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<!--StartFragment--><p class="MsoNormal"><b style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif;" class=""><font size="5" class="">NASA’s Cassini Mission Prepares for 'Grand Finale' at Saturn</font></b><br style="font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class=""></p><table align="center" width="687" cellpadding="1" style="margin: 0px 0px 10px; padding: 0px; border: 1px solid rgb(190, 191, 185); vertical-align: baseline; border-collapse: collapse; border-spacing: 0px; width: 708px; font-size: 0.923em; font-family: Arial, Helvetica, sans-serif;" class=""><tbody style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><td style="margin: 0px; padding: 10px; border: 1px solid rgb(230, 230, 230); vertical-align: middle;" class=""><div class="dnd-drop-wrapper" style="font-size: 14px; margin: 0px 0px 9px; padding: 0px; border: 0px; vertical-align: baseline;"><a href="https://www.nasa.gov/sites/default/files/thumbnails/image/cassinifinale.jpg" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189);" class=""><img typeof="foaf:Image" src="https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/cassinifinale.jpg" width="687px" height="auto" alt="This illustration shows NASA’s Cassini spacecraft above Saturn's northern hemisphere prior to one of its 22 grand finale dives. " title="" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""></a></div><div class="dnd-legend-wrapper" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><div class="caption" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><span style="font-size: 14px;" class="">This illustration shows NASA’s <span class="scayt-misspell-word" data-scayt-lang="en_US" data-scayt-word="Cassini" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Cassini</span> spacecraft above Saturn's northern hemisphere prior to one of its 22 grand finale dives.</span></div><b style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><i style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><div class="credits" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 14px;">Credits: NASA/<span class="scayt-misspell-word" data-scayt-lang="en_US" data-scayt-word="JPL-Caltech" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">JPL-Caltech</span></div></i></b><div class="link" style="font-size: 14px; margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><a href="#" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); font-size: 10px;" class=""></a></div></div></td></tr></tbody></table><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class="">NASA's Cassini spacecraft, in orbit around Saturn since 2004, is about to begin the final chapter of its remarkable story. On Wednesday, April 26, the spacecraft will make the first in a series of dives through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its rings as part of the mission’s grand finale. "No spacecraft has ever gone through the unique region that we'll attempt to boldly cross 22 times," said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "What we learn from Cassini’s daring final orbits will further our understanding of how giant planets, and planetary systems everywhere, form and evolve. This is truly discovery in action to the very end.” During its time at Saturn, Cassini has made numerous dramatic discoveries, including a <a href="https://www.nasa.gov/press-release/cassini-finds-global-ocean-in-saturns-moon-enceladus" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">global ocean</a> that showed indications of hydrothermal activity within the icy moon Enceladus, and <a href="https://www.nasa.gov/feature/jpl/cassini-explores-a-methane-sea-on-titan" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">liquid methane seas</a> on its moon Titan. Now 20 years since launching from Earth, and after 13 years orbiting the ringed planet, Cassini is running low on fuel. In 2010, NASA decided to end the mission with a purposeful plunge into Saturn this year in order to protect and preserve the planet's moons for future exploration – especially the potentially habitable Enceladus. But the beginning of the end for Cassini is, in many ways, like a whole new mission. Using expertise gained over the mission's many years, Cassini engineers designed a flight plan that will maximize the scientific value of sending the spacecraft toward its fateful plunge into the planet on Sept. 15. As it ticks off its terminal orbits during the next five months, the mission will rack up an impressive list of scientific achievements. "This planned conclusion for Cassini's journey was far and away the preferred choice for the mission's scientists," said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. "Cassini will make some of its most extraordinary observations at the end of its long life.” The mission team hopes to gain powerful insights into the planet's internal structure and the origins of the rings, obtain the first-ever sampling of Saturn's atmosphere and particles coming from the main rings, and capture the closest-ever views of Saturn's clouds and inner rings. The team currently is making final checks on the list of commands the robotic probe will follow to carry out its science observations, called a sequence, as it begins the finale. That sequence is scheduled to be uploaded to the spacecraft on Tuesday, April 11. Cassini will transition to its grand finale orbits, with a last close flyby of Saturn's giant moon Titan, on Saturday, April 22. As it has many times over the course of the mission, Titan's gravity will bend Cassini's flight path. Cassini's orbit then will shrink so that instead of making its closest approach to Saturn just outside the rings, it will begin passing between the planet and the inner edge of its rings. "Based on our best models, we expect the gap to be clear of particles large enough to damage the spacecraft. But we're also being cautious by using our large antenna as a shield on the first pass, as we determine whether it's safe to expose the science instruments to that environment on future passes," said Earl Maize, Cassini project manager at JPL. "Certainly there are some unknowns, but that's one of the reasons we're doing this kind of daring exploration at the end of the mission.” In mid-September, following a distant encounter with Titan, the spacecraft's path will be bent so that it dives into the planet. When Cassini makes its final plunge into Saturn's atmosphere on Sept. 15, it will send data from several instruments – most notably, data on the atmosphere's composition – until its signal is lost. "Cassini's grand finale is so much more than a final plunge," said Spilker. "It's a thrilling final chapter for our intrepid spacecraft, and so scientifically rich that it was the clear and obvious choice for how to end the mission.” Resources on Cassini's grand finale, including images and video, are available at: <strong style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class=""><a href="https://saturn.jpl.nasa.gov/mission/grand-finale/grand-finale-resources" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">https://saturn.jpl.nasa.gov/mission/grand-finale/grand-finale-resources</a> </strong>An animated video about Cassini's Grand Finale is available at: <strong style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><a href="https://youtu.be/xrGAQCq9BMU" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">https://youtu.be/xrGAQCq9BMU</a> </strong>The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate. JPL designed, developed and assembled the Cassini orbiter. More information about Cassini is at: <strong style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><a href="http://www.nasa.gov/cassini" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">http://www.nasa.gov/cassini</a> </strong><strong style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><a href="http://saturn.jpl.nasa.gov" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">http://saturn.jpl.nasa.gov</a></strong></p><div class=""><br class=""></div><div class=""><b style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class="">NASA's MAVEN Reveals Most of Mars' Atmosphere Was Lost to Space</b><br style="font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class=""><table align="center" width="687" cellpadding="1" style="margin: 0px 0px 10px; padding: 0px; border: 1px solid rgb(190, 191, 185); vertical-align: baseline; border-collapse: collapse; border-spacing: 0px; width: 708px; font-size: 0.923em; font-family: Arial, Helvetica, sans-serif;" class=""><tbody style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><td style="margin: 0px; padding: 10px; border: 1px solid rgb(230, 230, 230); vertical-align: middle;" class=""><div class="dnd-drop-wrapper" style="font-size: 14px; margin: 0px 0px 9px; padding: 0px; border: 0px; vertical-align: baseline;"><a href="https://www.nasa.gov/sites/default/files/thumbnails/image/mars_landscape_dry_wet.png" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class=""><img typeof="foaf:Image" src="https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/mars_landscape_dry_wet.png" width="687px" height="auto" alt="This artist’s concept depicts the early Martian environment and Mars as seen today." title="" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""></a></div><div class="dnd-legend-wrapper" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><div class="caption" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><span style="font-size: 14px;" class="">This artist’s concept depicts the early Martian environment (right) – believed to contain liquid water and a thicker atmosphere – versus the cold, dry environment seen at Mars today (left). NASA's Mars Atmosphere and Volatile Evolution is in orbit of the Red Planet to study its upper atmosphere, ionosphere and interactions with the sun and solar wind. </span></div><b style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><i style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><div class="credits" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 14px;">Credits: NASA’s Goddard Space Flight Center</div></i></b><div class="link" style="font-size: 14px; margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;"><a href="#" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); font-size: 10px;" class=""></a></div></div></td></tr></tbody></table><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class="">Solar wind and radiation are responsible for stripping the Martian atmosphere, transforming Mars from a planet that could have supported life billions of years ago into a frigid desert world, according to new results from NASA's MAVEN spacecraft. "We've determined that most of the gas ever present in the Mars atmosphere has been lost to space," said Bruce Jakosky, principal investigator for the Mars Atmosphere and Volatile Evolution Mission (MAVEN), University of Colorado in Boulder. The team made this determination from the latest results, which reveal that about 65 percent of the argon that was ever in the atmosphere has been lost to space. Jakosky is lead author of a paper on this research to be published in Science on Friday, March 31. In 2015, MAVEN team members <a href="https://www.nasa.gov/press-release/nasa-mission-reveals-speed-of-solar-wind-stripping-martian-atmosphere" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">previously announced results</a> that showed atmospheric gas is being lost to space today and described how atmosphere is stripped away. The present analysis uses measurements of today’s atmosphere for the first estimate of how much gas was lost through time. Liquid water, essential for life, is not stable on Mars' surface today because the atmosphere is too cold and thin to support it. However, evidence such as features resembling dry riverbeds and minerals that only form in the presence of liquid water indicates the ancient Martian climate was much different – warm enough for water to flow on the surface for extended periods.</p><div style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif; font-size: 18px;" class=""><br class="webkit-block-placeholder"></div><table align="right" width="33%" cellpadding="1" style="margin: 0px 0px 10px; padding: 0px; border: 1px solid rgb(190, 191, 185); vertical-align: baseline; border-collapse: collapse; border-spacing: 0px; width: 232px; font-size: 0.923em; font-family: Arial, Helvetica, sans-serif; float: right; clear: right;" class=""><tbody style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><td style="margin: 0px; padding: 10px; border: 1px solid rgb(230, 230, 230); vertical-align: middle;" class=""><span style="font-size: 14px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><img src="https://www.nasa.gov/sites/default/files/styles/side_image/public/thumbnails/image/mavenargoninfographic2.jpg" title="" width="200px" height="auto" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""></span><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><span style="font-size: 14px;" class="">This infographic shows how Mars lost argon and other gasses over time due to ‘sputtering.’ Click to enlarge.</span></p><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><b style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><i style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; font-size: 14px;" class="">Credits: NASA’s Goddard Space Flight Center</i></b></p><a href="http://svs.gsfc.nasa.gov/1255" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none; font-size: 14px;" class="">http://svs.gsfc.nasa.gov/12557</a></td></tr></tbody></table><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif;" class=""><font size="4" class="">“This discovery is a significant step toward unraveling the mystery of Mars' past environments,“ said Elsayed Talaat, MAVEN Program Scientist, at NASA Headquarters in Washington. “In a broader</font></p><p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: Arial, Helvetica, sans-serif;" class=""><font size="4" class="">context, this information teaches us about the processes that can change a planet’s habitability over time.” There are many ways a planet can lose some of its atmosphere. For example, chemical reactions can lock gas away in surface rocks, or an atmosphere can be eroded by radiation and a stellar wind from a planet's parent star. The new result reveals that solar wind and radiation were responsible for most of the atmospheric loss on Mars, and the depletion was enough to transform the Martian climate. The solar wind is a thin stream of electrically conducting gas constantly blowing out from the surface of the sun. The early Sun had far more intense ultraviolet radiation and solar wind, so atmospheric loss by these processes was likely much greater in Mars' history. According to the team, these processes may have been the dominant ones controlling the planet's climate and habitability. It's possible microbial life could have existed at the surface early in Mars’ history. As the planet cooled off and dried up, any life could have been driven underground or forced into rare surface oases. Jakosky and his team got the new result by measuring the atmospheric abundance of two different isotopes of argon gas. Isotopes are atoms of the same element with different masses. Since the lighter of the two isotopes escapes to space more readily, it will leave the gas remaining behind enriched in the heavier isotope. The team used the relative abundance of the two isotopes measured in the upper atmosphere and at the surface to estimate the fraction of the atmospheric gas that has been lost to space. As a "noble gas" argon cannot react chemically, so it cannot be sequestered in rocks; the only process that can remove noble gases into space is a physical process called "sputtering" by the solar wind. In sputtering, ions picked up by the solar wind can impact Mars at high speeds and physically knock atmospheric gas into space. The team tracked argon because it can be removed only by sputtering. Once they determined the amount of argon lost by sputtering, they could use this information to determine the sputtering loss of other atoms and molecules, including carbon dioxide (CO<sub style="margin: 0px; padding: 0px; border: 0px; line-height: normal;" class="">2</sub>). CO<sub style="margin: 0px; padding: 0px; border: 0px; line-height: normal;" class="">2</sub> is of interest because it is the major constituent of Mars' atmosphere and because it's an efficient greenhouse gas that can retain heat and warm the planet. "We determined that the majority of the planet's CO<sub style="margin: 0px; padding: 0px; border: 0px; line-height: normal;" class="">2</sub> was also lost to space by sputtering," said Jakosky. "There are other processes that can remove CO<sub style="margin: 0px; padding: 0px; border: 0px; line-height: normal;" class="">2</sub>, so this gives the minimum amount of CO<sub style="margin: 0px; padding: 0px; border: 0px; line-height: normal;" class="">2</sub> that's been lost to space.” The team made its estimate using data from the Martian upper atmosphere, which was collected by MAVEN's Neutral Gas and Ion Mass Spectrometer (NGIMS). This analysis included measurements from the Martian surface made by NASA's Sample Analysis at Mars (SAM) instrument on board the Curiosity rover. "The combined measurements enable a better determination of how much Martian argon has been lost to space over billions of years," said Paul Mahaffy of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Using measurements from both platforms points to the value of having multiple missions that make complementary measurements." Mahaffy, a co-author of the paper, is principal investigator on the SAM instrument and lead on the NGIMS instrument, both of which were developed at NASA Goddard. The research was funded by the MAVEN mission. MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder, and NASA Goddard manages the MAVEN project. MSL/Curiosity is managed by NASA's Jet Propulsion Laboratory, Pasadena, California. For more information on MAVEN, visit: <strong style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;" class=""><a href="http://www.nasa.gov/maven" style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: rgb(0, 116, 189); text-decoration: none;" class="">http://www.nasa.gov/maven</a></strong></font></p><div class=""><br class=""></div><div class=""><div class="title-bar" style="box-sizing: border-box; margin: 2em 0px;"><div class="title-wrap" style="box-sizing: border-box; width: 738.75px; padding: 0px;"><h1 class="title" style="box-sizing: border-box; margin: 0px; font-family: inherit; line-height: 1.1; color: inherit; font-size: 2.2em;">Space Station View of Auroras</h1></div></div><div class="feature-image-container" style="box-sizing: border-box; margin: 0px -2em 2em;"><a href="https://www.nasa.gov/sites/default/files/thumbnails/image/33584905191_5f0a2300b5_oa.jpg" data-bindattr-959="959" style="box-sizing: border-box; color: rgb(42, 100, 150); outline: 0px; background-position: 0px 0px;" class=""></a></div></div></div></div></body></html>