Ribbon wraps up mystery of Jupiters magnetic equator

The discovery of a dark ribbon of weak hydrogen ion emissions that encircles Jupiter has overturned previous thinking about the giant planet’s magnetic equator.

An international team of scientists led by Dr Tom Stallard from the Department of Physics and Astronomy has identified the weakened ribbon of H₃⁺ emissions near the jovigraphic equator using the NSFCam instrument at the NASA InfraRed Telescope Facility. Published online by Nature Astronomy today, it marks the first evidence of a localised ionospheric interaction with Jupiter’s magnetic field.

Watch video of a projection of the map of Jupiter’s ionosphere, highlighting the aurorae, Great Cold Spot and magnetic equator:

In the past, studies of Jupiter’s ionosphere have almost exclusively focused on the poles of the planet, looking at the aurorae. These observations saw most of Jupiter’s ionosphere as relatively smooth and uninteresting.

This latest study has opened up the entire ionosphere for investigation and suggests that Jupiter’s ionosphere is as complex as our observations are able to measure with levels of details still yet to be revealed. It also demonstrates that, despite the differences in their size and structure, both Earth and Jupiter have a similar localised ribbon that winds its way around the magnetic equator of the planet. Recent data from NASA’s Juno spacecraft supports the theory that this ribbon is a signature for Jupiter’s magnetic equator.

The observations identified a number of other localised dark regions, including the area identified last year as the Great Cold Spot by the same team of scientists.

The ionosphere is the ionized part of Jupiter’s upper atmosphere. Here, collisions between photoelectrons and H₂ are a significant source of H₃⁺ ions.

One explanation for the dark ribbon is that because electrons preferentially travel along magnetic field lines, these photoelectrons are diverted to higher latitudes from the magnetic equator as they move to lower altitudes – leaving behind the ribbon of reduced H₃⁺production.

• Press release
• 'Identification of Jupiter’s magnetic equator through H3+ ionospheric emission' is published by Nature Astronomy on 23 July 2018. DOI: 10.1038/s41550-018-0523-z
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