Enigma of Jupiter’s powerful auroras

Enigma of Jupiter’s powerful auroras:

This is a reconstructed view of Jupiter’s northern lights through the filters of the Juno Ultraviolet Imaging Spectrograph instrument on Dec. 11, 2016, as the Juno spacecraft approached Jupiter, passed over its poles, and plunged toward the equator. Such measurements present a real challenge for the spacecraft’s science instruments: Juno flies over Jupiter’s poles at 30 miles (50 kilometers) per second – more than 100,000 miles per hour (44.7 km/s) – speeding past auroral forms in a matter of seconds. Image & Caption Credit: Bertrand Bonfond / NASA / JPL-Caltech

On Earth, the swirling, entrancing beauty of the auroras, which are generally isolated to the polar regions of the planet, are fairly well-understood processes. These visual light shows are caused by the interaction of charged particles from the Sun interacting with particles in the atmosphere along the area where the Earth’s magnetosphere, a protective magnetic bubble that is generated deep within the core of the planet, surrounds and connects to the Earth’s dipoles (magnetic north and south poles). This same understanding of auroral processes cannot be said of the incredibly powerful Jovian auroras observed by NASA’s Juno spacecraft.

A new paper, published in the September 7th edition of the journal Nature, confirms data from the Juno spacecraft which indicates that Jupiter’s auroras are being generated by a mysterious process instead of being produced by the interaction of particles from the solar wind with the magnetosphere, as they are on Earth.

This image, created with data from Juno’s Ultraviolet Imaging Spectrograph, marks the path of Juno’s readings of Jupiter’s auroras, highlighting the electron measurements that show the discovery of the so-called discrete auroral acceleration processes indicated by the “inverted Vs” in the lower panel. Image & Caption Credit: Randy Gladstone / NASA / JPL-Caltech / SwRI

The auroral process on Jupiter, whereby electrons are being accelerated toward the planet’s atmosphere and then shot up out of the atmosphere aligned along the magnetic field lines at energies of up to 400,000 electron volts, is 10–30 times higher than the most intense auroras – known as discrete auroras – observed in Earth’s polar regions.

The Juno spacecraft, which has been in orbit around Jupiter since July 4, 2016, has been gathering some spectacular images and data for more than a year. The data has given scientists huge mysteries to solve along with the insights they have received regarding the intense processes occurring within the gas giant.

At a press conference on May 25, 2017, Scott Bolton, the principal investigator of the Juno mission, said: “There is so much going on here that we didn’t expect that we have had to take a step back and begin to rethink of this as a whole new Jupiter.”

Jupiter’s auroras are definitely one of those unexpected areas.

The Jupiter Energetic-particle Detector Instrument (JEDI) on NASA’s Juno spacecraft was built by Johns Hopkins University’s Applied Physics Laboratory (JHU-APL). Barry Mauk who leads the team working on the ultraviolet spectroscopy and energetic particle detection instruments, observed signatures of extremely powerful electric potentials.

The extreme power of the signatures wasn’t overly surprising considering the extreme nature of nearly everything at Jupiter, but what was very surprising was the movement of the particles and trying to determine where and how they are being generated.

Whereas Earth auroras are driven by particles moving downward into the poles of the magnetosphere, Jupiter’s auroras are caused by stochastic, or turbulent, unpredictable acceleration processes that end up accelerating particles out of Jupiter’s magnetic north pole.

“At Jupiter, the brightest auroras are caused by some kind of turbulent acceleration process that we do not understand very well,” said Mauk. “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.”

Jupiter has become a sort of physics lab for worlds outside of the Solar System. The giant planet’s ability to accelerate these charged particles to such huge energies gives scientists ideas and understanding for how worlds in far distant stellar planetary systems may also accelerate particles. The forces that are driving the Jovian auroras also give hints and suggestions about space weather and its impact on Earth as well as on other bodies in the Solar System and beyond.

In addition, Mauk said: “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 a challenge to Juno and to upcoming missions to Jupiter under development. 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.”

The images contain intensities from three spectral ranges, false-colored red, green, and blue, providing qualitative information on precipitating electron energies (high, medium, and low, respectively). An estimate of the magnetic projections of the Juno trajectory is shown (red lines), determined using the VIPAL24 magnetic field model with large uncertainties, with tick marks in steps of 1 h (see Methods). The short yellow arcs with arrows indicate the direction to the Sun when the image was taken. The blue-green lines are the average positions of the main ultraviolet aurora for the south and north, respectively. (a) Jupiter’s southern aurora taken during the fourth perijove (PJ4) encounter on 2 February 2017. (b) Jupiter’s northern aurora taken during the third perijove (PJ3) encounter on 11 December 2016. Image & Caption Credit: B. H. Mauk et al. / Nature

NASA’s Jet Propulsion Laboratory (JPL), Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute (SwRI) 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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