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NEWSCIENCENEWSCIENCENEWSCIENCE SCIENTISTS FIND SURPRISING Ribbon at Edge of Our Solar System: atoms, obtained last year by IBEX, CHANGES AT SOLAR BOUNDARY | Will the Sun Enter a Million-Degree showed a surprising arc-like feature hen NASA launched the} Cloud of Interstellar Gas? called the Ribbon. This astonishing \ \ } Interstellar Boundary Explorer cientists from the Space Research discovery was later announced by (IBEX) on 19 October 2008, space Centre of the Polish Academy of NASA as one of the most important physicists held their collective breath for} Sciences, Los Alamos National findings in space exploration made never-before-seen views of a collision zone | Laboratory, Southwest Research in 2009. Shortly after the discovery, far beyond the planets, roughly 10 billion | Institute and Boston University six hypotheses were proposed to miles away. That's where the solar wind, | suggest that the ribbon of enhanced explain the Ribbon, all of them an outward rush of charged particles and | emissions of energetic neutral atoms predicting its relationship to magnetic fields continuously spewed by | (ENAs), discovered last year by the processes going on within the the Sun, runs into the flow of particles and | NASA Small Explorer satellite IBEX, heliosphere or in its neighbourhood. fields that permeates interstellar space in | could be explained by a geometric In a paper published in Astrophysical our neighbourhood of the Milky Way | effect coming up because of the Journal Letters, a Polish-US team of galaxy. approach of the Sun to the boundary scientists, led by Professor Stan No spacecraft had ever imaged the | between the Local Cloud of Grzedzielski from the Space Research collision zone, which occurs in a | interstellar gas and another cloud of Centre in Warsaw, Poland, offers a region known as the heliosheath, | very hot gas called the Local Bubble. different explanation. "We observe because it emits no light. But the two | If this hypothesis is correct, IBEX is the Ribbon," says Prof. Grzedzielski, detectors on IBEX are designed to} catching matter from a hot "because the Sun is approaching a "see" what the human eye cannot. | neighbouring interstellar cloud, which boundary between our Local Cloud The interaction of the solar wind and | the Sun might enter in 100 years’ of interstellar gas and another cloud interstellar medium creates energetic | time. of a very hot and turbulent gas." neutral atoms (ENAs) of hydrogen The first full-sky maps of the (Source: ScienceDaily.com, 24 May 2010, which zip away from the heliosheath | emissions of energetic neutral http://tinyurl.com/23v8hIm) in all directions. Some of these atoms pass near Earth, where IBEX records their arrival direction and energy. As the spacecraft slowly spins, the detectors gradually build up pictures of the ENAs as they arrive from all over the sky. ‘ Mission scientists got their first Ribbon surprise six months after launch, once , ws oalitabiic the spacecraft had scanned enough overlapping strips of sky to create a complete 360° map. Instead of recording a_ relatively even distribution all the way around, as expected, IBEX found that the counts of ENAs—and thus the strength of the interaction in the heliosheath—varied dramatically from place to place. The detectors even discovered a long enhanced "ribbon", accentuated by an especially intense hotspot or "knot" arcing across the sky. Now scientists have finished assembling a second complete sweep around the sky, and IBEX has again delivered an unexpected result: the * Local Bubble The Sun, travelling through the Milky Way galaxy, happens to be crossing a blob of gas about 10 light-years across with a temperature of 6000-7000 degrees Kelvin. This so-called Local Interstellar Cloud is immersed in a much larger expanse of a million-degree hot gas, named the Local Bubble. The energetic neutral atoms (ENAs) are generated by charge exchange at the interface between the two gaseous media. ENAs can be observed, provided that the Sun is close enough to the interface. (Source: mickey | SRC/Tentaris, ACh/Maciej Frolow) NEXUS ¢ 51 DECEMBER 2010 - JANUARY 20II www.nexusmagazine.com