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Hellas Planitia is the largest visible impact basin in the Solar System and hosts the lowest elevations on Mars' surface. This image from NASA's Mars Reconnaisance Orbiter (MRO) covers a small central portion of the basin and shows a dune field with lots of dust devil trails. In the middle, we see what appears to be long and straight "scratch marks" running down the dune slopes. If we look closer, we can see these scratch marks actually squiggle back and forth on their way down the dune. These scratch marks are linear gullies. Just like on Earth, high-latitude regions on Mars are covered with frost in the winter. However, the winter frost on Mars is made of carbon dioxide ice (dry ice) instead of water ice. We believe linear gullies are the result of this dry ice breaking apart into blocks, which then slide or roll down warmer sandy slopes, refining and carving as they go. The specific process that causes the formation and evolution of the squiggle pattern in linear gullies is a question scientists are still trying to answer.
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Astronomers took this image as they were observing an extraordinary exploding star – a supernova – near the galaxy’s central yellow core! The star rapidly evolved from a supernova containing very little hydrogen to one that is hydrogen-rich — in just one year. This rarely observed metamorphosis was luminous at high energies and provides unique insight into the poorly understood final phases of massive stars. By studying similar galaxies we hold a scientific mirror up to our own, allowing us to build a better understanding of our galactic environment, which we cannot always observe, and of galactic behavior and evolution as a whole. Credit: ESA/Hubble & NASA/D. Milisavljevic (Perdue University)