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)
Category: Phenomena
Bringing Beavers Back
It’s easy sometimes to forget just how drastically humans alter landscapes. Before European fur trappers came to North America, its waterways were ruled by beavers, one of nature’s most impressive engineers. Now researchers, ranchers, and conservationists are installing beaver dam analogs (BDAs) in streams and creeks to help bring back the beavers and their benefits.
Initially, the BDA starts as several human-driven posts with willow bark woven between. These structures help slow the water, which refills floodplains, deposits sediment, and can help recharge the water table. Beavers augment the structures and build new ones, helping bring complexity and fertility back to devastated waterways.
The benefits have been multifold. In waterways re-engineered through BDAs, native trout species have flourished, sage grouse nesting is recovering, water tables have climbed by a meter (thereby reducing irrigation costs), and seasonal streams have had their flow extended. It sounds like an exciting story, both for conservation and agriculture. Check out the full story here. (Video credit: Science; see also their full article)
Leaping Mobulas
Mobula rays are second only to manta rays in size, and, unlike their larger cousins, relatively little is known about them. Like other rays, they propel themselves by flapping their large pectoral fins, and they generate thrust through hydrodynamic lift. They’re quite efficient swimmers, able to generate enough thrust to leap over 2 meters out of the water before flopping back into it. Why the mobula rays jump and why they seem to prefer belly-flopping is unclear. They may be using the slap and splash to communicate with one another. When aggregations of mobulas are observed from overhead, jumping seems to occur along the outside of the group. Maybe this is an effort to attract more mobulas to a group or a method of scaring prey into the midst of the hunting mobulas. In any case, it is spectacular to behold firsthand. (Image credit: BBC; source)
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)
Kilauea’s Rivers of Lava
Kilauea continues to erupt without signs of abating. Aerial video, like this footage from Mick Kalber, shows the scope of the flow. Lava spurts like a hellish fountain from various fissures, then forms a gravity current that slowly flows downhill toward the ocean. Some of the angles give you an excellent view of the texture atop the flowing lava; it looks relatively rope-like now before solidification, indicating pahoehoe flow. Whether the flow will transition to the rougher appearance of a’a lava remains to be seen; as the lava cools and crystallizes, it may develop a yield strength. That would make it similar to fluids like your toothpaste, which only flow once a critical force is applied. Stay safe, Hawaiians! (Image and video credit: M. Kalber; via Colossal)
The Many Shapes of Fish
After visiting an aquarium or snorkeling near a reef, you may have wondered why fish come in so many different shapes. Given that all fish species need to get around underwater, why are some fish, like tuna, incredibly streamlined while others, like the box fish, are so, well, boxy? There are several major groupings for fish based on their shape and how they propel themselves, whether it’s by undulating their body and tail or primarily by flapping their fins. Which grouping a fish tends toward depends largely on its environment and needs. Open-water swimmers tend to use their bodies and tails. Their bodies are better streamlined, too, allowing them to outrace even some ships! Fish that live in more complicated environments, like along the seafloor or in a reef, tend to favor maneuverability over speed. These fish – which include rays, pufferfish, and surgeonfish – use their fins for their main propulsion. Many of these species are still faster swimmers than you or I, but their slower speeds have reduced their need for hydrodynamic streamlining, allowing these fish to evolve a wide variety of odd body shapes. (Video credit: TED-Ed)
Waves Below the Surface
Even a seemingly calm ocean can have a lot going on beneath the surface. Many layers of water at different temperatures and salinities make up the ocean. Both of those variables affect density, and one stable orientation for the layers is with lighter layers sitting atop denser ones. Any motion underwater can disturb the interface between those two layers, creating internal waves like the ones in this demo. In the actual ocean, these internal waves can be enormous – 800 meters or more in height! In regions like the Strait of Gibraltar where flowing tides encounter underwater topography, large internal waves are a daily occurrence. Internal waves can also show up in the atmosphere and are sometimes visible as long striped clouds. (Video and image credit: Cal Poly)
Rainbow Paint on a Speaker
Every year brings faster high-speed cameras and better quality imaging, so the Slow Mo Guys like to occasionally revisit topics they’ve done before, like paint vibrated on a speaker. The physics involved here are fantastic, so I’ll revisit the topic, too! In this version, Gav and Dan are using a pretty beefy speaker at a relatively high volume, so the paint gets a strong acceleration. As they note, the paint colors mix to brown almost immediately. In the high-speed footage, we can see why.
Watch how the individual strands of paint behave. As they fly upward, they stretch out and get thinner. That stretching has a side effect: it makes the paint spin. This is angular momentum of the paint being conserved. Just like a spinning ice skater who pulls his arms in, the paint spins faster as it gets thinner. This provides a lot of the mixing. Just look at how the different colors twist together! (Image and video credit: The Slow Mo Guys)
Sandy Wrinkles
Water flowing back and forth over sand quickly forms a field of dune-like wrinkles. On the upstream side, the flow is a little faster, and it picks up grains of sand. When the flow slows on the downstream side of a bump, the sand gets deposited. In this way, small bumps in the sand continue growing larger. A similar process between wind and sand forms enormous dunes here on Earth and on Mars. These smaller water-driven wrinkles are very common in tidal areas and in sandy creeks. They can even build up and break down such that they create periodic waves that surge down the stream. (Image and video credit: amàco et al.)
Kilauea’s Lava Lake
Hawaii’s Kilauea Volcano continues to erupt, sending magma flowing through multiple fissures. The U.S. Geological Survey has sounded a warning, however, that the volcano could erupt more explosively. Hot spot volcanoes like Hawaii’s generally have more basaltic lava, which has a lower viscosity than more silica-rich magmas like those seen on continental plates. That makes Hawaii’s volcanoes less prone to explosive detonations like the 1980 Mt. St. Helens eruption. With less viscous lava, there’s less likelihood of plugging a magma chamber and causing a deadly buildup of pressure from toxic gases.
But that doesn’t mean that there’s no risk. In particular, officials are concerned by the rapid draining of a lava lake near Kilauea’s summit. As illustrated below, if the lava level drops below the water table, that increases the likelihood of steam forming in the underground chambers through which lava flows. The rapid drainage has destabilized the walls around the lava lake, causing frequent rockfalls into the chamber. If those were to plug part of the chamber and cause a steam buildup, then there could be an explosive eruption that releases the pressure. To be clear: even if this were to happen, it would be nothing like the explosiveness of Mt. St. Helens. But it would include violent expulsions of rock and widespread ash-fall. (Image credits: USGS, source; via Gizmodo)
