Rings of Jupiter
The planet
The Jovian ring system is faint and consists mainly of dust.[1][5] It has four main components: a thick inner torus of particles known as the "halo ring"; a relatively bright, exceptionally thin "main ring"; and two wide, thick and faint outer "gossamer rings", named for the moons of whose material they are composed: Amalthea and Thebe.[6]
The main and halo rings consist of dust ejected from the moons Metis, Adrastea and perhaps smaller, unobserved bodies as the result of high-velocity impacts.[2] High-resolution images obtained in February and March 2007 by the New Horizons spacecraft revealed a rich fine structure in the main ring.[7]
In visible and near-infrared light, the rings have a reddish color, except the halo ring, which is neutral or blue in color.[3] The size of the dust in the rings varies, but the cross-sectional area is greatest for nonspherical particles of radius about 15 μm in all rings except the halo.[8] The halo ring is probably dominated by submicrometre dust. The total mass of the ring system (including unresolved parent bodies) is poorly constrained, but is probably in the range of 1011 to 1016 kg.[9] The age of the ring system is also not known, but it is possible that it has existed since the formation of Jupiter.[9]
A ring or ring arc appears to exist close to the moon Himalia's orbit. One explanation is that a small moon recently crashed into Himalia and the force of the impact ejected the material that forms the ring.
Discovery and structure
Jupiter's ring system was the third to be discovered in the
In 2022, dynamical simulations suggested that the reltive meagreness of Jupiter's ring system, compared to that of the smaller Saturn, is due to destabilising resonances created by the
Name | Radius (km) | Width (km) | Thickness (km) | Optical depth[a] (in τ) | Dust fraction | Mass, kg | Notes |
---|---|---|---|---|---|---|---|
Halo ring | 92,000–122,500 | 30,500 | 12,500 | ~1 × 10−6 | 100% | — | |
Main ring | 122,500–129,000 | 6,500 | 30–300 | 5.9 × 10−6 | ~25% | 107– 109 (dust) 1011– 1016 (large particles) |
Bounded by Adrastea |
Amalthea gossamer ring | 129,000–182,000 | 53,000 | 2,000 | ~1 × 10−7 | 100% | 107– 109 | Connected with Amalthea |
Thebe gossamer ring | 129,000–226,000 | 97,000 | 8,400 | ~3 × 10−8 | 100% | 107– 109 | Connected with Thebe. There is an extension beyond the orbit of Thebe. |
Main ring
Appearance and structure
The narrow and relatively thin main ring is the brightest part of Jupiter's ring system. Its outer edge is located at a radius of about 129,000 km (1.806 RJ;RJ = equatorial radius of Jupiter or 71,398 km) and coincides with the orbit of Jupiter's smallest inner satellite, Adrastea.[2][5] Its inner edge is not marked by any satellite and is located at about 122,500 km (1.72 RJ).[2]
Thus the width of the main ring is around 6,500 km. The appearance of the main ring depends on the viewing geometry.[9] In forward-scattered light[b] the brightness of the main ring begins to decrease steeply at 128,600 km (just inward of the Adrastean orbit) and reaches the background level at 129,300 km—just outward of the Adrastean orbit.[2] Therefore, Adrastea at 129,000 km clearly shepherds the ring.[2][5] The brightness continues to increase in the direction of Jupiter and has a maximum near the ring's center at 126,000 km, although there is a pronounced gap (notch) near the Metidian orbit at 128,000 km.[2] The inner boundary of the main ring, in contrast, appears to fade off slowly from 124,000 to 120,000 km, merging into the halo ring.[2][5] In forward-scattered light all Jovian rings are especially bright.
In back-scattered light
Observed in back-scattered light the main ring appears to be razor thin, extending in the vertical direction no more than 30 km.[5] In the side scatter geometry the ring thickness is 80–160 km, increasing somewhat in the direction of Jupiter.[2][8] The ring appears to be much thicker in the forward-scattered light—about 300 km.[2] One of the discoveries of the Galileo orbiter was the bloom of the main ring—a faint, relatively thick (about 600 km) cloud of material which surrounds its inner part.[2] The bloom grows in thickness towards the inner boundary of the main ring, where it transitions into the halo.[2]
Detailed analysis of the Galileo images revealed longitudinal variations of the main ring's brightness unconnected with the viewing geometry. The Galileo images also showed some patchiness in the ring on the scales 500–1000 km.[2][9]
In February–March 2007
Spectra and particle size distribution
The properties of the main ring can be explained by the hypothesis that it contains significant amounts of dust with 0.1–10 μm particle sizes. This explains the stronger forward-scattering of light as compared to back-scattering.[9][12] However, larger bodies are required to explain the strong back-scattering and fine structure in the bright outer part of the main ring.[9][12]
Analysis of available phase and spectral data leads to a conclusion that the size distribution of small particles in the main ring obeys a power law[8][18][19]
where n(r) dr is a number of particles with radii between r and r + dr and is a normalizing parameter chosen to match the known total light flux from the ring. The parameter q is 2.0 ± 0.2 for particles with r < 15 ± 0.3 μm and q = 5 ± 1 for those with r > 15 ± 0.3 μm.[8] The distribution of large bodies in the mm–km size range is undetermined presently.[9] The light scattering in this model is dominated by particles with r around 15 μm.[8][17]
The power law mentioned above allows estimation of the optical depth[a] of the main ring: for the large bodies and for the dust.[8] This optical depth means that the total cross section of all particles inside the ring is about 5000 km².[d][9] The particles in the main ring are expected to have aspherical shapes.[8] The total mass of the dust is estimated to be 107−109 kg.[9] The mass of large bodies, excluding Metis and Adrastea, is 1011−1016 kg. It depends on their maximum size— the upper value corresponds to about 1 km maximum diameter.[9] These masses can be compared with masses of Adrastea, which is about 2 × 1015 kg,[9] Amalthea, about 2 × 1018 kg,[20] and Earth's Moon, 7.4 × 1022 kg.
The presence of two populations of particles in the main ring explains why its appearance depends on the viewing geometry.[19] The dust scatters light preferably in the forward direction and forms a relatively thick homogenous ring bounded by the orbit of Adrastea.[9] In contrast, large particles, which scatter in the back direction, are confined in a number of ringlets between the Metidian and Adrastean orbits.[9][12]
Origin and age
The dust is constantly being removed from the main ring by a combination of
Vertical corrugations
Images from the Galileo and New Horizons space probes show the presence of two sets of spiraling vertical corrugations in the main ring. These waves became more tightly wound over time at the rate expected for differential nodal regression in Jupiter's gravity field. Extrapolating backwards, the more prominent of the two sets of waves appears to have been excited in 1995, around the time of the impact of
Halo ring
Appearance and structure
The halo ring is the innermost and the vertically thickest Jovian ring. Its outer edge coincides with the inner boundary of the main ring approximately at the radius 122500 km (1.72 RJ).[2][5] From this radius the ring becomes rapidly thicker towards Jupiter. The true vertical extent of the halo is not known but the presence of its material was detected as high as 10000 km over the ring plane.[2][4] The inner boundary of the halo is relatively sharp and located at the radius 100000 km (1.4 RJ),[4] but some material is present further inward to approximately 92000 km.[2] Thus the width of the halo ring is about 30000 km. Its shape resembles a thick torus without clear internal structure.[9] In contrast to the main ring, the halo's appearance depends only slightly on the viewing geometry.
The halo ring appears brightest in forward-scattered light, in which it was extensively imaged by Galileo.[2] While its surface brightness is much less than that of the main ring, its vertically (perpendicular to the ring plane) integrated photon flux is comparable due to its much larger thickness. Despite a claimed vertical extent of more than 20000 km, the halo's brightness is strongly concentrated towards the ring plane and follows a power law of the form z−0.6 to z−1.5,[9] where z is altitude over the ring plane. The halo's appearance in the back-scattered light, as observed by Keck[4] and HST,[3] is the same. However its total photon flux is several times lower than that of the main ring and is more strongly concentrated near the ring plane than in the forward-scattered light.[9]
The spectral properties of the halo ring are different from the main ring. The flux distribution in the range 0.5–2.5 μm is flatter than in the main ring;[3] the halo is not red and may even be blue.[16]
Origin of the halo ring
The optical properties of the halo ring can be explained by the hypothesis that it comprises only dust with particle sizes less than 15 μm.[3][9][18] Parts of the halo located far from the ring plane may consist of submicrometre dust.[3][4][9] This dusty composition explains the much stronger forward-scattering, bluer colors and lack of visible structure in the halo. The dust probably originates in the main ring, a claim supported by the fact that the halo's optical depth is comparable with that of the dust in the main ring.
Gossamer rings
Amalthea gossamer ring
The Amalthea gossamer ring is a very faint structure with a rectangular cross section, stretching from the orbit of Amalthea at 182000 km (2.54 RJ) to about 129000 km (1.80 RJ).[2][9] Its inner boundary is not clearly defined because of the presence of the much brighter main ring and halo.[2] The thickness of the ring is approximately 2300 km near the orbit of Amalthea and slightly decreases in the direction of Jupiter.[f][4] The Amalthea gossamer ring is actually the brightest near its top and bottom edges and becomes gradually brighter towards Jupiter; one of the edges is often brighter than another.[29] The outer boundary of the ring is relatively steep;[2] the ring's brightness drops abruptly just inward of the orbit of Amalthea,[2] although it may have a small extension beyond the orbit of the satellite ending near 4:3 resonance with Thebe.[14] In forward-scattered light the ring appears to be about 30 times fainter than the main ring.[2] In back-scattered light it has been detected only by the Keck telescope[4] and the ACS (Advanced Camera for Surveys) on HST.[12] Back-scattering images show additional structure in the ring: a peak in the brightness just inside the Amalthean orbit and confined to the top or bottom edge of the ring.[4][14]
In 2002–2003 Galileo spacecraft had two passes through the gossamer rings. During them its dust counter detected dust particles in the size range 0.2–5 μm.[30][31] In addition, the Galileo spacecraft's star scanner detected small, discrete bodies (< 1 km) near Amalthea.[32] These may represent collisional debris generated from impacts with this satellite.
The detection of the Amalthea gossamer ring from the ground, in Galileo images and the direct dust measurements have allowed the determination of the particle size distribution, which appears to follow the same power law as the dust in the main ring with q=2 ± 0.5.[12][31] The optical depth of this ring is about 10−7, which is an order of magnitude lower than that of the main ring, but the total mass of the dust (107–109 kg) is comparable.[6][21][31]
Thebe gossamer ring
The Thebe gossamer ring is the faintest Jovian ring. It appears as a very faint structure with a rectangular cross section, stretching from the Thebean orbit at 226000 km (3.11 RJ) to about 129000 km (1.80 RJ;).[2][9] Its inner boundary is not clearly defined because of the presence of the much brighter main ring and halo.[2] The thickness of the ring is approximately 8400 km near the orbit of Thebe and slightly decreases in the direction of the planet.[f][4] The Thebe gossamer ring is brightest near its top and bottom edges and gradually becomes brighter towards Jupiter—much like the Amalthea ring.[29] The outer boundary of the ring is not especially steep, stretching over 15000 km.[2] There is a barely visible continuation of the ring beyond the orbit of Thebe, extending up to 280000 km (3.75 RJ) and called the Thebe Extension.[2][31] In forward-scattered light the ring appears to be about 3 times fainter than the Amalthea gossamer ring.[2] In back-scattered light it has been detected only by the Keck telescope.[4] Back-scattering images show a peak of brightness just inside the orbit of Thebe.[4] In 2002–2003 the dust counter of the Galileo spacecraft detected dust particles in the size range 0.2–5 μm—similar to those in the Amalthea ring—and confirmed the results obtained from imaging.[30][31]
The optical depth of the Thebe gossamer ring is about 3 × 10−8, which is three times lower than the Amalthea gossamer ring, but the total mass of the dust is the same—about 107–109 kg.[6][21][31] However the particle size distribution of the dust is somewhat shallower than in the Amalthea ring. It follows a power law with q < 2. In the Thebe extension the parameter q may be even smaller.[31]
Origin of the gossamer rings
The dust in the gossamer rings originates in essentially the same way as that in the main ring and halo.
However some properties have so far gone unexplained, like the Thebe Extension, which may be due to unseen bodies outside Thebe's orbit, and structures visible in the back-scattered light.[9] One possible explanation of the Thebe Extension is influence of the electromagnetic forces from the Jovian magnetosphere. When the dust enters the shadow behind Jupiter, it loses its electrical charge fairly quickly. Since the small dust particles partially corotate with the planet, they will move outward during the shadow pass creating an outward extension of the Thebe gossamer ring.[33] The same forces can explain a dip in the particle distribution and ring's brightness, which occurs between the orbits of Amalthea and Thebe.[31][33]
The peak in the brightness just inside of the Amalthea's orbit and, therefore, the vertical asymmetry the Amalthea gossamer ring may be due to the dust particles trapped at the leading (L4) and trailing (L5)
Himalia ring
In September 2006, as NASA's New Horizons mission to Pluto approached Jupiter for a gravity assist, it photographed what appeared to be a faint, previously unknown planetary ring or ring arc, parallel with and slightly inside the orbit of the irregular satellite Himalia. The amount of material in the part of the ring or arc imaged by New Horizons was at least 0.04 km3, assuming it had the same albedo as Himalia. If the ring (arc) is debris from Himalia, it must have formed quite recently, given the century-scale precession of the Himalian orbit. It is possible that the ring could be debris from the impact of a very small undiscovered moon into Himalia, suggesting that Jupiter might continue to gain and lose small moons through collisions.[34]
Exploration
The existence of the Jovian rings was inferred from observations of the planetary
Gallery
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The ring system as imaged by Galileo
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The rings as observed from the inside by Juno
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James Webb Space Telescope's photo of Jupiter and rings in infrared at 2.12 and 3.23 μm
See also
Notes
- ^ a b The normal optical depth is the ratio between the total cross section of the ring's particles to the square area of the ring.[8]
- ^ The forward-scattered light is the light scattered at a small angle relative to solar light.
- ^ The back-scattered light is the light scattered at an angle close to 180° relative to solar light.
- ^ ^ It should be compared with approximately 1700 km² total cross section of Metis and Adrastea.[9]
- ^ Lorentz resonance is a resonance between particle's orbital motion and rotation of planetary magnetosphere, when the ratio of their periods is a rational number.[27]
- ^ a b The thickness of the gossamer rings is defined here as the distance between peaks of brightness at their top and bottom edges.[29]
References
- ^ S2CID 33147728.
- ^ .
- ^ .
- ^ .
- ^ .
- ^ S2CID 250909885. Archived from the originalon 2020-06-16. Retrieved 2007-06-17.
- ^ a b Morring, F. (May 7, 2007). "Ring Leader". Aviation Week & Space Technology: 80–83.
- ^ .
- ^ Bibcode:2004jpsm.book..241B.
- ISBN 978-1-4020-4520-2. Retrieved 5 March 2023.
- S2CID 250526615.
- ^ Bibcode:2005LPICo1280..130S. LPI Contribution No. 1280.
- ^ a b "Jupiter's Rings: Sharpest View". NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute. May 1, 2007. Archived from the original on November 13, 2014. Retrieved 2011-09-29.
- ^ .
- ^ S2CID 12995172. Archived from the original(PDF) on 2019-03-03.
- ^ .
- ^ S2CID 53941924. Archived from the original(PDF) on 2020-04-12.
- ^ .
- ^ a b c d e f Burns, J.A.; Hamilton, D.P.; Showalter, M.R. (2001). "Dusty Rings and Circumplanetary Dust: Observations and Simple Physics" (PDF). In Grun, E.; Gustafson, B. A. S.; Dermott, S. T.; Fechtig H. (eds.). Interplanetary Dust. Berlin: Springer. pp. 641–725.
- S2CID 924257.
- ^ PMID 10325220.
- ^ Mason, J.; Cook, J.-R. C. (2011-03-31). "Forensic sleuthing ties ring ripples to impacts". CICLOPS press release. Cassini Imaging Central Laboratory for Operations. Retrieved 2011-04-04.
- ^ "Subtle Ripples in Jupiter's Ring". PIA 13893 caption. NASA / Jet Propulsion Laboratory-Caltech / SETI. 2011-03-31. Retrieved 2011-04-04.
- ^ a b c
Showalter, M. R.; Hedman, M. M.; Burns, J. A. (2011). "The impact of comet Shoemaker-Levy 9 sends ripples through the rings of Jupiter" (PDF). S2CID 27371440. Archived from the original(PDF) on 2020-02-12.
- ^ "Tilting Saturn's rings". PIA 12820 caption. NASA / Jet Propulsion Laboratory / Space Science Institute. 2011-03-31. Retrieved 2011-04-04.
- ^
Hedman, M. M.; Burns, J. A.; Evans, M. W.; Tiscareno, M. S.; Porco, C. C. (2011). "Saturn's curiously corrugated C Ring". S2CID 11449779.
- ^ .
- ^ S2CID 36269909.
- ^ .
- ^ Bibcode:2004cosp...35.1582K.
- ^ S2CID 1154579.
- .
- ^ S2CID 205212936.
- Bibcode:2010LPI....41.2549C.
- S2CID 32239999.
- .
- ^ "Juno—NASA New Frontiers Mission to Jupiter". Retrieved 2007-06-06.
External links
- Jupiter Rings Fact Sheet
- Jupiter's Rings by NASA's Solar System Exploration
- NASA Pioneer project page
- NASA Voyager project page
- NASA Galileo project page
- NASA Cassini project space
- New Horizons project page
- Planetary Ring Node: Jupiter's Ring System
- Rings of Jupiter nomenclature from the USGS planetary nomenclature page