7968 Elst–Pizarro Explained

Minorplanet:yes
Background:
  1. D6D6D6
7968 Elst–Pizarro
133P/Elst–Pizarro
Discoverer:


M. R. S. Hawkins

Discovered:24 July 1979  
14 July 1996 (1996 N2)
Mpc Name:(7968) Elst–Pizarro
Alt Names:P/1996 N2
Mp Category:Main-belt comet
Main-belt asteroid
Themis/ Beagle family
Epoch:13 January 2016 (JD 2457400.5)
Semimajor:3.16AU (a)
Perihelion:2.6524AU (q)
Time Periastron:2024-May-10[1]
Aphelion:3.66751abbr=onNaNabbr=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)
Dimensions:
 km
Rotation:3.471abbr=onNaNabbr=on
Magnitude:17.24 to 20.71
Abs Magnitude:15.7
15.3R (2004)
15.49R (2010)
Albedo:0.074±0.013R
Mean Motion: / day (n)
Observation Arc:13350 days (36.55 yr)
Uncertainty:0
Jupiter Moid:1.51427AU
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.

Elst–Pizarro was reported in 1979 as minor planet,[2] 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.[3]

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 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), (282P/2003 BM80), (288P/2006 VW139), (362P/2008 GO98), and (433P/2005 QN173).[4] 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.[5] 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.[5] Because of the construction time required and orbital dynamics, a launch date of October 2028 was proposed.[5]

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[6] following a proposed launch in 2025.[7]

Notes and References

  1. Web site: Horizons Batch for 7968 Elst-Pizarro (1996 N2) on 2024-May-10 . . Perihelion occurs when rdot flips from negative to positive . 2023-04-29. (JPL#70/Soln.date: 2023-Apr-25
  2. Web site: Hsieh . Henry . Active Asteroids . Oxford Research Encyclopedias . 2020 . Oxford University Press . 3 October 2023 . 10.1093/acrefore/9780190647926.013.188 . 978-0-19-064792-6 .
  3. Web site: Strange Comet Discovered at ESO . ESO . 16 September 1996.
  4. https://minorplanetcenter.net/iau/ECS/MPCArchive/2021/MPC_20210920.pdf M.P.C. 133823
  5. 10.1016/j.asr.2017.09.011. The Castalia mission to Main Belt Comet 133P/Elst-Pizarro. Advances in Space Research. 62. 8. 1947–1976. 2018. Snodgrass. C.. Jones. G.H.. Boehnhardt. H.. Gibbings. A.. Homeister. M.. Andre. N.. Beck. P.. Bentley. M.S.. Bertini. I.. Bowles. N.. Capria. M.T.. Carr. C.. Ceriotti. M.. Coates. A.J.. Della Corte. V.. Donaldson Hanna. K.L.. Fitzsimmons. A.. Gutiérrez. P.J.. Hainaut. O.R.. Herique. A.. Hilchenbach. M.. Hsieh. H.H.. Jehin. E.. Karatekin. O.. Kofman. W.. Lara. L.M.. Laudan. K.. Licandro. J.. Lowry. S.C.. Marzari. F.. 29. 2018AdSpR..62.1947S. 1709.03405. 55821241.
  6. Web site: Snodgrass . Colin . Exploring the next frontier: the Main Belt Comets – Chinese MBC mission . . 20 . October 2018 . 20 June 2019.
  7. Web site: Jones . Andrew . China outlines space plans to 2025 . . 30 June 2021 . 30 June 2021.