A glowing arch of red, pink, and white anchors this stunning composite astrophotograph. This is a STEVE (Strong Thermal Emission Velocity Enhancement) caused by a river of fast-moving ions high in the atmosphere. Above the STEVE’s glow, the skies are red; that’s due either to the STEVE or to the heat-related glow of a Stable Auroral Red (SAR) arc. Find even more beautiful astrophotography at the artist’s website and Instagram. (Image credit: L. Leroux-Géré; via APOD)
Tag: planetary science
How Magnetic Fields Shape Core Flows
The Earth’s inner core is a hot, solid iron-rich alloy surrounded by a cooler, liquid outer core. The convection and rotation in this outer core creates our magnetic fields, but those magnetic fields can, in turn, affect the liquid metal flowing inside the Earth. Most of our models for these planetary flows are simplified — dropping this feedback where the flow-induced magnetic field affects the flow.
The simplification used, the Taylor-Proudman theorem, assumes that in a rotating flow, the flow won’t cross certain boundaries. (To see this in action, check out this Taylor column video.) The trouble is, our measurements of the Earth’s actual interior flows don’t obey the theorem. Instead, they show flows crossing that imaginary boundary.
To explore this problem, researchers built a “Little Earth Experiment” that placed a rotating tank (representing the Earth’s inner and outer core) filled with a transparent, magnetically-active fluid inside a giant magnetic. This setup allowed researchers to demonstrate that, in planetary-like flows, the magnetic field can create flow across the Taylor-Proudman boundary. (Image credit: C. Finley et al.; research credit: A. Pothérat et al.; via APS Physics)
The Great Red Spot’s Cycle
First spotted by humanity in 1664, Jupiter‘s Great Red Spot is a seemingly endless storm. Strictly speaking, there is debate as to whether observations prior to 1831 were of the same storm, but there’s no denying that the storm has raged unabated since regular observations began in the first half of the nineteenth century. Despite its longevity, the Great Red Spot is not unchanging. Overall, its major axis is shrinking, making the storm more circular over time. The storm also has a 90-day cycle in which its size, shape, and brightness vary, as seen below. Researchers note that the changes are relatively subtle — at least to the eye — but now that they’ve been identified, it may be possible to use amateur astronomers’ data to track these variations more closely. (Image credits: GRS – K. Gill/NASA, snapshots – A. Simon et al.; research credit: A. Simon et al.; via Gizmodo)
Over a 90 day cycle, Jupiter’s Great Red Spot oscillates in size, shape, and other characteristics. 
Slushy Snow Affects Antarctic Ice Melt
More than a tenth of Antarctica’s ice projects out over the sea; this ice shelf preserves glacial ice that would otherwise fall into the Southern Ocean and raise global sea levels. But austral summers eat away at the ice, leaving meltwater collected in ponds (visible above in bright blue) and in harder-to-spot slush. Researchers taught a machine-learning algorithm to identify slush and ponds in satellite images, then used the algorithm to analyze nine years’ worth of imagery.
The group found that slush makes up about 57% of the overall meltwater. It is also darker than pure snow, absorbing more sunlight and leading to more melting. Many climate models currently neglect slush, and the authors warn that, without it, models will underestimate how much the ice is melting and predict that the ice is more stable than it truly is. (Image credit: Copernicus Sentinel/R. Dell; research credit: R. Dell et al.; via Physics Today)
Underground Convection Thaws Permafrost Faster
In recent years, Arctic permafrost has thawed at a surprisingly fast pace. Much of that is, of course, due to the rapid warming caused by climate change. But some of that phenomenon lives underground, where water’s unusual properties cause convection in gaps between rocks, sediment, and soil.
Water is densest not as ice but as water. This is why ice cubes float in your glass. Water’s densest form is actually a liquid at 4 degrees Celsius. For water-logged Arctic soils, this means that the densest layer is not at the frozen depth but at a higher, shallower depth. This places a dense liquid-infused layer over a lighter one, a recipe for unstable convection.
Illustration of underground convection and permafrost thaw. On the left: temperature and density of the water in Arctic soil varies with depth. The temperature gets colder the deeper you go, but because water is densest at 4 degrees Celsius, the density is greatest at a shallower depth than the freezing interface. As a result of this unstable configuration (dense water over less dense water), convection can occur (right). In a recent numerical simulation, researchers found that this underground convection caused permafrost to thaw much more quickly than it would due to heat conduction alone. In fact, the effects appeared in as little as one month, so in a single summer, this convection could have a big effect on the thaw depth. (Image credit: top – Florence D., figure – M. Magnani et al.; research credit: M. Magnani et al.)
Water Suspected Beneath Mars
The surface features of Mars — crossed by river deltas and sedimentary deposits — indicate a watery past. Where that water went after the planet lost its atmosphere 3 – 4 billion years ago is an open question. But a new study suggests that quite a bit of that water moved underground rather than escaping to space.
The research team analyzed seismic data from the Mars InSight Lander. Marsquakes and meteor strikes on the Red Planet send seismic waves through the planet’s interior. The waves’ speed and other characteristics change as they pass through different materials, and by comparing different waves picked up from the same originating source, scientists can back out what the waves passed through on the way to the detector. In this case, the team concluded that the data best fit a layer of water-filled fractured igneous rock 11.5 – 20 kilometers below the surface. They estimate that the water trapped in this subsurface layer is enough to cover the surface of the planet in a 1 – 2 kilometer deep ocean. (Image credit: NASA/JPL-Caltech; research credit: V. Wright et al.; via Physics World)
An Exoplanet With Earth-Like Temperatures
Although researchers have identified thousands of exoplanets in the last 25 years, most of them are far larger and far hotter than Earth. But a team recently announced the discovery of a temperate neighbor, Gliese 12 b, some 40 light years away. Gliese 12 b is a rocky Venus-sized planet orbiting the cool red dwarf star Gliese 12. Based on the star’s energy output and the planet’s characteristics, the team estimate its equilibrium temperature — about how hot it would be without an atmosphere — as 42 degrees Celsius. (For comparison, Earth’s average surface temperature is 15 degrees Celsius and rising.) The next goal will be to determine whether Gliese 12 b has an atmosphere and, if so, what it’s made up of. (Image credit: NASA/JPL-Caltech/R. Hurt; research credit: S. Dholakia et al.; via Gizmodo)
Junggar Basin Aglow
The low sun angle in this astronaut photo of Junggar Basin shows off the wind- and water-carved landscape. Located in northwestern China, this region is covered in dune fields, appearing along the top and bottom of the image. The uplifted area in the top half of the image is separated by sedimentary layers that lie above the reddish stripe in the center of the photo. Look closely in this middle area, and you’ll find the meandering banks of an ephemeral stream. Then the landscape transitions back into sandy wind-shaped dunes. (Image credit: NASA; via NASA Earth Observatory)
Venusian Lava Flows
Venus is often known as Earth’s twin, given its similar size and proximity. But, thanks to its runaway greenhouse effect, Venus is a hellish landscape buried beneath a hot atmosphere of carbon dioxide and sulfuric acid. Unlike Earth, Venus is not tectonically active, though it does have active volcanoes. A recent study re-examined synthetic aperture radar data from the Magellan spacecraft mission in the early 1990s and found that the data contained evidence of fresh lava flows.
The team found two areas near volcanoes where the surface backscatter changed significantly between orbital observations. After examining many possible explanations for the changes, the team concluded that the differences were most likely due to new lava. They even performed the same analysis for a volcanic field here on Earth between known lava flows and observed the same behavior. Combined with another recent study that found evidence of volcanic activity in Magellan data, signs are pointing toward Venus being about as volcanically active as our own planet, even if the mechanisms driving the volcanism differ. (Image credit: NASA/JPL-Caltech; research credit: D. Sulcanese et al.; via Gizmodo)
Rocky Exoplanet With an Atmosphere
In the past few decades, the number of exoplanets we’ve found has ballooned to over 5,000, but most of these worlds are gas giants closer to Jupiter than our rocky Earth. But a recent study has turned up evidence of a rocky exoplanet that, like Earth, has an atmosphere made up of more than hydrogen.
By combining observations from the JWST with those from other telescopes, the team found that 55 Cancri e — an exoplanet nearly 9 times more massive than Earth in a system about 41 light years from us — probably has an atmosphere made up of carbon dioxide or carbon monoxide. 55 Cancri e is still a planet extremely unlike our own, though; it’s tidally locked to its star so that one side always faces the star, and its equilibrium temperature is an estimated 2000 Kelvin. That’s actually a lower temperature than expected, indicating that an atmosphere is helping distribute heat around the planet. Based on the JWST measurements, the researchers suggest that the planet’s volatile atmosphere could be supported by outgassing from a magma ocean. (Image credit: NASA/ESA/CSA/R. Crawford; research credit: R. Hu et al.; via Gizmodo)
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