Tuesday, July 24, 2018

'Ribbon’ Wraps Up Mystery of Jupiter’s Magnetic Equator

New data from Jupiter observations is a gift to Leicester astronomers

Map of the infrared brightness of H3+ ions at the top of Jupiter’s atmosphere, The dark ribbon around the horizontal centre of the image reveals the location of Jupiter’s 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.

This image is a map of the infrared brightness of H3+ ions at the top of Jupiter's atmosphere reveals just how complex the ionosphere is. The two white regions at the top and bottom are the planet's brilliant aurora. Glowing vastly brighter than the rest of the planet, they are here so saturated that no details can be see at all. Instead, the equatorial region can be seen. In the top left of the map, the previously observed darkening associated with the Great Cold Spot can be seen -- the map now shows that this dark feature is only one of many within the ionosphere. The dark ribbon that undulates around the horizontal center of the image, wrapping around the planet from left to right, reveals the location of Jupiter's magnetic equator. To the right of the image, above and below the dark ribbon, there are two very dark regions, a larger one in the north and a small circle in the south. We are not completely sure what these features are, but when the Juno spacecraft measured the magnetic fields in these regions, they were shown to be highly anomalous -- perhaps these regions are similar to the Southern Atlantic magnetic anomaly on Earth.

Credit: University of Leicester

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:

Credit: University of Leicester

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.

 Three different measurements of Jupiter’s magnetic equator: the first, in blue, is the best past estimate of what was thought to be the equator using ultraviolet light; the second, in red and yellow is the location of the dark ribbon seen in this map; the third is the new measurement of the magnetic equator recently measured by the Juno spacecraft.

Credit: University of Leicester

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.

Contacts and sources:
Dr Tom Stallard
University of Leicester

Citation:  '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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