Juno and Hubble data reveal electromagnetic 'tug-of-war' lights up
Jupiter's upper atmosphere

Date:
February 3, 2022
Source:
University of Leicester
Summary:
New space research has revealed a complex 'tug-of-war' lights up
aurorae in Jupiter's upper atmosphere. The study describes the
delicate current cycle driven by Jupiter's rapid rotation and the
release of sulphur and oxygen from volcanoes on its moon, Io.



FULL STORY ==========================================================================
New Leicester space research has revealed, for the first time, a complex
'tug- of-war' lights up aurorae in Jupiter's upper atmosphere, using a combination of data from NASA's Juno probe and the Hubble Space Telescope.


==========================================================================
The study, published in the Journal of Geophysical Research: Space
Physics, describes the delicate current cycle driven by Jupiter's rapid rotation and the release of sulphur and oxygen from volcanoes on its
moon, Io.

Researchers from the University of Leicester's School of Physics and
Astronomy used data from Juno's Magnetic Field Investigation (MAG),
which measures Jupiter's magnetic field from orbit around the gas giant,
and observations from the Space Telescope Imaging Spectrograph carried
by the Hubble Space Telescope.

Their research provides the strongest evidence yet that Jupiter's powerful aurorae are associated with an electric current system that acts as part
of a tug-of-war with material in the magnetosphere, the region dominated
by the planet's enormous magnetic field.

Dr Jonathan Nichols is a Reader in Planetary Auroras at the University
of Leicester and corresponding author for the study. He said: "We've
had theories linking these electric currents and Jupiter's powerful
auroras for over two decades now, and it was so exciting to be able to
finally test them by looking for this relationship in the data. And when
we plotted one against the other I nearly fell off my chair when I saw
just how clear the connection is.



========================================================================== "It's thrilling to discover this relation because it not only helps
us understand how Jupiter's magnetic field works, but also those of
planets orbiting other stars, for which we have previously used the same theories, and now with renewed confidence." Despite its huge size --
with a diameter more than 11 times that of Earth - - Jupiter rotates
once approximately every nine-and-a-half hours.

Io is a similar size and mass to Earth's moon, but orbits Jupiter at
an average distance of 422,000 km; roughly 10% further away. With over
400 active volcanoes, Io is the most geologically active object in the
Solar System.

Scientists had long suspected a relationship between Jupiter's aurorae
and the material ejected from Io at a rate of many hundreds of kilograms
per second, but the data captured by Juno proved ambiguous.

Dr Scott Bolton, of NASA's Jet Propulsion Laboratory (JPL), is Principal Investigator (PI) for the Juno mission. He said: "These exciting results
on how Jupiter's aurorae work are a testament to the power of combining Earth-based observations from Hubble with Juno measurements.

The HST images provide the broad overview, while Juno investigates
close up.

Together they make a great team!"


==========================================================================
Much of the material released from Io is propelled away from Jupiter by
the planet's rapidly rotating magnetic field, and as it moves outward
its rotation rate tends to slow down. This results in an electromagnetic tug-of-war, in which Jupiter attempts to keep this material spinning
at its rotation speed via a system of electric currents flowing through
the planet's upper atmosphere and magnetosphere.

The component of the electric current flowing out of the planet's
atmosphere, carried by electrons fired downward along magnetic field
lines into the upper atmosphere, was thought to drive Jupiter's main
auroral emission.

However, prior to Juno's arrival this idea had never been tested, as no spacecraft with relevant instruments had previously orbited close enough
to Jupiter. And when Juno arrived in 2016, the expected signature of such
an electric current system was not reported -- and, while such signatures
have since been found -- one of the great surprises of Juno's mission
has been to show that the nature of the electrons above Jupiter's polar
regions is much more complex than was initially expected.

The researchers compared the brightness of Jupiter's main auroral emission
with simultaneous measurements of the electric current flowing away from
the Solar System's largest planet in the magnetosphere over an early
part of Juno's mission.

These aurorae were observed with instruments on board the Hubble Space Telescope, in Earth orbit. By comparing the dawn-side measurements of
current with the brightness of Jupiter's aurorae, the team demonstrated
the relationship between the auroral intensity and magnetospheric
current strength.

Stan Cowley is Emeritus Professor of Solar-Planetary Physics at the
University of Leicester and co-author for the study, and has studied
Jupiter's powerful aurorae for 25 years. Professor Cowley added:
"Having more than five years of in-orbit data from the Juno spacecraft, together with auroral imaging data from the HST, we now have the material
to hand to look in detail at the overall physics of Jupiter's outer
plasma environment, and more is to come from Juno's extended mission,
now in progress.

We hope our present paper will be followed by many more
exploring this treasure trove for new scientific understanding." ========================================================================== Story Source: Materials provided by University_of_Leicester. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* The_aurorae ========================================================================== Journal Reference:
1. J. D. Nichols, S. W. H. Cowley. Relation of Jupiter's Dawnside Main
Emission Intensity to Magnetospheric Currents During the Juno
Mission.

Journal of Geophysical Research: Space Physics, 2022; 127 (1)
DOI: 10.1029/2021JA030040 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220203083619.htm

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