First Inside Look at Hot and Cold Ions in Jupiter's Ionosphere
The first in-situ ion observations from NASA's Juno spacecraft reveal the surprising, simultaneous presence of cold protons and hot oxygen and sulfur ions in the high-latitude ionosphere of Jupiter.
SOURCE: Geophysical Research Letters
Left: The orbit path of the Juno spacecraft on Jupiter on 27 August 2016, as viewed from the Sun, with the ion observation periods in bold. Middle and Right: Observed ion energy and time-of-flight (TOF) spectra in the northern and southern hemisphere, showing the presence of cold protons and hot oxygen and sulfur ions, with the ion count rates in color codes. The black solid lines indicate the nominal locations for H+, O+, O++, S++, and S+++ ions on the spectrum; the red lines show the expected locations for H2+ and H3+. The dashed line indicates the transition energy between the ionospheric and magnetospheric ions. The ion counts at low energies and long TOF are contamination from the proton signal. Credit: Valek et al. [2019], adapted from Figure 1a and 2
The ion sensor on NASA's Juno spacecraft has made the first in situ observations in the upper portion of the Jupiter ionosphere. Valek et al. [2019] reveal, rather surprisingly, bands of cold ionospheric protons in both the Northern and Southern Hemispheres, in a region just equatorward of the auroral oval on Jupiter, with energies below an electron volt.
Even more surprisingly, these cold protons are seen to coincide with populations of hot oxygen and sulfur ions with energies of one to ten thousand electron volts, precipitating from Jupiter's inner magnetosphere. These hot, heavy ions are believed to heat the upper ionosphere, thereby raising the height of the cold protons and making them observable on Juno.
These unexpected observations shed important lights on how the dynamics of Jupiter's ionosphere and magnetosphere are coupled together.
Citation: Valek, P. W., Allegrini, F., Bagenal, F., Bolton, S. J., Connerney, J. E. P., Ebert, R. W., et al. [2019]. Jovian high‐latitude ionospheric ions: Juno in situ observations. Geophysical Research Letters, 46, 8663– 8670. https://doi.org/10.1029/2019GL084146
—Andrew Yau, Editor, Geophysical Research Letters
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