Skip to main content

Aurorae light up the skies over Jupiter’s four largest moons

One of the Earth’s great natural wonders is the Northern Lights or aurora borealis; delicate waves of colors that appear in the sky over polar regions when energetic particles from the sun interact with Earth’s magnetic field. But Earth isn’t the only planet to experience aurorae, as the strong magnetic fields of planets like Jupiter and Saturn mean that aurorae are observed there as well.

Aurorae aren’t just limited to Jupiter though but are also present on four of its moons: Io, Europa, Ganymede, and Callisto. Astronomers recently used the High-Resolution Echelle Spectrometer (HIRES) instrument at the W. M. Keck Observatory in Hawai’i to observe the moons while they were in the shadow of Jupiter, allowing them to see the faint aurorae.

Artist’s rendition of oxygen, sodium, and potassium aurorae as Io enters Jupiter’s shadow.
Artist’s rendition of oxygen, sodium, and potassium aurorae as Io enters Jupiter’s shadow. Chris Faust

“These observations are tricky because in Jupiter’s shadow, the moons are nearly invisible,” said one of the lead researchers, Katherine de Kleer of Caltech, in a statement. “The light emitted by their faint aurorae is the only confirmation that we’ve even pointed the telescope at the right place.”

Different colors of aurorae are created by different elements, and the researchers were able to see some green aurorae created by oxygen similar to those we see on Earth. But at low concentrations, oxygen produces a red aurora, and as these moons have extremely thin atmospheres they show aurorae that are 15 times more red than green.

And on Io, which has plumes of sodium chloride and potassium chloride coming from its volcanoes, its aurorae can have a yellow-orange color.

“The brightness of the different colors of aurora tell us what these moons’ atmospheres are likely made up of,” said de Kleer. “We find that molecular oxygen, just like what we breathe here on Earth, is likely the main constituent of the icy moon atmospheres.”

As aurorae occur when particles from the sun interact with a magnetosphere, you might expect that a moon would need a magnetic field of its own to experience these phenomena. But three of the moons in question — other than Ganymede — don’t have their own magnetic fields. However, the magnetic field of Jupiter is so strong that its effects reach out to its moons.

The magnetic field of Jupiter is also titled, so the field on the moons varies as the planet rotates, and that means their aurorae change in brightness over time.

Another change that can happen to the aurorae is when the atmospheres warm or cool as they exit or enter the shadow of Jupiter, an effect which was seen on Io.

“Io’s sodium becomes very faint within 15 minutes of entering Jupiter’s shadow, but it takes several hours to recover after it emerges into sunlight,” said another of the lead researchers, Carl Schmidt of Boston University. “These new characteristics are really insightful for understanding Io’s atmospheric chemistry. It’s neat that eclipses by Jupiter offer a natural experiment to learn how sunlight affects its atmosphere.”

The research is published in two papers in The Planetary Science Journal.

Editors' Recommendations

Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
Stunning space station video shows glorious aurora over Earth
An aurora as viewed from the ISS.

NASA has released a breathtaking time-lapse video showing a recent aurora over Earth.

The footage was captured by a camera on the International Space Station (ISS), which orbits our planet at an altitude of around 250 miles. Besides the Earth and the gorgeous green aurora, it also shows several of the station’s solar panels moving slowly to capture the sun's rays.

Read more
Juice spacecraft heading to spaceport ahead of mission to study Jupiter’s moons
The European Space Agency's Juice spacecraft will explore Jupiter's icy moons.

Out solar system will soon be getting a new explorer, as a mission to study the moons of Jupiter readies for launch.

The European Space Agency's Jupiter Icy Moons Explorer mission, or JUICE, is scheduled for launch in just a few months' time, so the spacecraft is now being packed up at its testing location in Toulouse, France, for transport to its launch location in French Guiana.

Read more
Light pollution is cutting off views of the night sky for many
A startling analysis from Globe at Night — a citizen science program run by NSF’s NOIRLab — concludes that stars are disappearing from human sight at an astonishing rate. The study finds that, to human eyes, artificial lighting has dulled the night sky more rapidly than indicated by satellite measurements. The study showcases the unique contributions that citizen scientists can make in essential fields of research. This graphic illustrates how the greater the amount of light pollution, and therefore skyglow, the fewer the stars that are visible. The numeric scale is similar to the one used by Globe at Night participants. 

If you have even a passing interest in astronomy, odds are good that you've considered the problem of light pollution. As there are more and more sources of bright light at night on Earth, it makes it harder and harder to see the stars in the sky. But recent analysis has pointed out that the problem could be worse than anticipated, as what is visible to the human eye is even less than satellite measurements have indicated.

According to the National Science Foundation's NOIRLab, around 30% of the global population and 80% of the U.S. population can no longer see our galaxy, the Milky Way. And the new research shows that the problem is getting worse.

Read more