7968 Elst–Pizarro

{{Infobox planet

| minorplanet = yes

| background = #D6D6D6

| name = 7968 Elst–Pizarro
133P/Elst–Pizarro

| image = 7968 Elst–Pizarro Eso9637a.jpg

| image_scale =

| caption = {{longitem|7968 Elst–Pizarro imaged at La Silla Observatory in August 1996. The narrow tail is visible.|style=padding: 6px 0; line-height: 1.3em;}}

| discoverer = {{underline|{{mp|1979 OW|7}}}}:
M. R. S. Hawkins
{{nowrap|R. H. McNaught, S. J. Bus}}
{{underline|1996 N2}}:
Eric W. Elst, Guido Pizarro

| discovered = 24 July 1979 ({{mp|1979 OW|7}})
14 July 1996 (1996 N2)

| mpc_name = (7968) Elst–Pizarro

| alt_names = P/1996 N2
{{mp|1979 OW|7}}

| mp_category = Main-belt comet
Main-belt asteroid
Themis/ Beagle family

| orbit_ref =

| epoch = 13 January 2016 (JD 2457400.5)

| semimajor = {{Convert|3.1600|AU|Gm|abbr=on}} (a)

| perihelion = {{Convert|2.6524|AU|Gm|abbr=on}} (q)

| time_periastron = 2024-May-10{{cite web

|title=Horizons Batch for 7968 Elst-Pizarro (1996 N2) on 2024-May-10

|publisher=JPL Horizons

|type=Perihelion occurs when rdot flips from negative to positive

|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27133P%27&START_TIME=%272024-May-10%27&STOP_TIME=%272024-May-11%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27

|accessdate=2023-04-29}} (JPL#70/Soln.date: 2023-Apr-25

| aphelion = {{Convert|3.66751|AU|Gm|abbr=on|lk=on}} (Q)

| eccentricity = 0.16062 (e)

| period = 5.62 yr (2051.7 d)

| inclination = 1.3873° (i)

| asc_node = 160.14° (Ω)

| arg_peri = 131.97° (ω)

| mean_anomaly = 187.70° (M)

| avg_speed = 16.64 km/s

| dimensions = {{cvt|3.8|+/-|0.6|km}}
{{val|3.9|0.4|0.3}} km

| mass =

| density = {{cvt|1.3|g/cm3||adj=mid|(?)}}

| rotation = {{Convert|3.471|h|d|abbr=on|lk=on}}

| spectral_type =

| magnitude = 17.24 to 20.71

| abs_magnitude = 15.7
15.3_R (2004)
15.49_R (2010)

| albedo = 0.074±0.013_R

| single_temperature = 160 K

| mean_motion = {{Deg2DMS|0.17546|sup=ms}} / day (n)

| observation_arc = 13350 days (36.55 yr)

| uncertainty = 0

| jupiter_moid = {{Convert|1.51427|AU|Gm|abbr=on}}

| tisserand = 3.185

}}

Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets, and is the prototype of active asteroids. Its orbit keeps it within the asteroid belt, yet it displayed a dust tail like a comet while near perihelion in 1996, 2001, and 2007.

As a comet it is formally designated 133P/Elst–Pizarro.
As an asteroid it is designated 7968 Elst–Pizarro.

Elst–Pizarro was reported in 1979 as minor planet {{mp|1979 OW|7}},{{cite web |last1=Hsieh |first1=Henry |title=Active Asteroids |url=https://oxfordre.com/planetaryscience/display/10.1093/acrefore/9780190647926.001.0001/acrefore-9780190647926-e-188 |website=Oxford Research Encyclopedias |date=2020 |publisher=Oxford University Press |access-date=3 October 2023 |doi=10.1093/acrefore/9780190647926.013.188 |isbn=978-0-19-064792-6 }} with its image on a photographic plate being completely stellar in appearance. Its orbit remains entirely within the orbits of Mars and Jupiter, with eccentricity 0.165, typical of a minor planet in the asteroid belt. However, the images taken by Eric W. Elst and Guido Pizarro in 1996, when it was near perihelion, clearly show a cometary tail. Since this is not normal behaviour for asteroids, it is suspected that Elst–Pizarro has a different, probably icy, composition. The cometary nature of Elst–Pizarro was first discovered when a linear dust feature was observed with the ESO 1-metre Schmidt telescope at La Silla Observatory on 7 August 1996.{{cite web |url=http://www.eso.org/public/unitedkingdom/news/eso9637/ |title=Strange Comet Discovered at ESO |work=ESO |date=16 September 1996}}

Subsequently, around the next perihelion in November 2001, the cometary activity appeared again, and persisted for 5 months. It again came to perihelion on 8 February 2013. The outgassing was found to happen only on small part of the surface measuring less than {{convert|600|m}} in effective diameter, likely being the relatively recent (younger than 100 million years) impact crater.

At present, seven other objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson–Harrington (107P/Wilson–Harrington), 60558 Echeclus (174P/Echeclus), 118401 LINEAR (176P/LINEAR), {{mpl|323137|2003 BM|80}} (282P/2003 BM₈₀), {{mpl|300163|2006 VW|139}} (288P/2006 VW₁₃₉), {{mpl|457175|2008 GO|98}} (362P/2008 GO₉₈), and {{mpl|248370|2005 QN|173}} (433P/2005 QN₁₇₃).[https://minorplanetcenter.net/iau/ECS/MPCArchive/2021/MPC_20210920.pdf M.P.C. 133823] As a dual status object, astrometric observations of 7968 Elst–Pizarro should be reported under the minor planet designation.

Exploration

Castalia is a proposed mission concept for a robotic spacecraft to explore 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.

Castalia mission scientists are now considering instrument contributions for the Chinese ZhengHe comet exploration mission, which will conduct detailed remote sensing and in-situ measurements at Elst–Pizarro in 2032{{cite web |last=Snodgrass |first=Colin |url=http://www.astro.sk/AFTERROSETTA/wp-content/uploads/2018/10/future-MBC-missions.pdf |title=Exploring the next frontier: the Main Belt Comets – Chinese MBC mission |work=University of Edinburgh |page=20 |date=October 2018 |access-date=20 June 2019}} following a proposed launch in 2025.{{cite web |last=Jones |first=Andrew |url=https://spacenews.com/china-outlines-space-plans-to-2025/ |title=China outlines space plans to 2025 |work=SpaceNews |date=30 June 2021 |access-date=30 June 2021}}

References

{{reflist

|refs=

{{cite web

|url=http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html

|title=Main-Belt Comets May Have Been Source Of Earths Water

|work=Space Daily

|date=23 March 2006}}

{{cite web

|url=https://minorplanetcenter.net/mpec/J96/J96R07.html

|title=MPEC 1996-R07 : COMET P/1996 N2 (ELST-PIZARRO)

|publisher=IAU-Minor Planet Center

|date=12 September 1996}}

{{cite web

|url=http://cbat.eps.harvard.edu/iauc/06400/06473.html#Item2

|title=IAUC 6473

|work=IAU-Central Bureau for Astronomical Telegrams

|date=12 September 1996}}

{{cite web

|url=http://cbat.eps.harvard.edu/iauc/06400/06457.html#Item1

|title=IAUC 6457

|work=IAU-Central Bureau for Astronomical Telegrams

|date=21 August 1996}}

{{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=August 10, 2009 }}

{{cite web

|title=Main Belt Comets

|publisher=UCLA, Department of Earth and Space Sciences

|author=David Jewitt

|author-link=David Jewitt

|url=http://www2.ess.ucla.edu/~jewitt/mbc.html

|access-date=2010-12-15}}

{{cite web

|type=2012-06-06 last obs

|title=JPL Small-Body Database Browser: 7968 Elst–Pizarro (1996 N2)

|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=133P

|access-date=13 April 2016

|url-status=dead

|archive-url=https://archive.today/20120809003324/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=133P

|archive-date=9 August 2012

}} from the original on 2012-08-08

{{cite journal

|last=Hsieh |first=Henry H.

|author2=Jewitt, David C.

|author3=Fernández, Yanga R.

|title=Albedos of Main-Belt Comets 133P/Elst–Pizarro and 176P/LINEAR

|journal=The Astrophysical Journal Letters

|volume=694 |issue=2 |pages=L111–L114 |date=2009

|doi=10.1088/0004-637X/694/2/L111

|arxiv=0902.3682

|bibcode=2009ApJ...694L.111H|s2cid=17438376

}}

{{cite journal

|last=Hsieh |first=Henry H.

|author2=Jewitt, David C.

|author3=Fernández, Yanga R.

|title=The Strange Case of 133P/Elst–Pizzarro: A Comet Among the Asteroids

|journal=The Astronomical Journal

|volume=127 |issue=5 |pages=2997–3017

|date=2004

|doi=10.1086/383208

|bibcode=2004AJ....127.2997H|citeseerx=10.1.1.362.9950|s2cid=14087115

}}

{{cite journal

|last=Hsieh |first=Henry H.

|author2=Jewitt, David C.

|author3=Lacerda, Pedro

|author4=Lowry, Stephen C.

|author5=Snodgrass, Colin

|title=The return of activity in main-belt comet 133P/Elst–Pizarro

|journal=Monthly Notices of the Royal Astronomical Society

|volume=403 |issue=1 |pages=363–377

|date=2010

|doi=10.1111/j.1365-2966.2009.16120.x

|doi-access=free

|arxiv=0911.5522

|bibcode=2010MNRAS.403..363H|s2cid=118438991

}}

{{cite journal|arxiv=1912.06266|author1=Liang Liang Yu|title=Low-activity Main-belt Comet 133P/Elst-Pizarro: New Constraints on Its Albedo, Temperature, and Active Mechanism from a Thermophysical Perspective|last2=Hsia|first2=Chih-Hao|author-link3=Ip Wing-huen|last3=Ip|first3=Wing-Huen|journal=The Astronomical Journal|year=2020|volume=159|issue=2|page=66|doi=10.3847/1538-3881/ab61f7|bibcode=2020AJ....159...66Y|s2cid=209370820 |doi-access=free }}

{{cite web

|date=2008-03-06

|title= Dual-Status Objects

|publisher=Minor Planet Center

|url=http://www.minorplanetcenter.org/iau/lists/DualStatus.html

|access-date=2018-02-13}}

}}