Earth has spectacular displays of aurora, the light shows unleashed when solar wind and plasma interact in the atmosphere. When it comes to sheer scale, however, they’ve got nothing on Jupiter, which is the home of the strongest planetary magnetic field in the solar system. Over the past couple of decades, scientists have used both telescopes and satellites to take stunning images of arcs of ultraviolet light shimmering around the gas giant’s poles.
Unlike Earth’s aurora, the Jovian auroras are nearly continuous, driven by the planet’s fast rotation and its volcanic moon Io, which spews sulfur and oxygen ions and electrons out into space. These electrons race along the planet’s magnetic field and, if they’re powerful enough, slam into the atmosphere and cause air molecules to glow.
But Jupiter’s auroras aren’t static—they swell and recede, pulsing at times with bursts of light lasting hours or even days. These variations are a clue to unraveling the physics in Jupiter’s magnetic field.
Tao et al. observed Jupiter’s aurora with the Japanese space telescope Hisaki, measuring the variations in brightness. They saw two kinds of auroral pulses. In one, the aurora brightened for up to several days at a time. The authors think this brightening is due to the solar wind: as it washes over the planet, the charged particles buffet and compress Jupiter’s magnetic field—similar to what happens on Earth.
But they also saw much faster variations, pulses lasting less than 10 hours. By comparing the Hisaki observations with images taken simultaneously by NASA’s Hubble Space Telescope, the team could see that this type of pulse was due to the aurora brightening at lower latitudes, at the bottom of the auroral arc, as reported by Kimura et al. .
Using Hisaki’s onboard spectrometer, the team was also able to estimate how fast the electrons were traveling on the basis of how deep in the atmosphere the light was originating. They found that when the aurora flares up, it’s not because faster, more powerful electrons are penetrating deeper into Jupiter’s atmosphere. Instead, the flaring is due to an increase in the overall number of electrons. This suggests that Jupiter’s most intense auroras occur when plasma is suddenly injected into its magnetic field—most likely from Io. (Journal of Geophysical Research: Space Physics, doi:10.1002/2015JA021272, 2015)
—Mark Zastrow, Freelance Writer
Citation: Zastrow, M. (2015), What makes Jupiter’s aurora pulse?, Eos, 96, doi:10.1029/2015EO039171. Published on 13 November 2015.