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.
