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NASA's Cassini, Voyager Missions Suggest New Picture of Sun's Interaction with Galaxy

New data from NASA' Cassini mission, combined with measurements from the two Voyager spacecraft and NASA's Interstellar Boundary Explorer, or IBEX, suggests that our sun and planets are surrounded by a giant, rounded system of magnetic field from the sun - calling into question the alternate view of the solar magnetic fields trailing behind the sun in the shape of a long comet tail.
The sun releases a constant outflow of magnetic solar material - called the solar wind - that fills the inner solar system, reaching far past the orbit of Neptune. This solar wind creates a bubble, some 23 billion miles across, called the heliosphere. Our entire solar system, including the heliosphere, moves through interstellar space. The prevalent picture of the heliosphere was one of comet-shaped structure, with a rounded head and an extended tail. But new data covering an entire 11-year solar activity cycle show that may not be the case: the heliosphere may be rounded on both ends, making its shape almost spherical

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NASA-Funded Study Finds Two Solar Wind Jets in the Heliosphere

New NASA-funded research found that the giant bubble around our solar system, the heliosphere, is much shorter and smaller than previously thought, dominated by two jets shooting out the north and south poles of the sun.
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Title: Why are the magnetic field directions measured by Voyager 1 on both sides of the heliopause so similar?
Author: Jolanta Grygorczuk, Andrzej Czechowski, Stanislaw Grzedzielski

The solar wind carves in the interstellar plasma a cavity bounded by a surface, called the heliopause (HP), that separates the plasma and magnetic field of solar origin from the interstellar ones. It is now generally accepted that in August 2012 Voyager 1 (V1) crossed that boundary. Unexpectedly, the magnetic fields on both its sides, although theoretically independent of each other, were found to be similar in direction. This delayed the identification of the boundary as the heliopause and led to many alternative explanations. Here we show that the Voyager 1 observations can be readily explained and, after the Interstellar Boundary Explorer (IBEX) discovery of the ribbon, could even have been predicted. Our explanation relies on the fact that the Voyager 1 and the undisturbed interstellar field directions (which we assume to be given by the IBEX ribbon center (RC)) share the same heliolatitude (~34.5 degrees) and are not far separated in longitude (difference ~27 degrees). Our result confirms that Voyager 1 has indeed crossed the heliopause and offers the first independent confirmation that the IBEX ribbon center is in fact the direction of the undisturbed interstellar magnetic field. For Voyager 2 we predict that the difference between the inner and the outer magnetic field directions at the heliopause will be significantly larger than the one observed by Voyager 1 (~30 degrees, instead of ~20 degrees), and that the outer field direction will be close to the RC.

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Title: The Structure of The Heliopause
Authors: J. J. Quenby, W. R. Webber

Voyager 1 has explored the solar wind-interstellar medium interaction region between the Terminal Shock and the Heliopause, following the intensity distribution of the shock accelerated anomalous component of cosmic rays in the MeV energy range. The sudden disappearance of this component at 121.7 AU from the sun is discussed in terms of three models for the transition into the interstellar plasma flow. Particles trapped flowing parallel to the boundary may penetrate up to one Larmour radius beyond. If the boundary is stationary, Voyager 1 directly samples this distance. The boundary could flap, depending on Heliosheath pressure changes and Voyager 1 then samples the extent of this motion. Finally, a turbulent boundary layer is considered in which the MeV particle distribution falls off with distance, thus measuring diffusion within the layer.

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Title: Propagation into the heliosheath of a large-scale solar wind disturbance bounded by a pair of shocks
Authors: E. Provornikova, M. Opher, V. Izmodenov, G. Toth

After the termination shock (TS) crossing, the Voyager 2 spacecraft has been observing strong variations of the magnetic field and solar wind parameters in the heliosheath. Anomalous cosmic rays, electrons, and galactic cosmic rays present strong intensity fluctuations. Several works suggested that the fluctuations might be attributed to spatial variations within the heliosheath. Additionally, the variability of the solar wind in this region is caused by different temporal events that occur near the Sun and propagate to the outer heliosphere. To understand the spatial and temporal effects in the heliosheath, it is important to study these effects separately. In this work we explore the role of shocks as one type of temporal effects in the dynamics of the heliosheath. Although currently plasma in the heliosheath is dominated by solar minima conditions, with increasing solar cycle shocks associated with transients will play an important role. We used a 3D MHD multi-fluid model of the interaction between the solar wind and the local interstellar medium to study the propagation of a pair of forward-reverse shocks in the supersonic solar wind, interaction with the TS, and propagation to the heliosheath. We found that in the supersonic solar wind the interaction region between the shocks expands, the shocks weaken and decelerate. The fluctuation amplitudes of the plasma parameters vary with heliocentric distance. The interaction of the pair of shocks with the TS creates a variety of new waves and discontinuities in the heliosheath, which produce a highly variable solar wind flow. The collision of the forward shock with the heliopause causes a reflection of fast magnetosonic waves inside the heliosheath.

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Title: The Heliosphere---Blowing in the Interstellar Wind
Authors: P. C. Frisch

Measurements of the velocity of interstellar HeI inside of the heliosphere have been conducted over the past forty years. These historical data suggest that the ecliptic longitude of the interstellar flow has increased at a rate of about 0.18 degrees per year. Possible astronomical explanations for these short-term variations in the interstellar gas entering the heliosphere are presented.

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 IBEX Reveals a Missing Boundary At the Edge Of the Solar System



For the last few decades, space scientists have generally accepted that the bubble of gas and magnetic fields generated by the sun - known as the heliosphere - moves through space, creating three distinct boundary layers that culminate in an outermost bow shock. This shock is similar to the sonic boom created ahead of a supersonic jet. Earth itself certainly has one of these bow shocks on the sunward side of its magnetic environment, as do most other planets and many stars. A collection of new data from NASA's Interstellar Boundary Explorer (IBEX), however, now indicate that the sun does not have a bow shock.
In a paper appearing online in Science Express on May 10, 2012, scientists compile data from IBEX, NASA's twin Voyager spacecraft, and computer models to show that the heliosphere just isn't moving fast enough to create a bow shock in the tenuous and highly magnetised region in our local part of the galaxy.

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IBEX: Glimpses of the Interstellar Material Beyond our Solar System



A great magnetic bubble surrounds the solar system as it cruises through the galaxy. The sun pumps the inside of the bubble full of solar particles that stream out to the edge until they collide with the material that fills the rest of the galaxy, at a complex boundary called the heliosheath. On the other side of the boundary, electrically charged particles from the galactic wind blow by, but rebound off the heliosheath, never to enter the solar system. Neutral particles, on the other hand, are a different story. They saunter across the boundary as if it weren't there, continuing on another 7.5 billion miles for 30 years until they get caught by the sun's gravity, and sling shot around the star.
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The edge of the solar system is filled with a turbulent sea of magnetic bubbles, astronomers said Thursday.
The finding changes ideas about the distant region and how the rest of the galaxy interacts with the solar system.
The two Voyager spacecraft, which have spent more than three decades travelling toward the outer boundaries of our solar system, found unexpected changes in the magnetic field that extends outward from the Sun. This discovery was made once they reached the heliosheath, as the outer part of the solar system is called.

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IBEX Maps Heliopause





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