Scientists have detected a powerful X-ray aurora hotspot near Jupiter's south pole and it does not behave how they expected.
Rather than pulsing in sync with the northern aurora, the southern hotspot runs to its own regular beat.
"The south has this really strange regular pulsation every 11 minutes," said William Dunn, an astronomer at University College London and lead author of the study, published in Nature Astronomy.
This behaviour, he explained, is different to aurora on Earth, where the northern and southern lights are both irregular and generally mirror each other.
"If you think of the [spots] as these twin features then maybe you expect them to be identical and behaving in time with each other and they are not doing that at all," Dr Dunn said.
The discovery adds to the mystery of how Jupiter's powerful auroras are created — a puzzle scientists hope will be solved by NASA's Juno spacecraft, currently orbiting the planet.
On Earth, an aurora is created when the solar wind — a stream of charged particles from the Sun — rains down on the planet's magnetic field. The lines of that field direct the particles to the poles, where they collide with gas atoms and emit light.
But while Earth's auroras only appear during solar storms, Jupiter's are permanent.
These powerful displays are generated by high-energy particles in the atmosphere of Jupiter and its moons, interacting with the planet's own magnetic field.
"These [particles] are accelerated in magnetic fields and slammed onto the high atmospheric layers in the polar regions of the planet," said Dr Kedziora-Chudczer, who also studies Jupiter.
One question puzzling scientists is whether, and to what degree, the solar wind also plays a role powering Jupiter's aurora.
In 2000, astronomers discovered an aurora hotspot spewing out X-rays at the planet's north pole.
Recent research by Dr Dunn and colleagues found brightening of this hotspot during a solar storm, which suggested the solar wind was indeed involved.
But auroras at the planet's south pole are much harder to see from Earth.
On these days, not only was Jupiter's south pole tilted towards the two observatories orbiting Earth, but the northern hotspot was also visible.
The team then compared the activity of the southern and northern hotspots — both of which cover an area greater than the surface of the Earth.
While the southern aurora gave off pulses like clockwork, pulses from the from the northern spot were less predictable.
"Sometimes it pulses at 45 minutes, sometimes it pulses at 12 minutes, and sometimes it pulses erratically," said Dr Dunn.
The researchers also saw the intensity of the two auroras increase and decrease at different times.
Dr Dunn said the regular pulse his team detected at the south pole may be caused by the solar wind hitting a specific part of the planet's magnetic field, causing it to vibrate and send waves towards the south pole every 11 minutes.
The charged particles can then surf these waves and collide with the atmosphere of the planet to produce the bright X-ray aurora.
"It is weird because the aurora are like the signature of the magnetic field. Whatever is happening on a magnetic field line should trigger things that happen in both poles."
Dr Dunn said it's possible that because we don't get as good a view of the southern hemisphere, we may only be seeing some of the lines that are vibrating.
But, he said, there is mounting evidence from other observations that show the two auroras are acting independently of each other.
Juno is tasked with measuring Jupiter's magnetosphere for the first time.
"Juno is essentially rewriting much of what we had previously thought we knew about the planet, just as these X-ray observations contradict what we thought we knew about the aurora," said Dr Dunn.
Dr Kedziora-Chudczer agreed that local effects in Jupiter's magnetosphere could cause the aurora to behave independently, but said more observations were needed to confirm these results.
"Observations of auroral emissions in all wavelengths, together with measurement of particle fluxes in situ by spacecraft like Juno, will give us a complete picture of these interactions."
Rather than pulsing in sync with the northern aurora, the southern hotspot runs to its own regular beat.
"The south has this really strange regular pulsation every 11 minutes," said William Dunn, an astronomer at University College London and lead author of the study, published in Nature Astronomy.
This behaviour, he explained, is different to aurora on Earth, where the northern and southern lights are both irregular and generally mirror each other.
"If you think of the [spots] as these twin features then maybe you expect them to be identical and behaving in time with each other and they are not doing that at all," Dr Dunn said.
The discovery adds to the mystery of how Jupiter's powerful auroras are created — a puzzle scientists hope will be solved by NASA's Juno spacecraft, currently orbiting the planet.
Jupiter's auroras not like other planets
Jupiter has the most powerful auroras in the solar system, but they are very different to those on other planets such as Earth, said astronomer Lucyna Kedziora-Chudczer of the University of New South Wales.On Earth, an aurora is created when the solar wind — a stream of charged particles from the Sun — rains down on the planet's magnetic field. The lines of that field direct the particles to the poles, where they collide with gas atoms and emit light.
But while Earth's auroras only appear during solar storms, Jupiter's are permanent.
These powerful displays are generated by high-energy particles in the atmosphere of Jupiter and its moons, interacting with the planet's own magnetic field.
"These [particles] are accelerated in magnetic fields and slammed onto the high atmospheric layers in the polar regions of the planet," said Dr Kedziora-Chudczer, who also studies Jupiter.
One question puzzling scientists is whether, and to what degree, the solar wind also plays a role powering Jupiter's aurora.
In 2000, astronomers discovered an aurora hotspot spewing out X-rays at the planet's north pole.
Recent research by Dr Dunn and colleagues found brightening of this hotspot during a solar storm, which suggested the solar wind was indeed involved.
But auroras at the planet's south pole are much harder to see from Earth.
Spotting the southern X-ray hotspot
To find the southern aurora hotspot, Dr Dunn and his international team analysed data collected by two X-ray space telescopes on two separate occasions, 10 years apart, in 2007 and 2016.On these days, not only was Jupiter's south pole tilted towards the two observatories orbiting Earth, but the northern hotspot was also visible.
The team then compared the activity of the southern and northern hotspots — both of which cover an area greater than the surface of the Earth.
While the southern aurora gave off pulses like clockwork, pulses from the from the northern spot were less predictable.
"Sometimes it pulses at 45 minutes, sometimes it pulses at 12 minutes, and sometimes it pulses erratically," said Dr Dunn.
The researchers also saw the intensity of the two auroras increase and decrease at different times.
Dr Dunn said the regular pulse his team detected at the south pole may be caused by the solar wind hitting a specific part of the planet's magnetic field, causing it to vibrate and send waves towards the south pole every 11 minutes.
The charged particles can then surf these waves and collide with the atmosphere of the planet to produce the bright X-ray aurora.
"It is weird because the aurora are like the signature of the magnetic field. Whatever is happening on a magnetic field line should trigger things that happen in both poles."
Dr Dunn said it's possible that because we don't get as good a view of the southern hemisphere, we may only be seeing some of the lines that are vibrating.
But, he said, there is mounting evidence from other observations that show the two auroras are acting independently of each other.
Juno spacecraft may solve aurora mystery
Dr Dunn said the next step in solving the mystery of Jupiter's auroras was to compare polar observations taken by the X-ray observatories with ultraviolet and infrared data from NASA's Juno spacecraft, which is flying directly over the poles every 53 days.Juno is tasked with measuring Jupiter's magnetosphere for the first time.
"Juno is essentially rewriting much of what we had previously thought we knew about the planet, just as these X-ray observations contradict what we thought we knew about the aurora," said Dr Dunn.
Dr Kedziora-Chudczer agreed that local effects in Jupiter's magnetosphere could cause the aurora to behave independently, but said more observations were needed to confirm these results.
"Observations of auroral emissions in all wavelengths, together with measurement of particle fluxes in situ by spacecraft like Juno, will give us a complete picture of these interactions."
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