_Gault_(2019-22-4379).png) | |
| Discovery[2] | |
|---|---|
| Discovered by | C. Shoemaker E. Shoemaker |
| Discovery site | Palomar Obs. |
| Discovery date | 12 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] | |
| Epoch 17 December 2020 (JD 2459200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 62.10yr (22,681 d) |
| Earliestprecovery date | 3 September 1957[6]: 5 |
| Aphelion | 2.7513AU |
| Perihelion | 1.8587 AU |
| 2.3050 AU | |
| Eccentricity | 0.1936 |
| 3.50 yr (1,278 d) | |
| 98.412° | |
| 0° 16m 53.76s / day | |
| Inclination | 22.813° |
| 183.538° | |
| 2023-Jul-04[7] | |
| 83.172° | |
| Physical characteristics | |
| 2.8+0.4 −0.2 km[6] | |
| 2.4929±0.0003h[6] | |
| 0.26±0.05[6] 0.13±0.04[8] | |
| S(est.family-based) | |
| 14.4[2][3] | |
6478 Gault (provisional designation1988 JC1) is aPhocaea asteroid from the inner regions of theasteroid belt, approximately 3.7 kilometers (2.3 miles) in diameter. The likelyS-type asteroid was discovered on 12 May 1988 by astronomer coupleCarolyn andEugene Shoemaker at thePalomar Observatory in California. It was named in honor of planetary geologistDonald Gault.[2] In January 2019, it was found that Gault showscometary activity and that it has multipletails, making it anactive asteroid.[9] It was subsequently realised that it had been active since at least 2013.[10]
Gault is a core member of thePhocaea family (701).[4][5] The largeasteroid family consists 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 theinner asteroid belt. Several of its members are alsoMars-crossing asteroids with high eccentricities.[11][12]: 23
It orbits the Sun at a distance of 1.9–2.8 astronomical units (AU) once every 3 years and 6 months (1,278 days;semi-major axis of 2.31 AU). Its orbit has aneccentricity of 0.19 and aninclination of 23° with respect to theecliptic.[3] The body'sobservation arc begins with its official discovery observation atPalomar in May 1988.[2] It last came toperihelion in July 2023 and will next come to perihelion in January 2027.[7]
Thisminor planet was named in memory of American planetary geologistDonald Gault (1923–1999), an expert in the field ofimpact crater forming 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 citation was published by theMinor Planet Center on 28 July 1999 (M.P.C. 35484).[13]
Gault'sspectral type resembles 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 asteroid class.[14] Based on a generic magnitude-to-diameter conversion,[15] the asteroid measures approximately 3.7 kilometers in diameter, for an assumed family-specific albedo of 0.22,[12]: 23 and anabsolute magnitude of 14.4.[2] Rotationallightcurves ofGault obtained fromphotometric observations in 2019 showed a rotation period of either 1.79 or 3.36 hours.[14][3] The body'spole and shape remain unknown,[3][16] but based on its lightcurve, its surface likely has irregularities and concavities.[8]
On January 5, 2019, it was discovered that Gault possesses acomet tail, which had not been present in previous images taken during the 2018/19 opposition.[17][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.[18]
In April 2019, upon analyzing archive images taken in 2013, 2016 and 2017, it was found that Gault had 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, then Gault has 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]
Between late 2018 and early 2019, the asteroid underwent multiple outbursts with tails morphologically similar to the ejecta fromDimorphos following theDouble Asteroid Redirection Test (DART) mission.[19] The first outbursts occurred on the 18 October, and the second outbursts occurred on the 24 December. They released a mass of2×107 kg and1×106 kg, respectively. The ejected dust grains consist of particles up to 10 μm in size and have velocities below a meter per second regardless of particle size. Previous observations of Gault shown no record of activity.[20]
![Background stars surrounding asteroid 6478 Gault and its tails.[21]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aHeic1906a_Asteroid_6478_Gault.jpg)
_Gault_on_2019-03-26.jpg)
