Advertisement

Sheath Acceleration of Photoelectrons by Jupiter’s Satellite Io

  • Stanley D. Shawhan
  • Richard F. Hubbard
  • Glenn Joyce
  • Donald A. Gurnett
Part of the Astrophysics and Space Science Library book series (ASSL, volume 37)

Abstract

We are investigating a model of the influence of Jupiter’s moon Io on Jovian decametric radiation due to plasma sheaths formed around Io’s surface. With Io, we are dealing with a large, partially-conducting, and photoemitting body with a large V × B potential (~ 700000 Volts) across its diameter. A well-known model by Goldreich and Lyden-Bell (1969) assumes Jupiter’s field lines are frozen to Io, while we are proposing instead that sheaths form around Io and electrons are accelerated across these sheaths.

Two types of sheaths are considered. A Debye sheath forms around regions of Io’s surface which are negative with respect to the plasma potential while a photoelectron sheath forms where the surface potential is positive. The Debye sheath (of area A p ) accelerates emitted photoelectrons away from the surface (with current density J p ) while the photoelectron sheath (of area A e ) collects an ambient electron current (J e A e ). The current balance is J p A p = J e A e . The boundary between the two regions has zero potential.

We estimate J e and J p to be 3 × 10−7 A m−2, but both may vary considerably. The emitted particle spectrum is critically dependent on the ratio J e /J p . Estimates of total power available in the accelerated photoelectrons are 1010–1013 W, well above the 107 W contained in a typical decametric burst. We have also studied the effect of Io’s orbital position on our model since decametric bursts are strongly coupled to Io’s position.

Although E is probably radial through the sheath, we believe that the electron gyroradius is small compared with sheath dimensions so that the particles emerge almost parallel to Jupiter’s field lines. Using an ‘oblique’ version of Child’s Law, we estimate the typical sheath thickness as 10–50 km. High energy (up to several hundred keV) electrons thus travel along B field lines and eventually produce the observed radio noise.

Keywords

Field Line Runaway Electron Plasma Sheath Ionospheric Conductivity Sheath Region 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Bigg, E. K.: 1964, Nature 203, 1008.ADSCrossRefGoogle Scholar
  2. Block, Lars P.: 1972, submitted to Cosmic Electrodyn. 3.Google Scholar
  3. Criswell, David R.: 1971, EOS 52, 855.Google Scholar
  4. Dermott, S. F.: 1970, Monthly Notices Roy. Astron. Soc. 149, 35.ADSGoogle Scholar
  5. Duncan, R. A.: 1970, Planetary Space Sci. 18, 217.ADSCrossRefGoogle Scholar
  6. Gledhill, J. A.: 1967, Nature 214, 155.ADSCrossRefGoogle Scholar
  7. Goldreich, P. and Lynden-Bell, D.: 1969, Astrophys. J. 156, 56.ADSCrossRefGoogle Scholar
  8. Gross, R. H. and Rasool, S. I.: 1964, Icarus 3, 311.ADSCrossRefGoogle Scholar
  9. Gurnett, Donald A.: 1972, Astrophys. J. 175, 525.ADSCrossRefGoogle Scholar
  10. Ioannidis, G. and Brice, N.: 1971, Icarus 14, 360.ADSCrossRefGoogle Scholar
  11. Lewis, John S.: 1971, Icarus 15, 174.ADSCrossRefGoogle Scholar
  12. Mozer, F. S. and Bogott, F. H.: 1972, Astrophys. J. 174, 153.ADSCrossRefGoogle Scholar
  13. Piddington, J. H. and Drake, J. F.: 1968, Nature 217, 935.ADSCrossRefGoogle Scholar
  14. Piddington, J. H.: 1972, Cosmic Electrodyn. 3, 240.Google Scholar
  15. Prasad, S. S. and Capone, L. A.: 1971, Icarus 15, 45.ADSCrossRefGoogle Scholar
  16. Reasoner, David L. and Burke, William J.: 1971, ‘Direct Observation of the Lunar Photoelectron Layer’, preprint Dept. of Space Science, Rice University.Google Scholar
  17. Schatten, K. H. and Ness, N. F.: 1971, Astrophys. J. 165, 621.ADSCrossRefGoogle Scholar
  18. Warwick, J. W. and Dulk, G. A.: 1964, Science 145, 380.ADSCrossRefGoogle Scholar

Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1973

Authors and Affiliations

  • Stanley D. Shawhan
    • 1
  • Richard F. Hubbard
    • 1
  • Glenn Joyce
    • 1
  • Donald A. Gurnett
    • 1
  1. 1.Dept. of Physics and AstronomyThe University of IowaIowa CityUSA

Personalised recommendations