Jupiter's Aurora
Credit X-ray: NASA/CXC/UCL/W.Dunn et al, Optical: South Pole: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt /Seán Doran; North Pole: NASA/JPL-Caltech/SwRI/MSSS
Jupiter's intense northern and southern lights, or auroras, behave independently of each other according to a new study using NASA's Chandra X-ray and ESA's XMM-Newton observatories.
Using XMM-Newton and Chandra X-ray observations from March 2007 and
May and June 2016, a team of researchers produced maps of Jupiter's
X-ray emissions and identified an X-ray hot spot at each pole. Each hot spot can cover an area equal to about half the surface of the Earth.
The team found that the hot spots had very different characteristics. The X-ray emission at Jupiter's south pole consistently pulsed every 11 minutes, but the X-rays seen from the north pole were erratic, increasing and decreasing in brightness — seemingly independent of the emission from the south pole.
This makes Jupiter particularly puzzling. X-ray auroras have never been detected from our Solar System's other gas giants, including Saturn.
Jupiter is also unlike Earth, where the auroras on our planet's north
and south poles generally mirror each other because the magnetic fields
are similar.
To understand how Jupiter produces its X-ray auroras, the team of
researchers plans to combine new and upcoming X-ray data from Chandra
and XMM-Newton with information from NASA's Juno mission, which is
currently in orbit around the planet. If scientists can connect the
X-ray activity with physical changes observed simultaneously with Juno,
they may be able to determine the process that generates the Jovian
auroras and by association X-ray auroras at other planets.
Illustration of Jupiter
Credit: NASA/CXC/M.Weiss
One theory that the X-ray and Juno observations may help to prove or
disprove is that Jupiter's X-ray auroras are caused by interactions at
the boundary between Jupiter's magnetic field, which is generated by
electrical currents in the planet's interior, and the solar wind, a
high-speed flow of particles streaming from the Sun. The interactions
between the solar wind
and Jupiter's magnetic field can cause the latter to vibrate and
produce magnetic waves. Charged particles can surf these waves and gain
energy. Collisions of these particles with Jupiter's atmosphere produce
the bright flashes of X-rays observed by Chandra and XMM. Within this
theory the 11-minute interval would represent the time for a wave to
travel along one of Jupiter's magnetic field lines.
The difference in behavior between the Jovian north and south poles
may be caused by the difference in visibility of the two poles. Because
the magnetic field of Jupiter is tilted, we are able to see much more of
the northern aurora than the southern aurora. Therefore for the north
pole we may be able to observe regions where the magnetic field connects
to more than one location, with several different travel times, while
for the south pole we can only observe regions where the magnetic field
connects to one location. This would cause the behavior of the north
pole to appear erratic compared to the south pole.
A larger question is how does Jupiter give the particles in its magnetosphere
(the realm controlled by Jupiter's magnetic field) the huge energies
needed to make X-rays? Some of the X-ray emission observed with Chandra
can only be produced if Jupiter accelerates oxygen ions to such high
energies that when they violently collide with the atmosphere all eight
of their electrons are torn off. Scientists hope to determine what
impact these particles, which crash into the planet's poles at thousands
of kilometers per second, have on the planet itself. Do these
high-energy particles affect the Jovian weather and the chemical
composition of its atmosphere? Can they explain the anomalously high
temperatures found in certain places in Jupiter's atmosphere? These are
the questions that Chandra, XMM-Newton, and Juno may be able to help
answer in the future.
A paper describing these results
appeared in the October 30th issue of Nature Astronomy, led by William
Dunn of the University College London. NASA's Marshall Space Flight
Center in Huntsville, Alabama, manages the Chandra program for NASA's
Science Mission Directorate in Washington. The Smithsonian Astrophysical
Observatory in Cambridge, Massachusetts, controls Chandra's science and
flight operations.
Fast Facts for Jupiter:
Scale: This image is about 37 arcsec across (139,822 km = Jupiter's diameter) as viewed from Earth
Category: Solar System
Observation Date: May 24 & Jun 01, 2016
Observation Time: 22 hours
Obs. ID: 18608 & 18609
Instrument: HRC
References: Dunn, W.R. et al, 2017, Nature Astronomy, 1, 758
Color Code: X-ray (purple), optical (pseudocolor)
Distance Estimate: About 793 million km (on date of Chandra observations)
Source: NASA’s Chandra X-ray Observatory
