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6478 Gault

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6478 Gault
Gault's two comet-like tails seen fromHubbleon February 5th 2019[1]
Discovery [2]
Discovered byC. Shoemaker
E. Shoemaker
Discovery sitePalomar Obs.
Discovery date12 May 1988
Designations
(6478) Gault
Pronunciation/ˈɡɔːlt/
Named after
Donald Gault [2]
(American planetary geologist)
1988 JC1·1995 KC1
main-belt [2][3]·(inner)
Phocaea [4][5]·MBC
Orbital characteristics [3]
Epoch17 December 2020 (JD2459200.5)
Uncertainty parameter0
Observation arc62.10yr(22,681 d)
Earliestprecoverydate11 December 1958
Aphelion2.7513AU
Perihelion1.8587 AU
2.3050 AU
Eccentricity0.1936
3.50 yr (1,278 d)
98.412°
0° 16m53.76s/ day
Inclination22.813°
183.538°
2023-Jul-04[6]
83.172°
Physical characteristics
2.8+0.4
−0.2km[7]
2.4929±0.0003h[7]
0.26±0.05[7]
0.13±0.04[8]
S (est.family-based)
14.4[2][3]

6478 Gault,provisional designation1988 JC1,is aPhocaea asteroidfrom the inner regions of theasteroid belt,approximately 3.7 kilometers (2.3 miles) in diameter. The likelyS-type asteroidwas discovered on 12 May 1988, by astronomer coupleCarolynandEugene Shoemakerat thePalomar Observatoryin California. It was named in honor of planetary geologistDonald Gault.[2]In January 2019, it was found thatGaultshowscometary activityand that it has multipletails,making it anactive asteroid.[9]It was subsequently realised that it had been active since at least 2013.[10]

Orbit and classification

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Gaultis a core member of thePhocaea family(701).[4][5]The largeasteroid familyconsists of nearly 2,000 known stony asteroids, and was named after its largest member,25 Phocaea.The old family formed up to 2.2 billion years ago and has the highest inclination of all families in theinnerasteroid belt. Several of its members are alsoMars-crossing asteroidswith high eccentricities.[11][12]: 23 

It orbits the Sun at a distance of 1.9–2.8AUonce every 3 years and 6 months (1,278 days;semi-major axisof 2.31 AU). Its orbit has aneccentricityof 0.19 and aninclinationof 23°with respect to theecliptic.[3]The body'sobservation arcbegins with its official discovery observation atPalomarin May 1988.[2]It last came toperihelionin January 2020 and will next come to perihelion in July 2023.[6]

Main-belt comet

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On January 5, 2019, it was discovered thatGaultpossesses acomet tail,which had not been present in previous images taken during the 2018/19 opposition.[13][9]The asteroid began to break up as its spin accelerated due to theYORP effect,and its rotation speed approached two hours – near the limit of stability for an asteroid. The ejected matter created two dust tails,[14]and the longer one has been estimated at over 800,000 km (500,000 mi) long. Earlier hypotheses of a collision with another asteroid were ruled out as a source of the tail-forming dust, and its two tails were believed to be a result of sudden dust ejections near October 28 and December 30, 2018.[9]It is also possible that solar heating caused sublimation of ice, perhaps beneath the surface in a "pocket," and the force of the ejection of material (after being exposed to solar heating during the rotation of the asteroid) resulted in the spin rate increase. A prior example of such an occurrence is in the literature.[15]

In April 2019, upon analyzing archive images taken in 2013, 2016 and 2017, it was found thatGaulthad been perpetually active for at least five years before the discovery, with a tail visible when the asteroid was near its furthest distance from the Sun during the 2013 apparition. If its activity is indeed caused by a rotational breakup, thenGaulthas remained active far longer than any other object of this type seen before. This indicates that it may represent a new type of object.[10]

Naming

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Thisminor planetwas named in memory of American planetary geologistDonald Gault(1923–1999), an expert in the field ofimpact craterforming processes. Gault conducted field experiments and applied his insight to the interpretation of impact data from the Moon, Earth, Mars and Mercury.[2]The officialnaming citationwas published by theMinor Planet Centeron 28 July 1999 (M.P.C.35484).[16]

Physical characteristics

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Gault'sspectral typeresembles that of a stonyS-type asteroid,according its membership to thePhocaea family,[4]but some of the features of the spectrum are more similar to the carbonaceousC-type asteroidclass.[14]Based on a generic magnitude-to-diameter conversion,[17]the asteroid measures approximately 3.7 kilometers in diameter, for an assumed family-specific albedo of 0.22,[12]: 23 and anabsolute magnitudeof 14.4.[2]RotationallightcurvesofGaultobtained fromphotometricobservations in 2019 showed a rotation period of either 1.79 or 3.36 hours.[14][3]The body'spoleand shape remain unknown,[3][18]but based on its lightcurve, its surface likely has irregularities and concavities.[8]

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  • Background stars surrounding asteroid 6478 Gault and its tails.[19]
    Background stars surrounding asteroid 6478 Gault and its tails.[19]
  • (6478) Gault imaged on 2019-03-26 with iTelescope's T21
    (6478) Gault imaged on 2019-03-26 withiTelescope'sT21
  • JPL Small-Body Database Browser's Orbit Diagram for the Main-belt Asteroid 6478 Gault on 2019-01-01 at 00:00 UTC
    JPL Small-Body Database Browser's Orbit Diagram for the Main-belt Asteroid 6478 Gault on 2019-01-01 at 00:00 UTC

References

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  1. ^"What Did Hubble See on Your Birthday?".28 February 2020.
  2. ^abcdefgh"6478 Gault (1988 JC1)".Minor Planet Center.Retrieved10 January2019.
  3. ^abcdef"JPL Small-Body Database Browser: 6478 Gault (1988 JC1)"(2017-11-28 last obs.).Jet Propulsion Laboratory.Retrieved10 January2019.
  4. ^abc"Asteroid 6478 Gault".Small Bodies Data Ferret.Retrieved10 January2019.
  5. ^ab"Asteroid (6478) Gault – Proper elements".AstDyS-2, Asteroids – Dynamic Site.Retrieved25 May2018.
  6. ^abJPL HorizonsObserver Location: @sun (Perihelion occurs when deldot changes from negative to positive.)
  7. ^abcDevogèle, Maxime; Ferrais, Marin; Jehin, Emmanuel; Moskovitz, Nicholas; Skiff, Brian A.; Levine, Stephen E.; Gustafsson, Annika; Farnocchia, Davide; Micheli, Marco; Snodgrass, Colin; Borisov, Galin; Manfroid, Jean; Moulane, Youssef; Benkhaldoun, Zouhair; Burdanov, Artem; Pozuelos, Francisco J.; Gillon, Michael; De Wit, Julien; Green, Simon F.; Bendjoya, Philippe; Rivet, Jean-Pierre; Abe, Luy; Vernet, David; Chandler, Colin Orion; Trujillo, Chadwick A. (2021), "(6478) Gault: Physical characterization of an active main-belt asteroid",Monthly Notices of the Royal Astronomical Society,505:245–258,arXiv:2104.11177,doi:10.1093/mnras/stab1252
  8. ^abCarbognani, Albino; Buzzoni, Alberto; Stirpe, Giovanna (2021)."Physical characterization of the active asteroid (6478) Gault".Monthly Notices of the Royal Astronomical Society.506(4): 5774–5780.arXiv:2107.08956.Bibcode:2021MNRAS.506.5774C.doi:10.1093/mnras/stab2111.
  9. ^abcGarner, Rob (28 March 2019)."Hubble Watches Spun-Up Asteroid Coming Apart".NASA.Retrieved28 March2019.
  10. ^abC. O. Chandler; J. Kueny; A. Gustafsson; C. A. Trujillo; T. D. Robinson; D. E. Trilling (23 April 2019),Six Years of Sustained Activity from Active Asteroid (6478) Gault,arXiv:1904.10530
  11. ^Carruba, V. (September 2009)."An analysis of the region of the Phocaea dynamical family".Monthly Notices of the Royal Astronomical Society.398(3): 1512–1526.Bibcode:2009MNRAS.398.1512C.doi:10.1111/j.1365-2966.2009.15220.x.hdl:11449/9436.
  12. ^abNesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families".Asteroids IV.pp. 297–321.arXiv:1502.01628.Bibcode:2015aste.book..297N.doi:10.2458/azu_uapress_9780816532131-ch016.ISBN9780816532131.S2CID119280014.
  13. ^Recent CBETs (CBET 4594),Minor Planet Electronic Circular,IAU–Minor Planet Center
  14. ^abcIvanova, Oleksandra; Skorov, Yuri; Luk'yanyk, Igor; Tomko, Dušan; Husárik, Marek; Blum, Jürgen; Egorov, Oleg; Voziakova, Olga (2020)."Activity of (6478) Gault during 2019 January 13–March 28".Monthly Notices of the Royal Astronomical Society.496(3): 2636–2647.arXiv:2005.12030.doi:10.1093/mnras/staa1630.
  15. ^Russell, Ray (1986). "Multiple aperture airborne infrared measurements of Comet Halley".ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 2: Dust and Nucleus (SEE N87-25908 19-90).Vol. 250. pp. 125–128.Bibcode:1986ESASP.250b.125R.
  16. ^"MPC/MPO/MPS Archive".Minor Planet Center.Retrieved10 January2019.
  17. ^"Asteroid Size Estimator".CNEOS NASA/JPL.Retrieved10 January2019.
  18. ^"LCDB Data for (6478) Gault – Not in Data Base".Asteroid Lightcurve Database (LCDB).Retrieved10 January2019.
  19. ^"Hubble Captures Rare Active Asteroid".spacetelescope.org.Retrieved29 March2019.
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