Jupiter is known for its spectacular auroras, thanks in no small part to the Juno orbiter and recent images taken by the James Webb Space Telescope (JWST). Like Earth, these dazzling displays are the result of charged solar particles interacting with Jupiter’s magnetic field and atmosphere.
Over the years, astronomers have also discovered faint auroras in the atmospheres of Jupiter’s largest moons (aka. the “Galilean moons”). These are also the result of interaction, in this case, between Jupiter’s magnetic field and particles coming from the moon’s atmosphere.
Detecting these faint auroras has always been a challenge because sunlight reflected off the moon’s surface completely washes out their light signatures. In a series of recent papers, a team led by the University of Boston and Caltech (with support from NASA) observed the Galilean moons as they passed into Jupiter’s shadow.
These observations revealed that Io, Europa, Ganymede, and Callisto all experience oxygen aurorae in their atmospheres. Moreover, these auroras are deep red and almost 15 times brighter than the familiar green patterns we see on Earth.
The research team included astronomers from 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, Earth and Planetary Sciences at UC Berkeley, Large Binocular Telescope Observatory (LBT), Southwest Research Institute (SwRI), Planetary Science Institute (PSI), Leibniz-Institute for Astrophysics Potsdam (AIP) and NASA’s Goddard Space Flight Center.
The two studies, titled “The Optical Aurorae of Europa, Ganymede and Callisto” and “Io’s Optical Aurorae in Jupiter’s Shadow,” appeared Feb. 16 in Planetary Science Journal.
The team’s observations combined data from the Keck Observatory’s High-Resolution Echelle Spectrometer (HIRES) with high-resolution spectra from the Large Binocular Telescope (LBT) and the Apache Point Observatory (APO).
These observations were timed to see Io, Europa, Ganymede and Callisto as they entered Jupiter’s shadow to avoid interference from sunlight reflecting off their surfaces. These data revealed valuable information about the composition of the moon’s atmosphere, which included oxygen gas (as expected).
Katherine de Kleer, a Caltech professor and lead author of one of two papers, explained in a Keck Observatory press release:
“These observations are difficult because in Jupiter’s shadow the moons are almost invisible. The light emitted by their faint auroras is the only confirmation that we have even pointed the telescope in the right place. The brightness of the different colors of the auroras tell us what these lunar atmospheres are probably made up of. We find that molecular oxygen, just like what we breathe here on Earth, is probably the main component of the icy lunar atmospheres.”
All four Galilean moons displayed the same oxygen auroras, similar to what we see with the Aurora Borealis and Australis (northern and southern lights) here on Earth.
In the case of Europa, Ganymede and Callisto, the oxygen content in the atmosphere is due to photolysis, a process in which water ice sublimates and is broken down by solar radiation into hydrogen gas and oxygen. In Io’s case, the oxygen is caused by sulfur dioxide (spewed from the many volcanoes that litter the surface) interacting with solar radiation to form sulfur monoxide and elemental oxygen.
But because of their much thinner atmospheres, this oxygen glows in deep red and (for Europa and Ganymede) in infrared wavelengths—the latter undetectable to the human eye.
Due to Io’s volcanic activity, salts such as sodium chloride and potassium chloride are also present in the atmosphere, where they are also broken down by solar radiation. This causes the auroras on Io to emit a yellow-orange glow (caused by sodium) and glow in the infrared (caused by potassium).
This was the first time astronomers observed this infrared glow in these moons’ atmospheres. Moreover, the new measurements also revealed minimal evidence of water vapor, which was previously thought to be a component of the atmospheres of Europa, Ganymede and Callisto.
All three moons are theorized to have internal oceans beneath their icy surfaces, and there is even some preliminary evidence that water vapor in Europa’s atmosphere may be the result of plume activity. These clouds are thought to be connected to the moon’s internal ocean or liquid reservoirs within the icy shell.
The observations also showed how Jupiter’s tilted magnetic field causes the aurora borealis to vary in brightness as the gas giant rotates. The inclination of this field, about 10° from Jupiter’s axis of rotation compared to Earth’s 11° inclination, means that the moons will experience greater interaction at certain times in their orbits.
Finally, they also noted how the atmospheres responded quickly to temperature changes caused by the transition between exposure to sunlight and passage within Jupiter’s shadow. Said Carl Schmidt, professor of astronomy at Boston University and lead author of the second paper:
“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. These new properties are really insightful for understanding Io’s atmospheric chemistry. It’s nice that eclipses of Jupiter offer a natural experiment for learning how sunlight affects the atmosphere.”
These latest observations have added excitement to what is already a very exciting field of research. In the coming years, space agencies will send several robotic explorers to Europa and Ganymede – NASA’s Europa Clipper and ESA’s JUpiter ICy moon Explorer (JUICE).
These missions will conduct multiple flybys of these moons, collect data on the composition of their atmospheres and surfaces, and attempt to detect indications of possible life in their interiors (“biosignatures”). Seeing these bright red northern lights up close will be nothing short of shocking!
This article was originally published by Universe Today. Read the original article.