Mass tree die-offs are sparking worries of fire in California’s Sierra Nevada range. An outbreak of bark beetles, along with persistent drought in the state, have caused many evergreen trees to wither and die.The damage spread rapidly through the mountains in the fall of 2015 after favorable spring conditions (warm and dry) led to a surge in beetle populations, according to Zach Tane, a remote sensing analyst with the U.S. Forest Service (USFS). The beetles burrow under a tree’s bark and lay their eggs. Once they penetrate the tree’s armor (the bark), they begin to gnaw into its living tissue, the phloem.“Needles don’t turn red the next day. It’s a slow process of the tree dying, and it has to do with life cycle of bark beetle and how long needles can persist in a green state,” said Tane. “As the population of beetles grows, they can overwhelm the natural defenses of a tree. There’s a tipping point—that’s what happened in Colorado and probably what’s happening here.”

This image from NASA's Dawn spacecraft shows Kupalo Crater, one of the youngest craters on Ceres. Image Credit: NASA/JPL Caltech/UCLA/MPS/DLR/IDAFeatures on dwarf planet Ceres that piqued the interest of scientists throughout 2015 stand out in exquisite detail in the latest images from NASA's Dawn spacecraft, which recently reached its lowest-ever altitude at Ceres.Dawn took these images near its current altitude of 240 miles (385 kilometers) from Ceres, between Dec. 19 and 23, 2015.Kupalo Crater, one of the youngest craters on Ceres, shows off many fascinating attributes at the high image resolution of 120 feet (35 meters) per pixel. The crater has bright material exposed on its rim, which could be salts, and its flat floor likely formed from impact melt and debris. Researchers will be looking closely at whether this material is related to the "bright spots" of Occator Crater. Kupalo, which measures 16 miles (26 kilometers) across and is located at southern mid-latitudes, is named for the Slavic god of vegetation and harvest.

Winter storms can blanket Iceland almost entirely with snow. The relative warmth of summer and fall, however, exposes a spectacular, varied landscape. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this natural-color view of the Nordic island nation on November 9, 2015.“The visible snow cover is typical for this time of the year, compared to conditions during the past 15-20 years,” said Thorsteinn Thorsteinsson, a glaciologist at the Icelandic Meteorologial Office. He noted, however, that compared to the reference period of 1961-1990, snow cover is “almost certainly” less than average in the highland and mountain regions above 400 meters in elevation.The melting of seasonal snow cover accentuates the boundaries of Iceland’s permanent ice caps. The ice caps appear smooth and rounded in contrast with the snow-covered interior plateau or the snow-capped ridges along the glacier-carved coastline.