Solar storms trigger Jupiter's intense 'Northern Lights' by generating a new X-ray aurora that is eight times brighter than normal and hundreds of times more energetic than Earth's aurora borealis, new research finds. 

It is the first time that Jupiter's X-ray aurora has been studied when a giant storm from the sun has arrived at the planet.

The dramatic findings complement NASA's Juno mission this summer, which aims to understand the relationship between the two biggest structures in the solar system - the region of space controlled by Jupiter's magnetic field (its magnetosphere) and that controlled by the solar wind.

Jupiter's X-ray emission (in magenta and white, for the brightest spot, overlaid on a Hubble Space Telescope optical image) captured by Chandra as a coronal mass ejection (CME) reaches the planet on 2 October 2011, and then after the solar wind subsides on 4 October 2011. The Northern Lights seem to expand southwards and the brightening is clearly visible as the CME arrives. Credit: Credit: Joseph DePasquale, Smithsonian Astrophysical Observatory Chandra X-ray Center.

"There's a constant power struggle between the solar wind and Jupiter's magnetosphere," said William Dunn, a PhD candidate at University College London Mullard Space Science Laboratory and lead author of the new study.

"We want to understand this interaction and what effect it has on the planet," Dunn said. "By studying how the aurora changes, we can discover more about the region of space controlled by Jupiter's magnetic field, and if or how this is influenced by the Sun. Understanding this relationship is important for the countless magnetic objects across the galaxy, including exoplanets, brown dwarfs and neutron stars."

The Sun constantly ejects streams of particles into space in the solar wind. When giant storms erupt, the winds become much stronger and compress Jupiter's magnetosphere, shifting its boundary with the solar wind two million kilometers (1.25 million miles) through space. The new study found that this interaction at the boundary triggers the high energy X-rays in Jupiter's Northern Lights, which cover an area bigger than the surface of the Earth.

The study, published yesterday in the Journal of Geophysical Research - Space Physics, a journal of the American Geophysical Union, comes as NASA's Juno spacecraft nears Jupiter for the start of its mission this summer. Launched in 2011, Juno aims to unlock the secrets of Jupiter's origin, helping us to understand how the solar system, including Earth, formed.

As part of the mission, Juno will investigate Jupiter's relationship with the Sun and the solar wind by studying its magnetic field, magnetosphere and aurora. The research team hopes to find out how the X-rays form by collecting complementary data using the European Space Agency's X-ray space observatory, XMM-Newton, and NASA's Chandra X-ray observatory.

"Comparing new findings from Jupiter with what is already known for Earth will help explain how space weather is driven by the solar wind interacting with Earth's magnetosphere," said Graziella Branduardi-Raymont, an astrophysicist at UCL Mullard Space Science Laboratory and a co-author of the study. "New insights into how Jupiter's atmosphere is influenced by the Sun will help us characterize the atmospheres of exoplanets, giving us clues about whether a planet is likely to support life as we know it."

The researchers tracked the impact of solar storms on Jupiter's aurora by monitoring the X-rays emitted during two 11-hour observations in October 2011 when an interplanetary coronal mass ejection was predicted to reach the planet from the Sun. The scientists used the data collected to build a 3D spherical image to pinpoint the source of the X-ray activity and identify areas to investigate further at different time points.

"In 2000, one of the most surprising findings was a bright 'hot spot' of X-rays in the aurora which rotated with the planet," Dunn said. "It pulsed with bursts of X-rays every 45 minutes, like a planetary lighthouse. When the solar storm arrived in 2011, we saw that the hot spot pulsed more rapidly, brightening every 26 minutes. We're not sure what causes this increase in speed but, because it quickens during the storm, we think the pulsations are also connected to the solar wind, as well as the bright new aurora."

A second study published yesterday in the Journal of Geophysical Research - Space Physics reports that the X-ray aurora responds to quieter 'gusts' of solar wind, deepening this connection between Jupiter and the solar wind.