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TOPIC: IBEX Mission


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Title: Local Interstellar Hydrogen's Disappearance at 1 Au: Four Years of IBEX in the Rising Solar Cycle
Authors: Lukas Saul, Maciej Bzowski, Stephen Fuselier, Marzena Kubiak, Dave McComas, Eberhard Möbius, Justina Sokó, Diego Rodríguez, Juergen Scheer, Peter Wurz

NASA's Interstellar Boundary Explorer (IBEX) mission has recently opened a new window on the interstellar medium (ISM) by imaging neutral atoms. One "bright" feature in the sky is the interstellar wind flowing into the solar system. Composed of remnants of stellar explosions as well as primordial gas and plasma, the ISM is by no means uniform. The interaction of the local ISM with the solar wind shapes our heliospheric environment with hydrogen being the dominant component of the very local ISM. In this paper, we report on direct sampling of the neutral hydrogen of the local ISM over four years of IBEX observations. The hydrogen wind observed at 1 AU has decreased and nearly disappeared as the solar activity has increased over the last four years; the signal at 1 AU has dropped off in 2012 by a factor of ~8 to near background levels. The longitudinal offset has also increased with time presumably due to greater radiation pressure deflecting the interstellar wind. We present longitudinal and latitudinal arrival direction measurements of the bulk flow as measured over four years beginning at near solar minimum conditions. The H distribution we observe at 1 AU is expected to be different from that outside the heliopause due to ionisation, photon pressure, gravity, and filtration by interactions with heliospheric plasma populations. These observations provide an important benchmark for modelling of the global heliospheric interaction. Based on these observations we suggest a further course of scientific action to observe neutral hydrogen over a full solar cycle with IBEX.

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A Major Step Forward in Explaining the Ribbon in Space Discovered by NASAs IBEX Mission

724750main1_1_AP_IBEX_combined_1.74-670.jpg

The vast edges of our solar system - the boundary at the edge of our heliosphere where material streaming out from the sun interacts with the galactic material - is essentially invisible. It emits no light and no conventional telescope can see it. However, particles from inside the solar system bounce off this boundary and neutral atoms from that collision stream inward. Those particles can be observed by instruments on NASAs Interstellar Boundary Explorer (IBEX). Since those atoms act as fingerprints for the boundary from which they came, IBEX can map that boundary in a way never before done. In 2009, IBEX saw something in that map that no one could explain: a vast ribbon dancing across this boundary that produced many more energetic neutral atoms than the surrounding areas.
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 IBEX: Observing the Sun's Horizon

The Interstellar Boundary Explorer, or IBEX, is the first mission designed to map the entire region of the boundary of our Solar System. As charged particles from the Sun, called the "solar wind," flow outward well beyond the orbits of the planets, they collide with the material between the stars, called the "interstellar medium" (ISM). These interactions create energetic neutral atoms (ENAs), particles with no charge that move very quickly. This region emits no light that can be collected by conventional telescopes so, instead, IBEX, measures the particles that happen to be travelling inward from the boundary. IBEX contains two detectors designed to collect and measure ENAs, providing data about the mass, location, direction of origin, and energy of these particles. From these data, maps of the boundary are created. IBEX's sole, focused science objective is to discover the nature of the interactions between the solar wind and the interstellar medium at the edge of our Solar System.



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IBEX - New Observations of Interstellar Matter - Briefing Materials

NASA will host a Science Update to discuss new analysis from NASA's Interstellar Boundary Explorer (IBEX) spacecraft of material from outside our solar system and the interstellar boundary region that surrounds our home in space.
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Back in October 2009, we announced IBEXs first major science results, including the observation of what has become known as the "IBEX Ribbon." Since that time, IBEX has been detecting energetic neutral atoms coming from the boundary of our Solar System and from regions of our Earths magnetosphere, and we have periodically updated the IBEX website with information on these topics.
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A NASA spacecraft has uncovered the solar system's "nose," which points in the direction our sun is moving through the Milky Way galaxy, astronomers say.

In 2009 IBEX revealed a vast ribbon of atoms snaking its way along the solar system's edge. While intriguing, this ribbon was preventing astronomers from mapping the entire heliosphere.
Now Nathan Schwadron of the University of New Hampshire and his team have finally been able to digitally subtract the intense emissions given off by this mysterious ribbon, revealing the heliosphere's nose. This feature, like the bow of a ship, appears at the leading edge of the windsock-like heliosphere.

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IBEX Scientists Isolate Mysterious "Ribbon" of Energy and Particles that Wraps Around Solar System Boundary

In a paper to be published in the April 10, 2011, issue of The Astrophysical Journal, scientists on NASA's Interstellar Boundary Explorer (IBEX) mission, including lead author Nathan Schwadron and others from the University of New Hampshire, isolate and resolve the mysterious "ribbon" of energy and particles the spacecraft discovered in the heliosphere - the huge bubble that surrounds our solar system and protects us from galactic cosmic rays.
The finding, which overturns 40 years of theory, provides insight into the fundamental structure of the heliosphere, which in turn helps scientists understand similar structures or "astrospheres" that surround other star systems throughout the cosmos.

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The science just keeps coming from IBEX! We are heavily involved in analysing not only the particles coming from our heliosphere but also particles coming from regions that are much closer to home. In our August 2010 IBEX Update, we showed the first images of the dayside magnetosphere from IBEX. In our latest paper, presented today at the American Geophysical Union meeting in San Francisco, and awaiting publication in the Journal for Geophysical Research we show how IBEX can study the Earth's night side magnetosphere with unparalleled detail, including publication of the very first image of a region of our magnetosphere called the "plasma sheet." IBEX gives scientists yet another way to study this normally invisible part of our region of space. Read on for more information about this exciting news, including an unexpected observation.
The part of the magnetosphere that IBEX has imaged for the first time is the "plasma sheet". The plasma sheet is a component of the magnetotail made up of magnetic field lines that attach to the Earth at both ends, bottling up a denser region of positively charged atoms and negatively charged electrons. Missions like TWINS and IMAGE detected ENAs within about 30,000 miles of Earth and looking down the magnetotail. IBEX can observe them coming from much farther away from Earth in the plasma sheet.

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Solar System to Enter Million-Degree Cloud of Interstellar Gas?

Is the Sun going to enter a million-degree galactic cloud of interstellar gas soon?
Scientists from the Space Research Centre of the Polish Academy of Sciences, Los Alamos National Laboratory, Southwest Research Institute, and Boston University suggest that the ribbon of enhanced emissions of energetic neutral atoms, discovered last year by the NASA Small Explorer satellite IBEX, could be explained by a geometric effect coming up because of the approach of the Sun to the boundary between the Local Cloud of interstellar gas and another cloud of a very hot gas called the Local Bubble. If this hypothesis is correct, IBEX is catching matter from a hot neighbouring interstellar cloud, which the Sun might enter in a hundred years.

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Title: A possible generation mechanism for the IBEX ribbon from outside the heliosphere
Authors: S. Grzedzielski (1), M. Bzowski (1), A. Czechowski (1), H.O. Funsten (2), D.J. McComas (3), N.A. Schwadron (4) ((1) Space Research Centre PAS, Warsaw, Poland, (2) Los Alamos National Lab, Los Alamos NM, (3) Southwest Research Institute, San Antonio TX, (4) Boston University, Boston MA)

The brightest and most surprising feature in the first all-sky maps of Energetic Neutral Atoms (ENA) emissions (0.2-6 keV) produced by the Interstellar Boundary Explorer (IBEX) is an almost circular ribbon of a ~140{\deg} opening angle, centred at (l,b) = (33{\deg}, 55{\deg}), covering the part of the celestial sphere with the lowest column densities of the Local Interstellar Cloud (LIC). We propose a novel interpretation of the IBEX results based on the idea of ENA produced by charge-exchange between the neutral H atoms at the nearby edge of the LIC and the hot protons of the Local Bubble (LB). These ENAs can reach the Sun's vicinity because of very low column density of the intervening LIC material. We show that a plane-parallel or slightly curved interface layer of contact between the LIC H atoms (n_H = 0.2 cm^-3, T = 6000-7000 K) and the LB protons (n_p = 0.005 cm^-3, T ~ 10^6 K), together with indirect contribution coming from multiply-scattered ENAs from the LB, may be able to explain both the shape of the ribbon and the observed intensities provided that the edge is < (500-2000) AU away, the LIC proton density is (correspondingly) < (0.04-0.01) cm^-3, and the LB contains ~1% of non-thermal protons over the IBEX energy range. If this model is correct, then IBEX, for the first time, has imaged in ENAs a celestial object from beyond the confines of the heliosphere and can directly diagnose the plasma conditions in the LB.

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