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Luhmann J.G.,University of California at Berkeley | Ma Y.J.,University of California at Los Angeles | Villarreal M.N.,University of California at Los Angeles | Wei H.Y.,University of California at Los Angeles | Zhang T.L.,Institute for Space Research
Planetary and Space Science | Year: 2015

The Venus solar wind interaction is often regarded as the prototypical example of an induced magnetosphere. Pioneer Venus Orbiter (PVO) observations during a period of moderate to strong solar EUV fluxes led to a fairly detailed picture in which the currents in the conducting ionosphere produce a nearly impenetrable obstacle to the incident magnetized plasma flow, resulting in a classical draped field magnetosheath region and a comet-like magnetotail. Inspired by the availability of Venus Express (VEX) observations from the north polar region, and their sometimes unexpected behavior, we reanalyzed the observed Venus wake magnetic fields in the altitude range ~150 to ~450 km to determine whether some signature of a weak planetary field could have been missed. Our results suggest the presence of a small (few nT) but persistent radial field direction bias in the deep nightside, low to mid-latitude range sampled on PVO. The bias has a hemispheric dependence, with the more positive (outward) fields in the south and the more negative (inward) fields in the north. However the VEX counterpart of these data, obtained just nightward of the north polar terminator, shows no significant bias. This observation raises several questions about our understanding of the fields at the surface of Venus. We investigate whether the PVO radial field bias could be the subtle signature of a weak global dipole with, higher by ~10× than the previously established upper limits. A weak dipole solar wind interaction model produces results in the center of the low altitude wake that compare favorably with the observed field bias seen by PVO; however, the lack of agreement with the higher latitude and VEX observations suggests other explanations need to be considered. For example, effects related to previously observed convection electric field-controlled hemispheric asymmetries provide a possible alternative, as are external fields that diffuse into and through the interior. This work points out the need for better understanding the features introduced by species-dependent plasma processes, and the role of the planet itself, in deciphering weakly magnetized planet interactions. © 2015 Elsevier Ltd. Source

News Article | October 22, 2015
Site: http://www.techtimes.com/rss/sections/space.xml

Stars: Watch out. There's a black hole out there, waiting to eat you alive. You've heard of black holes. They are places in space where the gravity is so intense, nothing can get out, not even light. Hence, the term "black hole." We know they exist, but we can't actually see them, because they swallow all the light around them. So, the best way to spot them is to look for objects that are acting like they are near a black hole. Say, a star. When a star gets near a black hole, it's sucked in by what are called "tidal forces," which can rip that star into pieces. That process is called, appropriately, a "tidal disruption," which is kind of an understatement. Nothing is quite so disruptive as getting pulled apart. When the stars are clobbered in this way, it causes a solar flare that can last for years, giving astronomers evidence that the star was there. This week, a team of astronomers from the University of Maryland announced that members have observed a tidal disruption in a galaxy 290 million light years from Earth. It's the biggest tidal disruption they've seen in a decade. They gave it the foreboding name ASASSN-14li. The "assassin" was spotted because of its distinctive X-ray gases. The X-rays are created when pieces of the star are pulled into the black hole, heat up, and bubble out in X-ray gases. Once the scientists had identified the X-rays, they tapped colleagues at NASA and the European Space Agency to get a clearer picture of what was going on. "We have seen evidence for a handful of tidal disruptions over the years and have developed a lot of ideas of what goes on," said lead author Jon Miller, a professor of astronomy at the University of Michigan, in a press release. "This one is the best chance we have had so far to really understand what happens when a black hole shreds a star." Although we think of black holes as eating everything in sight, they actually do have a limit to what they can swallow, so they end up repelling some of the debris headed their way. This includes gases and winds that are prime for studying. "The black hole tears the star apart and starts swallowing material really quickly, but that's not the end of the story," said study coauthor Jelle Kaastra, an astronomer at the Institute for Space Research in the Netherlands. "The black hole can't keep up that pace so it expels some of the material outwards." By studying these black hole survivors, the scientists can get a better picture of what actually happens in the mysterious death traps. The surviving gases are, in a sense, ambassadors for the pieces of planetary debris that will never return. The research is described in a paper published in the Oct. 22 issue of the journal Nature.

Jain N.,University of Maryland University College | Sharma A.S.,University of Maryland University College | Zelenyi L.M.,Institute for Space Research | Malova H.V.,Institute for Space Research
Annales Geophysicae | Year: 2012

An electron-magnetohydrodynamic model is used to simulate the structure of an electron scale current sheet during early phase of collisionless magnetic reconnection. The current sheet develops structures, viz. bifurcated, filamented and triple-peak structures at different locations in the current sheet. The reversal of the net out-of-plane electric field seen by electrons bifurcates the current sheet in the outflow regions, the individual peaks having scale sizes of a few electron skin depths. Secondary instabilities of the bifurcated CS lead to its filamentation in the outflow and separatrix regions while triple-peak structures form at reconnection sites. These structures have implications for the forthcoming NASA/MMS mission designed to resolve electron space and time scales in the magnetosphere. © 2012 Author(s). Source

Fedorenko A.K.,Institute for Space Research | Kryuchkov E.I.,Institute for Space Research
Geomagnetism and Aeronomy | Year: 2011

The peculiarities of the distribution of medium-scale acoustic gravity waves (AGWs) in polar regions according to the data of measurements on board the Dynamics Explorer 2 satellite are studied. Over polar regions of both hemispheres at heights of 250-400 km, wave variations in neutral atmospheric parameters were systematically registered. These variations were identified as AGWs with horizontal wavelengths of 500-650 km. The relative amplitudes of polar AGWs in a neutral concentration reach 10%. Wave trains extend over the polar caps to thousands of kilometers and show a distinct spatial relationship with the auroral oval. A systematic direction is found in AGW propagation from the nighttime sector of the oval into the day-time sector, where wave activity is strictly limited. An assumption is formulated that this restriction is caused by dynamic interactions between AGWs and the zonal wind in the daytime sector of the auroral oval. © 2011 Pleiades Publishing, Ltd. Source

Belyayev S.M.,Institute for Space Research | Belyayev S.M.,KTH Royal Institute of Technology | Dudkin F.L.,Institute for Space Research
Review of Scientific Instruments | Year: 2016

Small weight and dimensions of the micro- A nd nanosatellites constrain researchers to place electromagnetic sensors on short booms or on the satellite body. Therefore the electromagnetic cleanliness of such satellites becomes a central question. This paper describes the theoretical base and practical techniques for determining the parameters of DC and very low frequency magnetic interference sources. One of such sources is satellite magnetization, the reduction of which improves the accuracy and stability of the attitude control system. We present design solutions for magnetically clean spacecraft, testing equipment, and technology for magnetic moment measurements, which are more convenient, efficient, and accurate than the conventional ones. © 2016 AIP Publishing LLC. Source

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