Researchers look at Hubble images to spot secondary arcs of Jupiter’s aurora.
Auroras shine bright blue over Jupiter. Credit: NASA, ESA
Source: Journal of Geophysical Research: Space Physics

Perhaps the most distinguishable feature of any planet in the solar system is Jupiter’s Great Red Spot: a swirling storm of gases twice the size of Earth. In recent years, using the Hubble Space Telescope, scientists have been able to study yet another rare and beautiful atmospheric phenomenon of this gas giant: auroras.

Jupiter’s auroras, just like the northern lights, form when high-energy particles enter the atmosphere near the poles and collide with gas atoms, producing an eerie glow.

Astronomers studying these extraterrestrial auroras have mapped out several main regions: the central emission (also known as the main auroral oval), two polar emissions near each of the poles, and outer emissions. The outer emissions, in turn, are made up of moon footprints (bright spots caused by electric current from Jupiter’s moons), injections of hot plasma, and a second auroral oval. This secondary oval, located closer to the equator than the main oval, becomes visible to earthly observers when hot plasma injections act as a source of energy for wave-particle interactions, setting the region alight.

In a recent study, Gray et al. surveyed the secondary auroral oval with greater insight than ever before by examining images taken from Hubble’s Space Telescope Imaging Spectrograph in the first 16 days of 2014.

The researchers identified an aurora formation—an arc of ultraviolet light—located in the secondary auroral oval. The arc lies between two moon footprints, Ganymede and Europa, corresponding to an area called the pitch angle distribution (PAD) boundary in the region around Jupiter. Beyond the PAD boundary, scientists believe, electrons are scattered in a pattern causing auroral precipitation.

Auroras leave behind signatures that allow scientists to retroactively determine the energy levels of the scattering electrons. Through the images they studied, the authors found that the auroral arc became bigger and brighter in the few days after a large plasma injection. They also found that the electrons causing auroral precipitation had higher energy and smaller fluctuations than the electrons generating large plasma injections.

The researchers concluded that the scattering of electrons in the secondary auroral oval is caused by wave-particle interactions. They also believe plasma injections can cause temperature changes and enhance wave intensity, scattering electrons into the upper atmosphere for days at a time. Overall, the study tells us more about the nearby gas giant and the far-reaching activities of its vivid auroras. (Journal of Geophysical Research: Space Physics,, 2017)

—Sarah Witman, Freelance Writer


Witman, S. (2017), Hubble reveals less studied regions of Jupiter’s auroras, Eos, 98, Published on 25 July 2017.

Text © 2017. The authors. CC BY-NC-ND 3.0
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