FYFD

Tag: planetary science

  • Titan’s Dust Storms

    Titan’s Dust Storms

    Earth and Mars are well-known for their dust storms, but a new source of extraterrestrial dust storms is joining them: Saturn’s moon Titan. Titan already shares unusual similarities to Earth: it is the only other place known to currently have stable liquid bodies at its surface. On Earth, water makes up our lakes and oceans; on Titan, it’s methane.

    The evidence that Titan may also have dust storms dates from several Cassini flybys in 2009 and 2010. Cassini observed short-lived infrared bright spots in a dune-covered equatorial region. After considering several other possible sources for these temporary bright spots, researchers concluded that the most likely explanation was dust clouds suspended by high winds. This suggests that the dune fields on Titan are still actively changing, just like those on Earth and Mars! (Image credit: artist’s concept for Titan dust storm – NASA/ESA/IPGP/Labex UnivEarthS/University Paris Diderot; research credit: S. Rodriguez et al.; submitted by jpshoer)

  • Zones and Stars

    Zones and Stars

    Large-scale rotating flows, like planetary atmospheres, tend to organize themselves into zones. Within a zone, flow remains essentially in an east-west direction and serves as a barrier that keeps heat or other elements from mixing from one zone to another. This is, for example, how the tropical trade winds work here on Earth.

    Stars, on the other hand, don’t show this kind of zonal behavior. The reason, it turns out, is their magnetic fields. When there’s no magnetic influence, even weak shear in a rotating flow is enough to start organizing turbulent fluctuations and grow a zonal flow. This tendency toward growth is known as the zonostrophic instability. But when you add a magnetic field, instead of organizing the hydrodynamic disturbances, that weak shear strengthens the magnetic ones, which in turn suppress the flow fluctuations. As a result, the hydrodynamic disturbances cannot grow and no zonal flow forms.

    Researchers think this mechanism can explain both why stars have no zonal flows and just how deep zones can penetrate inside the atmospheres of gas giants like Jupiter and Saturn before their planet’s magnetic field suppresses them. (Image credit: NASA; research credit: N. Constantinou and J. Parker, arXiv; via LLNL News; submitted by Stephanie N.)

  • Forming Europa’s Bands

    Forming Europa’s Bands

    Jupiter’s icy moons, Europa and Ganymede, are home to subsurface oceans. These moons also experience strong tidal forces from their parent planet and sibling moons that squeeze and deform them over time. A new study focuses on the bands, seen in red in the top image of Europa, that form as a result of these deformations. By simulating (bottom image) both the convective currents within the Europan ocean and the deformation of the ice over time, scientists are able to study how these geological surface features may have formed. Over the course of about a million years, material from the interior ocean works its way up into the center of a band. Because this process takes so long, the researchers point out that any attempt to collect material from the bands will yield “fossil” ocean material – essentially a glimpse of Europa’s ocean as it existed a million years ago rather than how it exists today! (Image credit: NASA; image and research credit: S. Howell and R. Pappalardo, source; submitted by Kam-Yung Soh)

  • 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)