Cassini observations of Io's visible aurorae

Paul Geissler, Alfred S. McEwen, Carolyn Porco, Darrell Strobel, Joachim Saur, Joseph Ajello, Robert West

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

More than 500 images of Io in eclipse were acquired by the Cassini spacecraft in late 2000 and early 2001 as it passed through the jovian system en route to Saturn (Porco et al., 2003, Science 299, 1541-1547). Io's bright equatorial glows were detected in Cassini's near-ultraviolet filters, supporting the interpretation that the visible emissions are predominantly due to molecular SO2. Detailed comparisons of laboratory SO2 spectra with the Cassini observations indicate that a mixture of gases contribute to the equatorial emissions. Potassium is suggested by new detections of the equatorial glows at near-infrared wavelengths from 730 to 800 nm. Neutral atomic oxygen and sodium are required to explain the brightness of the glows at visible wavelengths. The molecule S2 is postulated to emit most of the glow intensity in the wavelength interval from 390 to 500 nm. The locations of the visible emissions vary in response to the changing orientation of the external magnetic field, tracking the tangent points of the jovian magnetic field lines. Limb glows distinct from the equatorial emissions were observed at visible to near-infrared wavelengths from 500 to 850 nm, indicating that atomic O, Na, and K are distributed across Io's surface. Stratification of the atmosphere is demonstrated by differences in the altitudes of emissions at various wavelengths: SO2 emissions are confined to a region close to Io's surface, whereas neutral oxygen emissions are seen at altitudes that reach up to 900 km, or half the radius of the satellite. Pre-egress brightening demonstrates that light scattered into Jupiter's shadow by gases or aerosols in the giant planet's upper atmosphere contaminates images of Io taken within 13 minutes of entry into or emergence from Jupiter's umbra. Although partial atmospheric collapse is suggested by the longer timescale for post-ingress dimming than pre-egress brightening, Io's atmosphere must be substantially supported by volcanism to retain auroral emissions throughout the duration of eclipse.

Original languageEnglish (US)
Pages (from-to)127-140
Number of pages14
JournalIcarus
Volume172
Issue number1 SPEC.ISS.
DOIs
StatePublished - Nov 2004

Fingerprint

Io
aurora
wavelength
egress
wavelengths
eclipses
Jupiter (planet)
Jupiter
near infrared
ultraviolet filters
umbras
magnetic field
atmospheres
dimming
oxygen
atmosphere
upper atmosphere
Saturn
stratification
limbs

Keywords

  • Atmospheres
  • Aurorae
  • Io
  • Satellites

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Geissler, P., McEwen, A. S., Porco, C., Strobel, D., Saur, J., Ajello, J., & West, R. (2004). Cassini observations of Io's visible aurorae. Icarus, 172(1 SPEC.ISS.), 127-140. https://doi.org/10.1016/j.icarus.2004.01.008

Cassini observations of Io's visible aurorae. / Geissler, Paul; McEwen, Alfred S.; Porco, Carolyn; Strobel, Darrell; Saur, Joachim; Ajello, Joseph; West, Robert.

In: Icarus, Vol. 172, No. 1 SPEC.ISS., 11.2004, p. 127-140.

Research output: Contribution to journalArticle

Geissler, P, McEwen, AS, Porco, C, Strobel, D, Saur, J, Ajello, J & West, R 2004, 'Cassini observations of Io's visible aurorae', Icarus, vol. 172, no. 1 SPEC.ISS., pp. 127-140. https://doi.org/10.1016/j.icarus.2004.01.008
Geissler P, McEwen AS, Porco C, Strobel D, Saur J, Ajello J et al. Cassini observations of Io's visible aurorae. Icarus. 2004 Nov;172(1 SPEC.ISS.):127-140. https://doi.org/10.1016/j.icarus.2004.01.008
Geissler, Paul ; McEwen, Alfred S. ; Porco, Carolyn ; Strobel, Darrell ; Saur, Joachim ; Ajello, Joseph ; West, Robert. / Cassini observations of Io's visible aurorae. In: Icarus. 2004 ; Vol. 172, No. 1 SPEC.ISS. pp. 127-140.
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