Our planet is constantly carved by the flow of wind, water, and ice. These images, all shortlisted by the International Aerial Photographer of the Year competition, highlight those forces. From meandering rivers and spreading deltas to cracked valleys and windswept dunes, flow is all around us. (Image credit: Various Artists/IAPOTY, see images for details; via Colossal)
Mars was once a warmer, wetter place, swathed in a thick and protective atmosphere. Unlike Earth, Mars lacks a strong global magnetic field, which allows the solar wind to strip its atmosphere, but the exact mechanisms of that process have been unclear. But a new study has caught the process in action.
By combining simultaneous measurements from two spacecraft–NASA’s MAVEN and China’s Tianwen-1–the team was able to monitor the upstream solar wind conditions and the atmospheric ions escaping. They found that previously-observed “plasma clouds” in the Martian atmosphere result from a Kelvin-Helmholtz instability between the solar wind and Mars’ electric field. Within these clouds, the ion flux is ten to a hundred times greater than at steady-state conditions.
This mechanism directly couples ion escape from Mars’ atmosphere to the solar wind, and it’s likely that this process plays out for other unmagnetized planets as well. (Image credit: Mars – NASA, illustration – C. Zhang et al.; research credit: C. Zhang et al.; via Gizmodo)
Photographer Barbara Brown captured these striking aerial views in Namibia. Coastal dunes and saltworks feature in the photos from Walvis Bay, where wind, waves, evaporation, and humankind have shaped the landscape. The colorful and dendritic dune images come from Sossusvlei, where the ephemeral Tsauchab River ends in the Namib Desert. Recent flooding left its mark on the dry landscape. (Image credit: B. Brown/IAPOTY; via Colossal)
Uranus and Neptune–known as our system’s ice giants–are our least explored planets. Both have received exactly one flyby, from the Voyager 2 spacecraft. The data from those flybys remain our primary source of knowledge about each planet. The traditional model for each planet’s interior (dating back to before the flybys) consists of three layers: a rocky core; an icy mantle made up of water, ammonia, and methane; and a hydrogen/helium-rich atmosphere. That structure is one way to match the limited measurements we have from these planets, but, as today’s preprint study points out, it’s not the only way.
The authors suggest an alternative structure, in which a hydrogen-rich atmosphere overlays a supercritical magma ocean capable of dissolving hydrogen into heavier, metallic elements. Their suggestion is motivated by several factors. First, objects in the outer solar system–including Kuiper Belt objects–have less icy material than originally assumed, which suggests that Uranus and Neptune’s progenitors wouldn’t have been so ice-rich, either. Second, our understanding of how “rocky” materials respond at the temperatures and pressures found in these planet interiors has evolved. In particular, silicate, hydrogen, and iron are actually miscible at these conditions. That means that discrete sub-layers separated by material type are not as likely.
Using the magma ocean model, the team found compositions for both Uranus and Neptune that conformed well to our limited data about their gravitational and magnetic field properties. Time–and more data–will tell as to which interior model best describes these enigmatic giants. (Image credit: NASA; research credit: E. Young et al. (preprint); via Gizmodo)
In the past few decades, our knowledge of exoplanets has exploded, but we’re still relatively limited in what we can learn about these worlds. That’s due, in large part, to the indirect way we observe them. Most exoplanets are found when we see them transit, passing between Earth and their star. During a transit, the planet blocks a portion of the light we would otherwise detect from the star, letting us know that something’s there. We’re often able to measure the spectra of light passing through the exoplanet’s atmosphere, giving us a glimpse of chemical signatures.
Today’s study looks at exoplanet WASP-94A b, a gas giant tidally-locked so that only one side ever faces its star. In its transit, researchers could clearly measure different spectra from the morning and evening sides of the planet. The asymmetry seems to indicate that the exoplanet develops thick clouds on the nightside, which then dissipate during the daytime. (Image credit: H. Robbins/JHU; research credit: S. Mukherjee et al.; via Nature)
On Earth, most waves form when wind blows across the water. The shear and added energy from the wind ripples the surface, eventually building up waves (through the Kelvin-Helmholtz instability). The same process should happen anywhere else where wind and open liquid surfaces meet–even on other planets. To explore this, researchers built a new model, PlanetWaves, that predicts the waves based on a planet’s gravity, atmospheric conditions, and the density, viscosity, and surface tension of its surface liquid.
After validating the model with conditions on Earth, the team explored wave conditions for Titan, ancient Mars, and several exoplanets. They found that Titan’s lighter gravity and liquid ethane (which is less dense than water) combined to make waves on Titan much taller than those generated at the same wind speed on Earth (top image). You can watch them in action in the video below. Standing in a light breeze on Titan, you’d watch giant 3-meter waves rolling in.
The team also found that waves on Mars would have gotten shorter as Mars lost its atmosphere and the air pressure dropped. Over time, the same wind speed would have elicited smaller and smaller waves. Wave action has a big effect on a landscape’s erosion, so understanding how waves look on other planets will help us parse their geography. (Video, image, and research credit: U. Schneck et al.; via MIT News; submitted by Joseph S.)
In planetary atmospheres, energy and vorticity can cascade from large scales to smaller ones, but the mechanics of this transfer remain somewhat elusive. In a recent experiment, researchers built a lab-scale representation of an atmosphere using a meter-scale rotating annular tank. The outer bottom edge of the tank gets heated–representing the sun’s warming at the equator–while a pipe in the center of the tank gets cooled near the tank surface, which mimics the chilling effect of the poles. Researchers filled the tank with a water-glycerol mixture and recorded how their artificial atmosphere responded at different rotation rates.
The results show an energy spectrum that’s consistent with atmospheric observations–with a steep drop at large length scales and a flatter one at smaller scales. But interestingly, they also found that the cascade was temperature-dependent in ways that current models don’t predict. Untangling that effect could help us understand not only our atmosphere but those of other planets. (Image credit: tank – H. Scolan, animation – S. Ding et al.; research credit: S. Ding et al.; via APS)
Uranus is one of our solar system’s oddest inhabitants, stuck spinning on its side with a tilted and offset magnetosphere. To better understand it, a team observed the planet for 17 hours with JWST. The near-infrared measurements gave new insight into the planet’s ionosphere, where auroras form. They found that temperatures peaked between 3,000 and 4,000 kilometers, while ion densities peaked at 1,000 kilometers. They also confirmed previous observations that Uranus’s upper atmosphere is cooling down. (Image and video credit: ESA/Webb/NASA/CSA/STScI/P. Tiranti/H. Melin/M. Zamani; research credit: P. Tiranti et al.; via Gizmodo)
On the outskirts of our solar system, two enigmatic giants loom: Uranus and Neptune. In terms of mass and size, both resemble many of the exoplanets discovered in recent years. Within our own solar system, these planets are known as “icy giants,” but a new study suggests that moniker may be wrong.
Pinning down the interior composition of a planet is tough on limited measurements. In the case of these outer planets, our main data is gravitational, recorded from visiting spacecraft. That information cannot tell us directly what the composition of a planet is, but it gives constraints for what materials could produce such a gravitational field.
In their simulation, researchers began with random interior configurations for Uranus and Neptune, then had the model iterate through configurations to simultaneously match the gravitational measurements while satisfying the thermodynamic and physical constraints of a stable planet. By repeating the process several times, the researchers created a catalog of potential interiors for Uranus and Neptune. And while some were water-rich–consistent with the “icy giant” title–others were remarkably rocky.
The team suggests that we may need to retire that moniker and consider the possibility that these worlds are more like our own than we thought. To find out which is true, we will need more spacecraft to visit our frigid neighbors, to provide new gravitational measurements and other observations. (Image credit: NASA/ESA/A. Simon/M. Wong/A. Hsu; research credit: R. Morf and L. Helled; via Physics World)
The vivid bands of a gas giant like Jupiter come from the planet’s combination of rotation and convection. It’s possible to create the same effect in a lab by rapidly spinning a tank of water around a central ice core. That’s the physical set-up behind this research poster–note the illustration in the lower right corner. The central snapshots show how temperature gradients on the water surface change the faster the tank rotates. At higher rotational speeds, the parabolic water surface gets ever steeper and Jupiter-like temperature bands form. (Image credit: C. David et al.)
