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What Makes a Dune?

Wind and water can form sandy ripples in a matter of minutes. Most will be erased, but some can grow to meter-scale and beyond. What distinguishes these two fates? Researchers used a laser scanner to measure early dune growth in the Namib Desert to see. They found that the underlying surface played a big role in whether sand gathered or disappeared from a given spot. Surfaces like gravel, rock, or moistened sand were better for starting a dune than loose sand was. Each of these surface types affected how much sand the wind could carry off, as well as whether grains bounced or stuck where they landed. Every trapped sand grain made the surface a little rougher, increasing the chances of trapping the next sand grain. Over time, the gathering sand forms a bump that affects the wind flow nearby, further shaping the proto-dune. As long as the wind isn’t strong enough to scour the surface clean, it will keep gathering sand as the process continues. (Image credit: M. Gheidarlou; research credit: C. Rambert et al.; via Eos)

ufofeed.com/142205/do-you-thin Do you think sending probes directly to the sites where water and other liquids are being ejected is a better idea for accessing the subsurface oceans of Enceladus and Europa, rather than drilling multiple kilometers through the solid icy surface from scratch? #Astrobiology #Astrophysics #Cosmology #PlanetaryScience #Space #SpaceExploration

ufofeed.com/139944/in-a-very-u In a very unique setting over Earth’s colorful horizon, the silhouette of the space shuttle Endeavour is featured in this photo by an Expedition 22 crew member on board the International Space Station, as the shuttle approached for its docking on Feb. 9 during the STS-130 mission.Image Credit: NASA #Astrobiology #Astrophysics #Cosmology #PlanetaryScience #Space #SpaceExploration