FYFD

Tag: planetary science

  • 2D Turbulence

    2D Turbulence

    Turbulence, the chaotic regime of fluid dynamics, is a complicated beast. It’s hard to analyze or predict, but we do understand some general ideas about it, like the fact that energy starts out in large eddies, cascades down smaller and smaller ones, and finally gets dissipated at the smallest scales, where viscosity snuffs them out. But that’s only true in three dimensions.

    Two-dimensional turbulence – what you get when you confine your fluid to a flat plane – is even weirder. When turbulence is flat, you can actually get an inverse energy cascade, where the energy of small eddies can add up to feed bigger ones. For awhile, this was treated as a mathematical curiosity; after all, we live in a three-dimensional world. But there are situations in life that are nearly two-dimensional, like the surface of a soap bubble or the atmosphere of a planet (which is typically exceptionally thin compared to the planet’s radius). And, little by little, scientists are collecting evidence that this inverse cascade – a flow of energy from small scales to larger ones – does actually happen in the real world. Understanding how this works may explain why hurricanes can intensify even when conditions are “wrong” and how Jupiter’s Great Red Spot has persisted for centuries. To learn more, check out Quanta Magazine’s full article on the work. (Image credit: NASA et al., M. Appel; via Quanta; submitted by Kam-Yung Soh)

  • Dust Envelopes Mars

    Dust Envelopes Mars

    Day has turned into night for NASA’s Opportunity rover as a massive dust storm envelopes Mars. The first signs of the dust storm were reported May 30th, and over the last two weeks, the storm has grown to an area larger than North America and Russia combined. Despite the low pressure and density of Mars’ atmosphere, solar heating can create fairly strong winds – they don’t reach hurricane-force speeds, but they’d qualify as a very windy day here on Earth. With the lower gravity on Mars, this can lift dust well into the atmosphere, choking out the sunlight Opportunity needs to continue operating. The rover has entered a low-power mode and is no longer responding to communications. Martian dust storms have been known to last for weeks or even months, and this may be the last we hear from the intrepid rover on its fifteen year journey. Here’s hoping that Opportunity makes it through the storm and can eventually get the solar power needed to phone home again. (Image credit: NASA JPL)

  • Jupiter’s Swirls

    Jupiter’s Swirls

    Sometimes it amazes me that the Juno spacecraft was originally designed without any cameras onboard. The JunoCam instrument has produced stunning imagery of Jupiter thus far and shows no signs of stopping soon. The latest wonder is this false-color, high-contrast animation showing the motion of Jupiter’s clouds swirling and flowing past one another. 

    Now, this is not Jupiter as you would see it by eye. This animation is derived from two images taken 8 minutes and 41 seconds apart. In that time, Juno  covered a lot of distance, so the two images had to be mathematically re-projected so that they appeared to be taken from the same location. Then, by comparing relative positions of recognizable features in the two photos and applying some understanding of fluid mechanics, observers could calculate the probable flow between those two states. Although this is a coarse example, it’s the same kind of technique often used in fluid dynamical experiments when measuring how flows change between two images. (Image credit: NASA/JPL/SwRI/MSSS/G. Eichstädt, source; via EuroPlanet; submitted by Kam-Yung Soh)

  • Colorful Erosion

    Colorful Erosion

    Wind, water, and gravity are great sculptors of our world. This false-color satellite image shows the Ga’ara Depression in Iraq, which formed some 300 million years ago beneath a shallow sea. The steep cliffs along the southern edge of the depression continue moving southward as they’re eroded by wind and run-off. When infrequent but intense rains pour down the channels of the southern cliffs, it carves away sediment which the water carries onward. In the flatter basin, these sometimes-rivers slow and spread out, eventually dropping the sediment they carry into sandbars. The build-up of sandbars causes the slower-moving water to shift its course back-and-forth over time, creating the alluvial fans seen along the southern and western borders. (Image credit: J. Stevens, via NASA Earth Observatory)

  • Martian Mantle Convection

    Martian Mantle Convection

    Over geological timescales – on the order of millions of years – even hard substances like rock can flow like a fluid. Heat from the Earth’s core drives convection inside our mantle, and that fluid motion ultimately drives the plate tectonics we experience here at the surface. But most other planetary bodies, including those with mantle convection similar to ours, don’t have a surface that shifts like our tectonic plates. Mars and Venus, for example, have solid, unmoving surfaces. The images above provide a peek at what goes on beneath. The upper image shows a simulation of mantle convection inside Mars over millions of years. The lower image is a timelapse of dye convecting through a layer of glucose syrup being heated from below. Notice how both examples show evidence of convective cells and plumes that help circulate warm fluid up and colder fluid downward. (Image credit: Mars simulation – C. Hüttig et al, source; N. Tosi et al., source; submitted by Nicola T.)

  • Jupiter’s Belts and Zones

    Jupiter’s Belts and Zones

    Jupiter’s distinctive bands of colored clouds, known as belts and zones, have been an iconic part of the planet since they were first observed by Galileo. (The scientist, not the space mission!) They are considered part of Jupiter’s weather layer, the region of its atmosphere where storms reign. Thanks to gravitational measurements by the Juno spacecraft, we now know how deep these bands persist; they stretch about 3,000 kilometers into Jupiter! That means that Jupiter’s weather layer accounts for about one percent of the planet’s total mass. By comparison, Earth’s entire atmosphere makes up less than one millionth of its mass. What lies beneath Jupiter’s colorful clouds is also intriguing. The same gravitational measurements that indicate the weather layer’s depth also suggest that, beneath these storms, the rest of Jupiter rotates like a solid body. (Image credit: NASA, source; research credit: Y. Kaspi et al., submitted by Kam-Yung Soh)

  • Fissures in Africa

    Fissures in Africa

    Pictures of an enormous fissure in Kenya’s East African Rift Valley have gone viral in recent weeks along with breathless reports about how part of the African continent is splitting away. And while Africa is splitting – very, very slowly – this crack, impressive as it is, may not have anything to do with it. Geologists familiar with the area are confident that the fissure is the result of recent torrential rains and flooding – not fresh seismic activity. For one, there have been no earthquakes in this area stretching back for several years. One theory is that the crack had actually been present for quite some time but was filled with softer volcanic ash that’s been swept away by the rains. Geologists will need to study it more closely to be certain.

    One thing geologists agree on, though, is that the tectonic plates that make up Africa are slowly pulling apart, or rifting. (That’s why the area is known as a rift valley in the first place.) This happens as mantle convection causes two land masses to move away from one another. That’s happening right now along a fault running through Ethiopia, Kenya, and Tanzania, and it’s happened before. A similar rift caused the South American and African continents to separate. This doesn’t mean that the countries in East Africa are in danger of being parted by ocean any time soon, though. Geologists predict it will take on the order of 50 million years for the break to happen. (Image credit: Getty Images; Reuters/T. Mukoya; DailyNation)

  • Dune Networks

    Dune Networks

    In sandy deserts, winds can build a vast network of dunes whose shapes depend on the winds that built them. This photograph, taken by an astronaut aboard the International Space Station, shows part of a Saharan dune field known as the Grand Erg Oriental. Of the five basic types of sand dunes, this field features all but one. The predominant winds of the region build most of the dunes into long, straight chains separated by interdune flats some 150 meters lower in elevation. Within the chains, there are linear dunes, created by winds blowing nearly parallel to the dune’s long axis. In places where winds tend to change directions, several linear dunes may merge to form star dunes, like the one just below and right of center in the image. Transverse dunes form perpendicular to the predominant wind direction. The one shown in the upper left of this image may have formed when multiple crescant-shaped barchan dunes merged. (Image credit: NASA, via NASA Earth Observatory)

  • Water on Mars

    Water on Mars

    Recurring slope lineae (RSL) are seasonal features on Mars that leave behind gullies similar to those left by running water on Earth. Their discovery a few years ago has prompted many experiments at Martian conditions to determine how these features form. At Martian surface pressures and temperatures, it’s not unusual for water to boil. And that boiling, as some experiments have shown, introduces opportunities for new transport mechanisms.

    Researchers found that water in “warm” (T = 288 K) sand boils vigorously, ejecting sand particles and creating larger pellets of saturated sand. Water continues boiling out of the pellets once they form, creating a layer of vapor that helps levitate them as they flow downslope. The effect is similar to the Leidenfrost effect with drops of water sliding on a hot skillet; there’s little friction between the pellet and the surface, allowing it to travel farther.

    The mechanism is quite efficient in experiments under Earth gravity and would be even more so under Mars’ lower gravity. It also requires less water than alternative explanations. The pellets that form are too small to be seen by the satellites we have imaging Mars, but the tracks they leave behind are similar to the RSL seen above. (Image credit: NASA; research credit: J. Raack et al., 1, 2; via R. Anderson; submitted by jpshoer)

  • Jovian Polar Vortices

    Jovian Polar Vortices

    Jupiter’s atmosphere is full of enduring mysteries, and its poles are no exception. Instruments aboard the Juno spacecraft have gotten a better look at Jupiter’s North and South poles than any previous mission, and what they’ve found raises even more questions. Both of Jupiter’s poles feature a central cyclone ringed by other, similarly-sized cyclones. The North pole has eight outer cyclones (top image), while the South pole has five (bottom image), shown above in infrared. Despite being close enough that their spiral arms intersect, the cyclones don’t seem to be merging into something like Saturn’s polar hexagon. For now, scientists don’t know how this arrangement formed or why it persists, but the longer Juno can study the vortices up close, the more we’ll learn. (Image credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM; research credit: A. Adriani et al.; submitted by Kam-Yung Soh)