The response of Jupiter's magnetosphere to an outburst on lo

Science

Volumn 278, Issue 5336, 1997, Pages 268-271

  Brown, Michael E ^a   Bouchez, Antonin H ^a  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; ATMOSPHERE; COSMOLOGICAL PHENOMENA; MAGNETIC FIELD; MOON; PRIORITY JOURNAL;

ATMOSPHERE; EXTRATERRESTRIAL ENVIRONMENT; JUPITER; OXYGEN; SODIUM; SULFUR;

EID: 0030771452     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.278.5336.268     Document Type: Article

References (34)

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2. See review by J. R. Spencer and N. M. Schneider [Annu. Rev. Earth Planet. Sci. 24, 125 (1996)].
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5. R. G. Strom and N. M. Schneider, in Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, 1982), pp. 598-533.
6. See review by N. M. Schneider, M. A. McGrath, and W. H. Smyth [in Time Variable Phenomena in the Jovian System, M. J. S. Belton et al., Eds. (NASA SP-494, 1989), pp. 75-99].
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9. See, for example, J. K. Wilson and N. M. Schneider, J. Geophys. Res., in press.
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13. + emission lines at 671.7 and 673.1 nm, or 589.0 nm, to record the extended neutral cloud Na lines at 588.9 and 589.6 nm. Details on the observations and the plasma torus data reduction can be found in M. Brown [thesis, University of California at Berkeley (1994)]. Reduction of the Na data followed essentially the same techniques, with additional complications due to the Na night-sky lines, the continuum spectrum of lo, and the water absorption features.
14. F. Bagenal, J. Geophys. Res. 99, 11043 (1994).
15. + density), as the emission is due to the electron impact excitation of the S. Analysis of the emission intensities from the neutral Na cloud suffers the complication that the emission seen is from the resonant scattering of sunlight; the emission intensity thus depends on the received solar flux at the wavelength of the atomic transition, and therefore, on the heliocentric velocity of the Na atoms [J. T. Bergstralh, J. W. Young, D. L. Matson, T. V. Johnson, Astrophys. J. 211, L51 (1977); R. A. Brown and Y. L. Yung, in Jupiter, T. Gehrels, Ed. (Univ. of Arizona Press, Tucson, 1976), pp. 1102-1145]. This effect is dependent mostly on lo's orbital phase, so we correct by removing the sliding-average modulation of the data at lo's orbital period. The total modulation by lo phase is 50%.
16. + density), as the emission is due to the electron impact excitation of the S. Analysis of the emission intensities from the neutral Na cloud suffers the complication that the emission seen is from the resonant scattering of sunlight; the emission intensity thus depends on the received solar flux at the wavelength of the atomic transition, and therefore, on the heliocentric velocity of the Na atoms [J. T. Bergstralh, J. W. Young, D. L. Matson, T. V. Johnson, Astrophys. J. 211, L51 (1977); R. A. Brown and Y. L. Yung, in Jupiter, T. Gehrels, Ed. (Univ. of Arizona Press, Tucson, 1976), pp. 1102-1145]. This effect is dependent mostly on lo's orbital phase, so we correct by removing the sliding-average modulation of the data at lo's orbital period. The total modulation by lo phase is 50%.
17. + density), as the emission is due to the electron impact excitation of the S. Analysis of the emission intensities from the neutral Na cloud suffers the complication that the emission seen is from the resonant scattering of sunlight; the emission intensity thus depends on the received solar flux at the wavelength of the atomic transition, and therefore, on the heliocentric velocity of the Na atoms [J. T. Bergstralh, J. W. Young, D. L. Matson, T. V. Johnson, Astrophys. J. 211, L51 (1977); R. A. Brown and Y. L. Yung, in Jupiter, T. Gehrels, Ed. (Univ. of Arizona Press, Tucson, 1976), pp. 1102-1145]. This effect is dependent mostly on lo's orbital phase, so we correct by removing the sliding-average modulation of the data at lo's orbital period. The total modulation by lo phase is 50%.
18. + density), as the emission is due to the electron impact excitation of the S. Analysis of the emission intensities from the neutral Na cloud suffers the complication that the emission seen is from the resonant scattering of sunlight; the emission intensity thus depends on the received solar flux at the wavelength of the atomic transition, and therefore, on the heliocentric velocity of the Na atoms [J. T. Bergstralh, J. W. Young, D. L. Matson, T. V. Johnson, Astrophys. J. 211, L51 (1977); R. A. Brown and Y. L. Yung, in Jupiter, T. Gehrels, Ed. (Univ. of Arizona Press, Tucson, 1976), pp. 1102-1145]. This effect is dependent mostly on lo's orbital phase, so we correct by removing the sliding-average modulation of the data at lo's orbital period. The total modulation by lo phase is 50%.
19. We estimated the total mass increase in the plasma torus by summing all emission along the slit and taking the square root, as the emission intensity is proportional to the product of the ion density and the electron density, which we assume scale together. Figure 2 appears to imply an even larger change in mass only because of the structural changes that occur in the torus at the same time.
20. An alternative scenario might be envisioned where the increase in mass of the neutral Na cloud is caused by an increase in the Na lifetime caused, for example, by a decrease in the electron temperature. We reject this hypothesis for two reasons: (i) Observations of the plasma torus, while not directly sensitive to electron temperature, show no change in the plasma torus mass, ion temperature, or rotation velocity at the start of the neutral Na cloud perturbation, and (ii) the increase in mass of the plasma torus shows that for S, at least, the supply increases precisely when the Na mass increases, strongly suggesting that the Na mass increase is caused by a Na supply increase.
21. C. B. Pilcher, J. H. Fertel, J. S. Morgan, Astrophys. J. 207, 181 (1980); A. J. Dessler and B. R. Sandel, Geophys. Res. Lett. 19, 2099 (1992); N. M. Schneider and J. T. Trauger, Astrophys. J. 450, 450 (1995).
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25. The lack of a shift on the duskside is unexpected. If the electric field operates uniformly across the magnetic field both sides should shift equally. The exclusively dawnside shift suggests that the electric field variations occur only on the dawn, explaining these data and also the sporadic dawnside shifts observed in imaging data (76).
26. J.
27. We are indebted to A. J. Dessler for the analogy to terrestrial equatorial currents and for the suggestion of the form of the relationship between an increasing plasma outflow and an increasing electric field.
28. dusk are tne position of the peak of plasma torus intensity on the dawn and dusk sides, respectively. As above, the relative density is estimated by the square root of the total intensity integrated along the spectral slit. The theoretical curves are calculated assuming zero electric field for a zero mass plasma torus and by forcing the curves to go through the equilibrium mass point (relative torus mass of 1.0).
29. The models of the behavior of the neutral cloud and magnetosphere mass are based on the zero-dimensional models of T. S. Huang and G. L. Siscoe [J. Geophys. Res. 91, 10163 (1986)]. For the supply-limited case, supply to the neutral cloud is proportional to the square root of the plasma density, and diffusive loss from the magnetosphere is proportional to the plasma density. For the loss-limited case, supply to the neutral cloud is proportional to the plasma density, and loss from the magnetosphere is proportional to the fourth power of the plasma density. For both cases, model input parameters are adjusted to yield a steady-state plasma lifetime of 30 days and a neutral lifetime of 20 hours.
30. Direct imaging of a new plume at the time of the outburst would provide conclusive proof of this hypothesis, but the capability of obtaining such an image was not available at the time of these observations. Ground-based infrared observations are able to monitor hotspot activity on lo, but we have no reason to expect that these are associated with plumes on lo, nor were any observations obtained during the outburst [G. J. Veeder, D. L. Matson, T. V. Johnson, D. L. Blaney, J. D. Goguen, ibid. 99, 17095 (1994)].
31. See, for example, E. Lellouch, Icarus 124, 1 (1996).
32. W. H. Smyth and M. R. Combi, Astrophys. J. 328, 888 (1988).
33. D. F. Strobel, in (5), pp. 183-195.
34. We benefited greatly from conversations with A. J. Dessler, T. W. Hill, M. A. McGrath, E. J. Moyer, and D. H. Pontius. This research would not have been begun without a generous seed grant from the California Space Institute and would not have proceeded without the reliable help of A. Misch and the other staff at Lick Observatory.