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NASA Astronomy Picture of the Day:

What's happened in Hebes Chasma on Mars? Hebes Chasma is a depression just north of the enormous Valles Marineris canyon. Since the depression is unconnected to other surface features, it is unclear where the internal material went. Inside Hebes Chasma is Hebes Mensa, a 5 kilometer high mesa that appears to have undergone an unusual partial collapse -- a collapse that might be providing clues. The featured image, taken by ESA's robotic Mars Express spacecraft currently orbiting Mars, shows great details of the chasm and the unusual horseshoe shaped indentation in the central mesa. Material from the mesa appears to have flowed onto the floor of the chasm, while a possible dark layer appears to have pooled like ink on a downslope landing. One hypothesis holds that salty rock composes some lower layers in Hebes Chasma, with the salt dissolving in melted ice flows that drained through holes into an underground aquifer.

Pelagic stingray (Pteroplatytrygon violacea), Cape Palos, region of Murcia, Spain. This species of stingray has a worldwide distribution in waters warmer than 19 °C (66 °F), and migrates seasonally to spend the summer closer to the continental shelf and at higher latitudes. The only stingray that almost exclusively inhabits the open ocean, this species is typically found in surface waters down to a depth of 100 m (330 ft). The pelagic stingray typically grows to 1.3 m (4.3 ft) long and 59 cm (23 in) across. It's an active predator that captures prey by wrapping its pectoral fins around it, before manipulating it to the mouth. A wide variety of organisms are represented in its diet: crustaceans, molluscs, bony fishes, sea horses and filefish, comb jellies and medusae, and polychaete worms.

Diego Delso, CC BY-SA 4.0, via Wikimedia Commons. View source.

Island County, Washington

NASA Astronomy Picture of the Day:

What is going on with this galaxy? NGC 2685 is a confirmed polar ring galaxy - a rare type of galaxy with stars, gas and dust orbiting in rings perpendicular to the plane of a flat galactic disk. The bizarre configuration could be caused by the chance capture of material from another galaxy by a disk galaxy, with the captured debris strung out in a rotating ring. Still, observed properties of NGC 2685 suggest that the rotating helix structure is remarkably old and stable. In this sharp view of the peculiar system also known as Arp 336 or the Helix galaxy, the strange, perpendicular rings are easy to trace as they pass in front of the galactic disk, along with other disturbed outer structures. NGC 2685 is about 50,000 light-years across and 40 million light-years away in the constellation of the Great Bear (Ursa Major). Piece it All Together: Astronomy Puzzle of the Day

Photo by Stefan Thrun

A cavalryman of the French Republican Guard during the Bastille Day military parade. This regiment is responsible for special security duties in Paris (including guarding important public buildings) and for providing guards of honour at official ceremonies.

Jebulon, CC0, via Wikimedia Commons. View source.

NASA Astronomy Picture of the Day:

Why isn't this ant a big sphere? Planetary nebula Mz3 is being cast off by a star similar to our Sun that is, surely, round. Why then would the gas that is streaming away create an ant-shaped nebula that is distinctly not round? Clues might include the high 1000-kilometer per second speed of the expelled gas, the light-year long length of the structure, and the magnetism of the star featured here at the nebula's center. One possible answer is that Mz3 is hiding a second, dimmer star that orbits close in to the bright star. A competing hypothesis holds that the central star's own spin and magnetic field are channeling the gas. Since the central star appears to be so similar to our own Sun, astronomers hope that increased understanding of the history of this giant space ant can provide useful insight into the likely future of our own Sun and Earth. Explore Your Universe: Random APOD Generator

Seed pods of Heracleum sphondylium. Focus stack of 89 photos.

Agnes Monkelbaan, CC BY-SA 4.0, via Wikimedia Commons. View source.