Jupiter's Largest Moons All Have Aurorae That Glow Deep Red And 15x Brighter Than Ours

Thanks in large part to the Juno mission and recent photographs collected by the James Webb Space Telescope, Jupiter is widely known for its stunning aurorae (JWST). Similar to Earth, Jupiter's magnetic field and atmosphere interact with charged solar particles to produce these stunning displays.

Astronomers have also discovered weak aurorae in the atmospheres of Jupiter's biggest moons throughout time (aka. the "Galilean Moons"). They too are the outcome of interaction, in this instance between particles coming from the atmospheres of the moons and Jupiter's magnetic field.

It has always been difficult to find these weak aurorae because sunlight reflected from the moons' surfaces entirely obscures their light fingerprints. NASA helped a team lead by the University of Boston and Caltech observe the Galilean Moons as they moved into Jupiter's shadow for a number of recent studies.

These observations demonstrated the presence of oxygen-aurorae in the atmospheres of Io, Europa, Ganymede, and Callisto. Furthermore, these aurorae are deep red and about 15 times brighter than the common Earthly green patterns.

Astronomers from the Southwest Research Institute (SwRI), the Planetary Science Institute (PSI), the Large Binocular Telescope Observatory (LBT), the Center for Space Physics (CSP) at Boston University, the Division of Geological and Planetary Sciences (GPS) at Caltech, the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, the Earth and Planetary Science at the University of Berkeley, the Laboratory for Atmospheric and Space Physics at the University of Colorado

The two research papers, "The Optical Aurorae of Europa, Ganymede, and Callisto" and "Io's Optical Aurorae in Jupiter's Shadow," were published in the Planetary Science Journal on February 16.

The team's observations incorporated information from the Large Binocular Telescope (LBT), the Apache Point Observatory, and the High-Resolution Echelle Spectrometer (HIRES) at the Keck Observatory (APO).

These observations were timed to prevent interference from sunlight reflected off the surfaces of Io, Europa, Ganymede, and Callisto by seeing them as they entered Jupiter's shadow. This discovery provided crucial details about the moons' atmospheres, which contained oxygen gas (as expected).

According to a Keck Observatory press release, principal author of one of the two articles and professor at Caltech Katherine de Kleer said:

"Because to the moons' near-invisibility in Jupiter's shadow, these observations are challenging. The only proof that we have even positioned the telescope in the appropriate direction is the light coming from their weak aurorae. The brightness of the various auroral hues reveals the likely composition of the atmospheres of these moons. We discover that the major component of the frozen moon atmospheres is likely molecular oxygen, precisely like what we breathe on Earth."

Similar to the Northern and Southern Lights (Aurora Borealis and Australis) on Earth, all four Galilean Moons displayed the same oxygen aurorae.

The oxygen present in the atmospheres of Europa, Ganymede, and Callisto is a result of photolysis, a process in which water ice sublimates and is broken down by solar radiation into its hydrogen gas and oxygen. In the case of Io, sulfur dioxide (emitted by the many volcanoes that dot its surface) interacts with solar radiation to produce sulfur monoxide and elemental oxygen, which is the source of the oxygen.

Yet, because the atmospheres of Europa and Ganymede are significantly thinner, this oxygen glows in infrared wavelengths that are invisible to the human eye.

Salts like sodium chloride and potassium chloride are prevalent in the atmosphere as a result of Io's volcanic activity, where they are also oxidized by sunlight. As a result, the aurorae on Io emanate a sodium-induced yellow-orange light and shine in the infrared (caused by potassium).

This infrared light in the atmospheres of these moons was first noticed by astronomers at this time. Furthermore, despite prior assumptions that water vapor was present in the atmospheres of Europa, Ganymede, and Callisto, the new observations found only very weak evidence of water vapor.

There are rumored to be inner seas beneath the frozen surfaces of all three moons, and there is even some shaky evidence that Europa's atmosphere may contain water vapor brought on by plume activity. These plumes may be linked to the oceanic core of the moon or to liquid reserves within its frozen surface.

The measurements also demonstrated how the aurorae's brightness varies with Jupiter's rotation due to its magnetic field's tilt. As a result of this field's tilt, which is around 10° from Jupiter's axis of rotation as opposed to Earth's 11° tilt, the moons will occasionally interact more with one another.

Last but not least, they observed how the atmospheres changed dramatically in temperature as they moved from being exposed to sunlight to being in Jupiter's shadow. Carl Schmidt, an astronomy professor at Boston University and the second paper's principal author, stated:

"After 15 minutes under Jupiter's shadow, Io's sodium starts to lose a lot of brightness, but it takes many hours for it to regain it. The chemistry of Io's atmosphere can be better understood thanks to these novel properties. It's interesting because eclipses near Jupiter provide a real-world opportunity to study how sunlight affects the atmosphere there."

What was previously a highly intriguing area of inquiry has been made much more exciting by these most recent observations. NASA's Europa Clipper and the ESA's Jupiter ICy moon Explorer are two robotic explorers that space organizations will deploy to Europa and Ganymede in the upcoming years (JUICE).

These missions will fly around these moons several times, collect information about their atmospheres and surfaces, and look for signs of potential life in their innards ("biosignatures"). It will be nothing short of jaw-dropping to see these vivid crimson aurorae up close!

This article was originally published by Universe Today. Read the original article.