A new study conducted by University College London (UCL) using NASA's XMM-Newton observatories at NASA's ESA and Chandra-CXO to which Zhonghua YAO, a postdoctoral fellow at LPAP, contributed revealed that Very high energy X-ray emissions at Jupiter's South Pole pulsate regularly every 11 minutes. Meanwhile, those of the North Pole are erratic: they increase and decrease in brightness, independently of the South Pole. These observations were the subject of an article published in Nature Astronomy (1).
U
sing the XMM-Newton (ESA Space Observatory for soft X-ray observation) and Chandra (NASA X-ray Space Telescope) observatories, the international team of researchers, including one member of the University of Liège, produced maps of X-ray emissions at Jupiter poles and discovered that these emissions have very different characteristics from those observed on the Earth.
“We didn’t expect to see Jupiter’s X-ray hot spots pulsing independently as we thought their activity would be coordinated through the planet’s magnetic field. We need to study this further to develop ideas for how Jupiter produces its X-ray aurora and NASA’s Juno mission is really important for this,” explained lead author, William Dunn (UCL Mullard Space Science Laboratory, UK and the Harvard-Smithsonian Astrophysics, USA).
Since arriving at Jupiter in 2016, the Juno mission has been re-writing much of what is known about the giant planet, but there is no X-ray instrument on board the Spacecraft. To understand how the X-ray auroras are produced, the team now plans to combine the X-ray aurora information gathered using XMM-Newton and Chandra with data collected by Juno as it explores the regions producing Jupiter’s aurora.
This illustration shows the disc of Jupiter, observed with HST in visible light and the polar auroras RX, observed with Chandra, displayed in false violet colors. The more intense emission (hot spot) in the North appears as a whiter spot in the center of the dawn. The auroras appear simultaneously at the North Pole and at the South Pole, but for half a rotation the inclination of the magnetic field makes them more easily observable in the North.crédits: X-ray: NASA/CXC/UCL/W.Dunn et al, Optical: NASA/STScI.
"These observations imply that there is a new form of energy dissipation of charged particles in planetary systems. This process is not predicted by any existing theory, "says Zhonghua Yao, co-author of the article and postdoctoral fellow at the University of Liege. "XR and UV auroras are electromagnetic signatures that are most likely related. Therefore, it is crucial to determine the exact relationship between these emissions. This is obviously a job that will keep us very busy during the coming months. "
“If we can start to connect the X-ray signatures with the physical processes that produce them, then we can use those signatures to understand other bodies across the Universe such as brown dwarfs, exoplanets or maybe even neutron stars. It is a very powerful and important step towards understanding X-rays throughout the Universe and one that we only have while Juno is conducting measurements simultaneously with Chandra and XMM-Newton,” said William Dunn.
One of the theories that Juno may help to prove or disprove is that Jupiter’s auroras form separately when the planet’s magnetic field interacts with the solar wind. The team suspects that the magnetic field lines vibrate, producing waves that carry charged particles towards the poles and these change in speed and direction of travel until they collide with Jupiter’s atmosphere, generating X-ray pulses.
(1) W. R. Dunn, G. Branduardi-Raymont, L. C. Ray, C. M. Jackman, R. P. Kraft, R. F. Elsner, I. J. Rae, Z. Yao, M. F. Vogt, G. H. Jones, G. R. Gladstone, G. S. Orton, J. A. Sinclair, P. G. Ford, G. A. Graham, R. Caro-Carretero and A. J. Coates , ‘The independent pulsations of Jupiter’s northern and southern X-ray auroras’ will be published in Nature Astronomy, 30 October 2017.
One of the co-authors of this study, Dr. Zhonghua YAO, is a postdoctoral fellow at the Laboratory for Atmospheric and Planetary Physics (LPAP), one of the groups of the STAR research unit of the University of Liège, where he benefits from a Marie Curie – COFUND grant. For nearly a year he has been sharing the experience he has acquired, notably at the MSSL-UCL laboratory, in the field of terrestrial auroras and magnetospheric plasma physics, which he now applies to giant planets.
For more than 25 years, the Laboratory for Atmospheric and Planetary Physics (LPAP) has specialized in studying the aurora of Jupiter. The LPAP is actively participating in the NASA-Juno mission, particularly with the UVS spectrograph, a crucial part of which was designed and tested at the Centre Spatial de Liège (CSL) and the JIRAM infrared detector. At the same time, Professor Denis Grodent is leading an international team that is conducting a major Jupiter UV auroras observation campaign with the Hubble Space Telescope. Some of these more recent observations are specifically obtained simultaneously with the XMM-Newton and Chandra telescopes as well as with Juno measurements. The combination of these new results will provide some answers to the many questions raised by the study just published in the journal Nature Astronomy.
The lead author of this article, William Dunn, was visiting the LPAP for a week in October to discuss new discoveries that have been made since the publication of the study.
Pr Denis GRODENT – STAR Research Institute
Laboratory for Atmospheric and Planetary Physics (LPAP)
d.grodent@uliege.be I +32 4 3669773
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