=F.|display-authors=29|bibcode=2018AdSpR..62.1947S|arxiv=1709.03405|s2cid=55821241}} The lead is Colin Snodgrass, from The Open University in the UK. Castalia was proposed in 2015 and 2016 to the European Space Agency within the Cosmic Vision programme missions M4 and M5, but it was not selected. The team continues to mature the mission concept and science objectives. Because of the construction time required and orbital dynamics, a launch date of October 2028 was proposed.
On January 6, 2019, the OSIRIS-REx mission first observed episodes of particle ejection from 101955 Bennu shortly after entering orbit around the near-Earth asteroid, leading it to be newly classified as an active asteroid and marking the first time that asteroid activity had been observed up close by a spacecraft. It has since observed at least 10 other such events. The scale of these observed mass loss events is much smaller than those previously observed at other active asteroids by telescopes, indicating that there is a continuum of mass loss event magnitudes at active asteroids.{{cite journal|title = Episodes of particle ejection from the surface of the active asteroid (101955) Bennu|first1 = D. S. | last1 = Lauretta| first2 = C. W. |last2 = Hergenrother | first3 = S. R. | last3 = Chesley | first4 = J. M. | last4 = Leonard | first5 = J. Y. | last5 = Pelgrift | first6 = C. D. | last6 = Adam | first7 = M. | last7 = Al Asad|display-authors=5| journal = Science | date = 6 Dec 2019| volume = 366 | issue = 6470 |pages = eaay3544 | doi = 10.1126/science.aay3544 |pmid = 31806784 |bibcode = 2019Sci...366.3544L |s2cid = 208764910 |url = http://oro.open.ac.uk/68479/1/Lauretta_et_al_2019_accepted.pdf | doi-access = free }}
See also
References
{{reflist}}
External links
- [http://asteroids.matf.bg.ac.rs/fam/properelements.php Proper elements of active asteroids at Asteroid Families Portal]
- Henry Hsieh's [https://web.archive.org/web/20111026205513/http://www.ifa.hawaii.edu/users/hsieh/mbcs.shtml Main-Belt Comets] page has extensive details on Main-belt comets
- [http://www2.ess.ucla.edu/~jewitt/mbc.html David Jewitt. The Active Asteroids]
- [https://web.archive.org/web/20070501211319/http://www.planetary.org/blog/article/00000551/ Planetary Society article on MBCs]
- [http://www.centauri-dreams.org/?p=601 Discussion of possible differences in characteristics of the water in MBCs and other comets]
- YouTube [https://www.youtube.com/watch?v=B1W4NTmI5Bk Interview with David Jewitt] (discussion on main-belt comets starts around 9 minutes into video)
- [http://www2.ess.ucla.edu/~jewitt/images/Impact_Trigger_sketch.jpg Impact trigger mechanism] diagram by David Jewitt
- [http://remanzacco.blogspot.com/2010/12/comet-like-appearance-of-596-scheila.html Comet-like appearance of (596) Scheila]
- [https://web.archive.org/web/20110719023715/http://asteroidi.uai.it/t3.htm Project T3: Finding Comets in the Asteroid Population]
- {{cite journal |arxiv=1112.5220|doi=10.1088/0004-6256/143/3/66|bibcode=2012AJ....143...66J|title=The Active Asteroids|year=2012|last1=Jewitt|first1=David|journal=The Astronomical Journal|volume=143|issue=3|pages=66|s2cid=45208650}}
- {{cite journal |arxiv=1202.2126|doi=10.1088/2041-8205/748/1/L15|bibcode=2012ApJ...748L..15H|title=DISCOVERY OF MAIN-BELT COMET P/2006 VW 139 BY Pan-STARRS1|year=2012|last1=Hsieh|first1=Henry H.|last2=Yang|first2=Bin|last3=Haghighipour|first3=Nader|last4=Kaluna|first4=Heather M.|last5=Fitzsimmons|first5=Alan|last6=Denneau|first6=Larry|last7=Novaković|first7=Bojan|last8=Jedicke|first8=Robert|last9=Wainscoat|first9=Richard J.|last10=Armstrong|first10=James D.|last11=Duddy|first11=Samuel R.|last12=Lowry|first12=Stephen C.|last13=Trujillo|first13=Chadwick A.|last14=Micheli|first14=Marco|last15=Keane|first15=Jacqueline V.|last16=Urban|first16=Laurie|last17=Riesen|first17=Timm|last18=Meech|first18=Karen J.|last19=Abe|first19=Shinsuke|last20=Cheng|first20=Yu-Chi|last21=Chen|first21=Wen-Ping|last22=Granvik|first22=Mikael|last23=Grav|first23=Tommy|last24=Ip|first24=Wing-Huen|author-link24= Ip Wing-huen|last25=Kinoshita|first25=Daisuke|last26=Kleyna|first26=Jan|last27=Lacerda|first27=Pedro|last28=Lister|first28=Tim|last29=Milani|first29=Andrea|last30=Tholen|first30=David J.|journal=The Astrophysical Journal|volume=748|issue=1|pages=L15|s2cid=8693844|display-authors=29}}
- [http://remanzacco.blogspot.it/2012/10/new-comet-p2012-t1-panstarrs.html New Comet: P/2012 T1 (PANSTARRS)] (Remanzacco Observatory : 16 Oct 2012)
- {{cite journal |arxiv=1305.2621|doi=10.1093/mnras/stt839|bibcode=2013MNRAS.434.1821F|title=The location of Asteroidal Belt Comets (ABCs), in a comet's evolutionary diagram: The Lazarus Comets|year=2013|last1=Ferrín|first1=Ignacio|last2=Zuluaga|first2=Jorge|last3=Cuartas|first3=Pablo|journal=Monthly Notices of the Royal Astronomical Society|volume=434|issue=3|pages=1821–1837|doi-access=free |s2cid=118177774}}
- [http://www.iac.es/divulgacion.php?op1=16&id=816&lang=en P/2013 R3: a Main Belt Comet that is breaking apart. J. Licandro] New images obtained with the GTC
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