【惑星科学】木星のオーロラに予想外のエネルギー源

Jupiter’s aurora behaves in a different way from Earth’s, according to a paper in this week’s Nature. Auroral emissions from Jupiter are much more powerful that those from Earth and thus they were thought to be generated by processes similar to those responsible for Earth’s strong auroral emissions. New observations made by NASA’s Juno mission suggest that this is not the case.

Earth’s auroras, also known as the southern or northern lights, are produced by interactions between charged particles from the Sun as they enter the atmosphere. Two processes are involved: intense auroras are generated by acceleration of electrons, whereas weaker aurora arise from scattering of magnetically trapped electrons. The former has been assumed to be the mechanism responsible for auroral emissions from Jupiter, although early observations from the Juno spacecraft found no evidence of this process. During subsequent flyovers, Juno has detected accelerating electrons, but this phenomenon does not seem to yield intense aurora, Barry Mauk and colleagues report. Instead, their observations indicate that Jupiter’s auroras are generated by processes similar to those responsible for Earth’s weaker aurora.

These findings provide insights into how different planets interact electromagnetically with their space environments. However, more data are needed to understand how these different processes work.