Though we rarely notice it, our sky is always aglow. Washed in solar radiation, the oxygen and nitrogen molecules at high altitude get broken apart during the daytime and recombine at night, producing a luminescent glow that forms a uniform backdrop against the sky. In this image, the airglow forms a bull’s-eye-like set of rings, thanks to atmospheric gravity waves left behind by a thunderstorm. (Image credit: J. Dai; via APOD)
Tag: planetary science
Listen to a Martian Dust Devil
A lucky encounter led the Perseverance rover to record the first-ever sound of a dust devil on Mars. The rover happened to have its microphone on (something that only happens a few minutes every month) just as a dust devil swept directly over the rover. Check out the video above to see and hear what Perseverance captured.
Using the rover’s instrumentation, researchers worked out that the dust devil was at least 118 meters tall and about 25 meters wide. The team was even able to determine the density of dust in the vortex from the sound of individual grain impacts captured in the acoustic signal! Serendipitous as the experience was, planetary scientists may now look to include microphones on more missions, since we now know how to get useful meteorological data from them. (Video credit: JPL-Caltech/NASA; image credit: LPL/NASA; research credit: N. Murdoch et al.; via AGU Eos; submitted by Kam-Yung Soh)
Snowing in the Core
Some rocky planetary bodies, like Jupiter‘s moon Ganymede, generate magnetic fields through snow-like, solid precipitation that falls in their liquid metal cores. To study this peculiar and complex arrangement, researchers look at sugar grains falling through — and dissolving into — water. The solid sugar grains mimic the iron snowflakes that fall in Ganymede’s core. As they sink, they drag fluid with them. But the grains can also dissolve, making the fluid around them denser and prone to sinking even faster. The dense, sinking flows trigger buoyant convection inside the surrounding fluid.
As seen in the experiments, there are many factors competing here. Large grains dissolve more slowly and are able to drag more fluid with them as they fall. Small grains, on the other hand, dissolve quickly, causing more buoyancy-driven flows. Laboratory analogs like these help scientists unravel the complexities of situations we cannot observe otherwise. (Image and video credit: Q. Kriaa et al.)
Stabilizing Jupiter’s Polar Storms
Four years ago, Juno discovered an octagon of eight cyclones at Jupiter’s northern pole and a similar five cyclone structure at its southern pole. Since then, both polygons have remained intact. What keeps the storm systems so stable is still an open question, but a recent observational study using Juno measurements found that an anticyclonic ring sits between the central and outer cyclones. In line with a previous theoretical study, this ring structure helps shield and stabilize the storm system.
The underlying convective mechanisms of the storm remain a mystery, though, as the current study is limited in resolution to a scale of about 200 kilometers. (Image credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM; research credit: A. Ingersoll et al.; via Gizmodo)
Martian Glaciers
On Earth, glaciers slide on lubricating layers of water, leaving complex landscapes like fjords and drumlins in their wake. Mars — though once home to enormous ice masses — lacks those geological features. Scientists assumed, therefore, that Martian ice stayed frozen and unmoving. But a new study demonstrates that is not the case.
Researchers used computational modeling to simulate two identical glaciers: one under Earth-like conditions and one under the lower gravity of Mars. They found that Martian glaciers did indeed move, but Mars’s lower gravity, combined with better water drainage beneath the ice, meant that they moved exceedingly slowly. Martian glaciers did erode the landscape but into different features than on Earth. Instead of forming moraines and drumlins, a large Martian glacier would instead carve channels and eskar ridges, geological features found on Mars today. (Image credit: NASA/JPL-CalTech/Uni. of Arizona; research credit: A. Grau Galofre et al.; via AGU; submitted by Kam-Yung Soh)
Jupiter’s Frosted Clouds
This 3D rendering of Jupiter’s cloud tops is based on flyby data from the JunoCam instrument. It’s not a true physical image of the cloud tops, though scientists are working on a calibration for that. Instead, the elevations shown here are based on the intensity of visible light registered by the instrument. This measure correlates with cloud height, but there are exceptions. New 3D renderings of Jovian clouds show textured swirls akin to a cupcake’s sculpted frosting. The images are based on flyby data from the JunoCam instrument. Because illumination of the clouds is generally brightest for the highest clouds, the team has rendered elevation based on brightest. While this is somewhat physical, it’s not exactly what Jupiter looks like. For that, Juno scientists are working on a calibration that will translate these initial renderings into a truer physical model. Nevertheless, the results are stunning, especially the flyover video embedded over here! (Image credit: 3D renders – NASA / JPL-Caltech / SwRI / MSSS / G. Eichstädt, image pair – G. Eichstädt et al.; via phys.org; submitted by Kam-Yung Soh)
Cross your eyes to see this image pair as a 3D image of Jupiter’s cloud tops. The brighter regions will appear closer than the darker ones. 
Predicting Alien Ice
Europa is an ocean world trapped beneath an ice shell tens of kilometers thick. To better understand what we might find in those oceans, researchers turn to analogs here on Earth, looking at Antarctica’s ice shelves. Beneath those shelves, ice forms via two mechanisms: the first, congelation ice, freezes directly onto the existing ice-water interface. The second, frazil ice, forms crystals in supercooled water columns, which drift upward in buoyant currents and settle on the ice shelf like upside-down snow (pictured above).
Based on Europa’s conditions, the researchers conclude that congelation ice would gradually thicken the ice shell as the moon’s interior cools. But in areas where the shell is thinned by local rifts and Jovian tidal forces, frazil ice is likely to form. (Image credit: H. Glazer; research credit: N. Wolfenbarger et al.; via Physics World)
Neptune’s Seasonal Changes
Ice giant Neptune orbits our sun once every 165 years, meaning that each season on the planet lasts about 41 years here on Earth. Currently, the side of Neptune facing us is entering early summer, but a recent survey of atmospheric measurements show that Neptune’s stratosphere is experiencing some unexpected changes. Between 2003 and 2018, the team found that global stratospheric temperatures actually decreased by 8 degrees Celsius. Even more dramatically, Neptune’s southern pole warmed by a full 11 degrees Celsius between 2018 and 2020. Both results hint that atmospheric patterns on the planet may be far more complex than current models assume. (Image credit: NASA/JPL; research credit: M. Roman et al.; via Physics World)
Extreme Weather
Many of the exoplanets we’ve observed so far are extreme environments. WASP-121b is known as a hot Jupiter, a gas giant so close to its star that it orbits in just 30 hours. The exoplanet is tidally-locked to its star, meaning that one side always faces toward the star and the other faces away. This constant sunlight makes the daytime side of the planet hot enough to vaporize metals. A recent study combined observations of the exoplanet with numerical simulations to model both the daytime and nighttime atmosphere of the exoplanet. The results are pretty wild. The authors found evidence of 18,000 km/h winds that blow hot gases from the dayside to the nightside, where temperatures cool enough for some metals — primarily corundum — to rain out of the atmosphere. Given the trace amounts of other elements available in the atmosphere, the authors posit that the nightside of the planet may have rainfall of liquid rubies and sapphires. (Image credit: NASA/ESA; research credit: T. Mikal-Evans et al.; via Physics World)
Martian Flyover
Fly over a Martian crater in this incredibly detailed 8K video built from Mars Reconnaissance Orbiter imagery. Like Earth’s deserts, Mars is largely shaped by wind, and we get some fantastic views of sand ripples in this flyover. For reference, the vertical scale covered in the video image is roughly 1 kilometer. It’s pretty astounding to see this kind of detail from a spacecraft 250 kilometers away! (Video and image credit: S. Doran/NASA; via Colossal)
