Ground-based observations of Saturn’s H3+ aurora and ring rain from Keck in 2013

Abstract:

The ground-based 10-metre Keck telescope was used to probe Saturn’s H₃⁺ ionosphere in 2013. The slit on the high resolution near infrared spectrometer (NIRSPEC; (R~25,000) was aligned pole-to-pole along Saturn’s rotational axis at local noon. This is also aligned (within uncertainties) to the effectively dipolar magnetic field. Four polar/auroral regions of Saturn’s ionosphere were measured simultaneously as the planet rotated: 1) the northern noon main auroral oval; 2) the northern midnight main oval; 3) the northern polar cap and 4) the southern main oval at noon. The results here contain twenty-three H₃⁺ temperatures, column densities and total emissions located at the above regions spread over timescales of both hours and days. The main findings of this study are that ionospheric temperatures in the northern main oval are cooler than their southern counterparts by tens of K; supportive of the hypothesis that the total thermospheric heating rate (Joule heating and ion drag) is inversely proportional to magnetic field strength. The main oval H₃⁺ density and emission is lower at northern midnight than at noon, and this is in agreement with an electron influx peaking at 08:00 Saturn local time and having a minimum at midnight. When ordering the northern main oval parameters of H₃⁺ as a function of the oscillation period seen in Saturn’s magnetic field - the planetary period oscillation (PPO) phase - we see a large peak in H₃⁺ density and emission at ∼110° phase, with a full-width at half-maximum (FWHM) of ∼40°. This seems to indicate that the influx of electrons associated with the PPO phase at 90° is responsible at least in part for the behavior of all H₃⁺ parameters. In addition to the auroral/polar data we also present the latest results from observations of Saturn’s mid-to-low latitude H₃⁺ emission. This emission is thought to be modulated by charged water product influx which flows into the planet along magnetic field lines from Saturn’s rings, i.e. ring rain.

Figure:

H₃⁺ Q(1,0) parameters as a functon of northern PPO phase. The x- and y-axes show the PPO phase angle versus the H₃⁺ parameters in each of the four panels: a) Q(1,0) line intensity, b) temperature, c) column density and d) total emission. The blue, green and red correspond to the 19th, 20th and 21st of April, respectively.

Back to: In and Out of Jove: Giant Planet Interiors, Atmospheres, Aurorae, and Ionospheres I

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