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Hubble Chases a Small Stellar Galaxy in the Hunting Dog

by NASA’s Marshall Space Flight Center
 
On a clear evening in April of 1789, the renowned astronomer William Herschel continued his unrelenting survey of the night sky, hunting for new cosmic objects — and found cause to celebrate! He spotted this bright spiral galaxy, named NGC 4707, lurking in the constellation of Canes Venatici or The Hunting Dog. NGC 4707 lies roughly 22 million light-years from Earth. NGC stands for “New General Catalogue of Nebulae and Clusters of Stars.” Over two centuries later, the NASA/ESA Hubble Space Telescope is able to “chase down” and view the same galaxy in far greater detail than Herschel could, allowing us to appreciate the intricacies and characteristics of NGC 4707 as never before. This striking image comprises observations from Hubble’s Advanced Camera for Surveys (ACS), one of a handful of high-resolution instruments currently aboard the space telescope. Herschel himself reportedly described NGC 4707 as a “small, stellar” galaxy; while it is classified as a spiral (type Sm), its overall shape, center, and spiral arms are very loose and undefined, and its central bulge is either very small or non-existent. It instead appears as a rough sprinkling of stars and bright flashes of blue on a dark canvas. The blue smudges seen across the frame highlight regions of recent or ongoing star formation, with newborn stars glowing in bright, intense shades of cyan and turquoise. 

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Scientists Offer Sharper Insight into Pluto’s Bladed Terrain

by NASA’s Marshall Space Flight Center
 
Using a model similar to what meteorologists use to forecast weather and a computer simulation of the physics of evaporating ices, scientists have found evidence of snow and ice features on Pluto that, until now, had only been seen on Earth. Formed by erosion, the features, known as “penitentes,” are bowl-shaped depressions with blade-like spires around the edge that rise several hundreds of feet. The research, led by John Moores of York University, Toronto, and done in collaboration with scientists at the Johns Hopkins University Applied Physics Laboratory and NASA Goddard Space Flight Center, indicates that these icy features may also exist on other planets where environmental conditions are similar. The identification of these ridges in Pluto’s informally named Tartarus Dorsa area suggests that the presence of an atmosphere is necessary for the formation of penitentes – which Moores says would explain why they have not previously been seen on other airless icy satellites or dwarf planets. “But exotic differences in the environment give rise to features with very different scales,” he adds. “This test of our terrestrial models for penitentes suggests that we may find these features elsewhere in the solar system, and in other solar systems, where the conditions are right.“ The research team, which also includes York’s Christina Smith, Anthony Toigo of APL and Scott Guzewich of Goddard Space Flight Center, compared its model to ridges on Pluto imaged by NASA’s New Horizons spacecraft in 2015. Pluto’s ridges are much larger – more than 1,600 feet (about 500 meters) tall and separated by two to three miles (about three to five kilometers) – than their Earthly counterparts. “This gargantuan size is predicted by the same theory that explains the formation of these features on Earth,” says Moores. “In fact, we were able to match the size and separation, the direction of the ridges, as well as their age: three pieces of evidence that support our identification of these ridges as penitentes.” Moores says though Pluto’s environment is very different from Earth’s – it is much colder, the air much thinner, the sun much dimmer and the snow and ice on the surface are made from methane and nitrogen instead of water – the same laws of nature apply. He adds that both NASA and APL were instrumental in the collaboration that led to this new finding; both provided background information on Pluto’s atmosphere using a model similar to what meteorologists use to forecast weather on Earth. This was one of the key ingredients in Moores’ own models of the penitentes, without which this discovery would not have been made.