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The Formation of Jupiter's Faint Rings

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The Formation of Jupiter's Faint Rings R EPORTS sealing with coverslips, and this was subsequently filled with 100 mM sucrose solution. To begin generating The Formation of Jupiter’s vesicles from the film, we applied an alternating electric field to the electrodes (10 Hz, 10 V ) while the chamber was mounted and viewed on the stage of an inverted Faint Rings microscope. Giant vesicles attached to the film-coated electrode were visible after 15 to 60 min. These were 1 2 3 dissociated from the electrodes by lowering the fre- Joseph A. Burns, * Mark R. Showalter, Douglas P. Hamilton, 1 4 1 quency to 3 to 5 Hz for at least 15 min. The electro- Philip D. Nicholson, Imke de Pater, Maureen E. Ockert-Bell, formation method is adapted from that of M. I. Ange- 1 lova, S. Soleau, P. Meleard, J. F. Faucon, and P. Bothorel Peter C. Thomas [Prog. Coll. Polm. Sci. 89, 127 (1992)], as previously used by M. L. Longo, A. J. Waring, and D. A. Hammer Observations by the Galileo spacecraft and the Keck telescope showed that [Biophys. J. 73, 1430 (1997)]. The vesicles were stable Jupiter’s outermost (gossamer) ring is actually two rings circumscribed by the for at least several days when kept sealed from air in a gas-tight, plastic syringe. Of additional note, vesicles orbits of the small satellites Amalthea and Thebe. The gossamer rings’ unique were stable when resuspended in physiological saline at morphology—especially the rectangular end profiles at the satellite’s orbit and temperatures ranging from 10° to 50°C. Micromanipu- the enhanced intensities along the top and bottom edges of the rings—can be lation was done with micropipette systems analogous to those described by M. L. Longo et al. and D. E. Discher, explained by collisional ejecta lost from the inclined satellites. The ejecta N. Mohandas, and E. A. Evans [Science 266, 1032 evolves inward under Poynting-Robertson drag. This mechanism may also (1994)]. explain the origin of Jupiter’s main ring and suggests that faint rings may 11. E. Evans and W. Rawicz, Phys. Rev. Lett. 64, 2094 (1990); W. Helfrich and R.-M. Servuss, Nuovo Ci- accompany all small inner satellites of the other jovian planets. mento D3, 137 (1984). Note that Ka did not differ by more than 10 to 20% from its nonrenormalized The well-known, opaque rings of Saturn and and wider (Thebe) ring is terminated at the value. Uranus are populated primarily by centime- satellite Thebe’s orbit (221,900 km). Some 12. J. Israelachvili, Intermolecular and Surface Forces (Ac- ademic Press, New York, ed. 2, 1991). ter- to meter-sized particles. In addition, all very diffuse material, which we refer to as the 13. E. Evans and D. Needham, J. Phys. Chem. 91, 4219 four giant planets have extensive but much exterior gossamer material, seems to reach (1987). more tenuous rings (1, 2) containing mainly past Thebe, to perhaps 265,000 km. 14. I. Szleifer, D. Kramer, A. Ben-Shaul, D. Roux, W. M. Gelbart, Phys. Rev. Lett. 60, 1966 (1988); A. Ben- micrometer-sized particles. Because particle As seen in these almost edge-on images, Shaul, in (3), chap. 7. collisions are unimportant in such rarified Jupiter’s gossamer rings have a unique form. 15. A. G. Petrov and J. Bivas, Prog. Surf. Sci. 18, 359 systems and because small grains are sub- At their ansae, both rings have cross sections (1984). stantially perturbed by nongravitational forc- that are approximately rectangular, unlike the 16. R. R. Netz and M. Schick, Phys. Rev. E 53, 3875 (1996). In this reference, the self-consistent calcula- es, these ethereal rings provide valuable dy- elliptical ends typically noted in images of tion models lipids as nearly symmetric diblock copol- namical counterpoints to the dense, collision- thin, flat equatorial rings. As measured near ymers, which are clearly closer in form to the mole- ally dominated systems. the ansae, the half-thicknesses T of the gos- cules of this study. ; 5 17. D. Needham and R. S. Nunn, Biophys. J. 58, 997 Jupiter’s rings—the archetype of ethereal samer rings are 1300 km [inclination (i) (1990). ring systems—have three components (3): a 0.41°] for the Amalthea ring and ;4400 km 18. Because the average interfacial area per chain, ,A ., c main ring, an inner halo, and an outer gossa- (i 5 1.14°) for the Thebe ring, with uncer- in the lamellar state has been estimated to be ,A . c 6 6 * 2.5 nm2 per molecule, one estimates that E * 1.3 mer ring. The main ring of normal optical tainties of 100 km ( 0.03°). These values c t; 26 , kBT. depth 10 and thickness 30 km ex- are similar to the maximum excursions of the 19. Vesicles were prepared in 100 mOsm sucrose solu- tends radially inward about 6000 km (jovian satellites associated with these rings from tion, which established an initial, internal osmolarity. 5 They were then suspended in an open-edge chamber radius 71,398 km) from the orbit of the Jupiter’s equatorial plane [1160 and 4310 formed between cover slips and containing 100 tiny moon Adrastea, with a dip in brightness km, respectively, with errors of 6150 km mOsm glucose. A single vesicle was aspirated with a of 20 to 30% around Metis’s orbit (Table 1). (7)]. In addition, the radial excursions of the suction pressure sufficient to smooth membrane fluctuations; the pressure was then lowered to a Immediately interior to the main ring is the source satellites, as defined by their orbital 4 4 small holding pressure. With a second, transfer pi- halo, a ;10 -km-thick and ;2 3 10 -km- eccentricities, seem to determine the radial pette, the vesicle was moved to a second chamber wide torus of dust, with t comparable to the decrease in brightness at the ansae of both with 120 mOsm glucose. Water flows out of the main ring. Exterior to the main ring lies the rings (see crosses in Fig. 1A). vesicle due to the osmotic gradient between inside 27 and outside, which leads to an increased projection broad, fainter gossamer ring, with t;10 , The ring’s upper and lower edges are length that is monitored over time. The exponential whose inner portion was observed in one much brighter than their central cores (Fig. decrease in vesicle volume was calculated from video Voyager image (4). 1A), suggesting that the ring material is con- images and then fit to determine the permeability 5 6 The ring system’s structure was con- centrated near the edges. Furthermore, the coefficient (Pf)(4). For reference, Pf 23.5 1.7 mm/s for SOPC from this method. firmed and refined through images obtained height (off the equatorial plane) of the peak 20. H. J. Deuling and W. Helfrich, J. Phys. 37, 1335 by the Galileo spacecraft (5) and the Keck brightness in each gossamer ring decreases (1976); S. Svetina and B. Zeks, Eur. Biophys. 17, 101 (1989); U. Seifert, K. Berndl, R. Lipowsky, Phys. Rev. A 10-m telescope (6). The gossamer ring is linearly with projected radius as does the 44, 1182 (1991). actually two distinct, fairly uniform rings ring’s total vertical extent in backscattered 21. U. Seifert and R. Lipowsky, in (3), chap. 8; H.-G. (Fig. 1, A and B). The brighter and narrower light (6). A similar banded appearance was Dobreiner, E. Evans, M. Kraus, U. Seifert, M. Wortis, Phys. Rev. E 55, 4458 (1997). (Amalthea) ring is visible stretching radially inferred for the distribution of interplanetary 22. S. Chaieb and S. Rica, Phys. Rev. E 58, 7733 (1998). outward from the main ring to the satellite dust particles (IDPs) from Infrared Astro- 23. We thank E. A. Evans, D. Needham, P. Nelson, and T. Amalthea’s orbit at 181,350 km. The fainter nomical Satellite scans of the zodiacal light Lubensky for discussions. Support was primarily pro- vided by the NSF-supported Materials Research Sci- (8). The cause is likely the same: a swarm of ence and Engineering Center (MRSEC) at the Univer- 1Center for Radiophysics and Space Research, Cornell orbiting particles, with similar inclinations sity of Pennsylvania (DMR96-32598) and both the University, Ithaca, NY 14853, USA. 2Space, Telecom- but random node orientations, that spend Center for Interfacial Engineering (CIE) and the MR- munications and Radioscience Laboratory, Stanford more time at their vertical turning points SEC (DMR 98-09364) at the University of Minnesota. 3 University, Stanford, CA 94305, USA. Department of above and below the ecliptic (interplanetary The work was also supported in part by grants from Astronomy, University of Maryland, College Park, MD the Whitaker Foundation (D.D.) and National Insti- 20742, USA. 4Department of Astronomy, University case) or equatorial (jovian case) plane. tutes of Health [R01-HL62352-01(D.D.) and P01- of California, Berkeley, CA 94720, USA. In the Voyager discovery image (4) and in HLI8208 (D.H.)]. *To whom correspondence should be addressed. E- two early Galileo frames (5), the Amalthea ring 27 January 1999; accepted 5 April 1999 mail: [email protected] brightens by tens of percent with smaller scat- 1146 14 MAY 1999 VOL 284 SCIENCE www.sciencemag.org R EPORTS tering angles u, suggesting the photometric tical will escape the jovian ring moons from ter-sized grains are rapidly destroyed or dominance of micrometer-sized grains (9). To four equatorial surface locations (leading, Ju- swiftly removed from the system. Lifetimes estimate the phase brightening of Amalthea piter-facing, trailing, and anti-Jupiter) for ho- for 1-mm particles have been estimated as 102 ring particles, we removed a modeled Thebe mogeneous, rotationally locked satellites to 104 years for erosion by sputtering and 104 ring contribution and then derived the whose shapes have been measured (14).
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