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UV Observations of the Io Plasma Torus from New Horizons and Rosetta

UV Observations of the Io Plasma Torus from New Horizons and Rosetta. Andrew J. Steffl 1 , M. F. A'Hearn 2 , J. L. Bertaux 3 , P. D. Feldman 4 , G. R. Gladstone 1 , J. W. Parker 1 , K. D. Retherford 1 , D. C. Slater 1 , S. A. Stern 5 , M. Versteeg 1 , H. A. Weaver 6

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UV Observations of the Io Plasma Torus from New Horizons and Rosetta

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  1. UV Observations of the Io Plasma Torus from New Horizons and Rosetta Andrew J. Steffl1, M. F. A'Hearn2, J. L. Bertaux3, P. D. Feldman4, G. R. Gladstone1, J. W. Parker1, K. D. Retherford1, D. C. Slater1, S. A. Stern5, M. Versteeg1, H. A. Weaver6 1SwRI, 2Univ. of Maryland, 3Service d'Aeronomie, 4JHU, 5NASA HQ, 6JHU-APL Presentation 4.09

  2. Alice UV Spectrometers • 4 “Alice” series UV spectrometers • Alice (R-Alice) on Rosettain flight • Alice (P-Alice) on New Horizons in flight • LAMP on LROdevelopment • UVS on Junodevelopment • Light-weight: • 3 kg (R-Alice); 4.4 kg (P-Alice) • Low-power: • 4 W (R-Alice); 4.4 W (P-Alice) • Wavelength Range: • 700-2050Å (R-Alice); 520-1870Å (P-Alice) • Spectral Resolution: • ~5Å FWHM (point source); ~10Å (Filled-slit) • Dispersion: ~1.8 Å/pixel • Detector: 1024x32-pixel Double Delay Line (DDL)

  3. The Jovian Magnetosphere from Rosetta • ESA’s Rosetta flew past Mars on 2007-02-25 (DOY 056) • On 2007-02-28 R-Alice began observations of the Jovian magnetosphere • Observations continued intermittently until 2007-05-08 (DOY128). • 378 hours of integration were acquired (1.36 Ms). • 4.2 AU from Jupiter, so no spatial resolution Jovian Aurora Reflected sunlight Torus emissions

  4. The Jovian Magnetosphere from Rosetta Alice 10-hour Averaged Luminosity • No obviously significant temporal variations in the IPT • Torus emissions ~2x fainter than during the Cassini epoch • Torus emissions possibly brighter DOY 120-130, though poor sampling • Jovian aurora significantly brighter on DOY 63, 69, 82

  5. The Jovian Magnetosphere from New Horizons Alice • New Horizons scan of aurora on 2007-03-03 • S/C at 22:15 local time;III= 170º • Scan approx. east from +3 to -6 RJ • Total scan time: 1800s • Sky in Alice “narrow” FOV for ~30s. • Data are time-tagged (pixel list mode)

  6. New Horizons Alice Spectral Images S III 680Å Io Plasma Torus Noon Ansa O II 834Å Sunlit Crescent of Jupiter H2 1600Å Jovian Aurora B Stars

  7. Iogenic neutrals (not modeled) Modeling the Io Plasma Torus Seen by P-Alice Torus mixing ratios (Nion/Ne) • High ionization states (S IV & O III) more abundant • Te ~ 3.5 eV vs. ~4.5 eV during Cassini epoch

  8. Conclusions • Both Rosetta Alice and New Horizons Alice observed the Jovian Magnetosphere • Observations yielded rich data sets • The Io plasma torus was 2x fainter in 2007 than the Cassini epoch of 2000-2001 • Torus electron temperatures ~ 4 eV • Significantly cooler than the Cassini epoch • Suggests (tentatively!) a lower rate of pickup ions • i.e. a lower amount of gas lost from Io’s atmosphere • Somewhat surprising given the amazing Tvashtar plume images • New Horizons Jupiter encounter data (through July 2007) available from the PDS Small Bodies Node 2007-11-01

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