Jupiter's Auroras Present a Powerful Mystery
Jet Propulsion Laboratory
September 6, 2017
Scientists on NASA's Juno mission have observed massive amounts of energy
swirling over Jupiter's polar regions that contribute to the giant planet's
powerful auroras - only not in ways the researchers expected.
Examining data collected by the ultraviolet spectrograph and energetic-particle
detector instruments aboard the Jupiter-orbiting Juno spacecraft, a team
led by Barry Mauk of the Johns Hopkins University Applied Physics Laboratory,
Laurel, Maryland, observed signatures of powerful electric potentials,
aligned with Jupiter's magnetic field, that accelerate electrons toward
the Jovian atmosphere at energies up to 400,000 electron volts. This is
10 to 30 times higher than the largest auroral potentials observed at
Earth, where only several thousands of volts are typically needed to generate
the most intense auroras -- known as discrete auroras -- the dazzling,
twisting, snake-like northern and southern lights seen in places like
Alaska and Canada, northern Europe, and many other northern and southern
Jupiter has the most powerful auroras in the solar system, so the team
was not surprised that electric potentials play a role in their generation.
What's puzzling the researchers, Mauk said, is that despite the magnitudes
of these potentials at Jupiter, they are observed only sometimes and are
not the source of the most intense auroras, as they are at Earth.
"At Jupiter, the brightest auroras are caused by some kind of turbulent
acceleration process that we do not understand very well," said Mauk,
who leads the investigation team for the APL-built Jupiter Energetic Particle
Detector Instrument (JEDI). "There are hints in our latest data indicating
that as the power density of the auroral generation becomes stronger and
stronger, the process becomes unstable and a new acceleration process
takes over. But we'll have to keep looking at the data."
Scientists consider Jupiter to be a physics lab of sorts for worlds beyond
our solar system, saying the ability of Jupiter to accelerate charged
particles to immense energies has implications for how more distant astrophysical
systems accelerate particles. But what they learn about the forces driving
Jupiter's auroras and shaping its space weather environment also has practical
implications in our own planetary backyard.
"The highest energies that we are observing within Jupiter's auroral regions
are formidable. These energetic particles that create the auroras are
part of the story in understanding Jupiter's radiation belts, which pose
such a challenge to Juno and to upcoming spacecraft missions to Jupiter
under development," said Mauk. "Engineering around the debilitating effects
of radiation has always been a challenge to spacecraft engineers for missions
at Earth and elsewhere in the solar system. What we learn here, and from
spacecraft like NASA's Van Allen Probes and Magnetospheric Multiscale
mission (MMS) that are exploring Earth's magnetosphere, will teach us
a lot about space weather and protecting spacecraft and astronauts in
harsh space environments. Comparing the processes at Jupiter and Earth
is incredibly valuable in testing our ideas of how planetary physics works."
Mauk and colleagues present their findings in the Sept. 7 issue of the
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Juno
mission for the principal investigator, Scott Bolton, of the Southwest
Research Institute in San Antonio. Juno is part of NASA's New Frontiers
Program, which is managed at NASA's Marshall Space Flight Center in Huntsville,
Alabama, for NASA's Science Mission Directorate. Lockheed Martin Space
Systems, Denver, built the spacecraft.
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Jet Propulsion Laboratory, Pasadena, Calif.
Johns Hopkins University Applied Physics Laboratory
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