Heliosphere

The heliosphere is the long-range interplanetary field around the sun in which the solar wind with its entrained magnetic fields is effective. In this area of the solar system the particle of the sun displaces the interstellar matter up out of the heliopause. For electrically neutral atoms from the interstellar medium is the ability to penetrate deep into the heliosphere. Besides the few particles that do that, comes almost the entire amount of particles in the heliosphere of the sun.

• 3.1 Voyager Program
• 3.2 Solar Terrestrial Relations Observatory (STEREO)
• 3.3 Interstellar Boundary Explorer ( IBEX )

Solar wind

The solar wind is a stream of particles of electrically charged particles, so-called plasma, consisting of protons, electrons and alpha particles. The origin of the solar wind, the outer layers of the sun. It consists of two different components: the fast solar wind (german high-speed streams) and the slow solar wind (English low-speed streams). During the fast solar wind mainly in coronal holes ( cf. coronal mass ejection ) emerges, whose incidence is increasing in the polar regions, which emit other regions of the slow solar wind. By the rotation of the sun produces a rotating magnetic field, which changes its polarity, and produces electrical currents. This is especially evident in the vicinity of the ecliptic as heliospheric current sheet (English Heliospheric current sheet ).

By the radiation pressure of the solar wind that has thoroughly cleaned the interior region of the heliosphere from interstellar gas by simply pushing back this into the interstellar medium or entrains. At a distance of 1 AU from the Sun the number density of the solar wind is out of coronal mass ejections from one to ten million particles per cubic meter. Due to the particle mass ejections in the solar wind can at this distance to increase by more than a hundredfold.

Construction

While the sun near region is dominated by the solar wind itself and the heliospheric current sheet, show up from a distance of about 100 AU on the basis of the solar wind interaction with the interstellar gas other phenomena. Since (about 350-400 km / s, fast solar wind about 800-900 km / s slower solar wind ) move away from the solar wind with a speed of several hundred kilometers per second from the sun, there must be limits at which the solar wind is decelerated by the interstellar medium, and for consistency with low velocities in the interstellar medium.

This is done in several phases: the first boundary of the solar system is the termination shock, where the strong influence of the solar wind ends. Here the flow of particles is stopped under the prevailing plasma sound speed and possible disturbances in the plasma, which propagate with the speed of sound, are now, unlike before, affect the decelerated solar wind. The then this section will be called Heliosheath and can be disturbed by the interstellar medium, but here is still the solar wind, the dominating feature, which decreases more and more with increasing distance from the Sun. The last limit at which the solar wind has no material impact on the interstellar gas, is called the heliopause and describes the outermost boundary of the heliosphere. This is at a distance of around 110-150 AE suspected, these data strongly depend on the crossed by the sun at the moment the interstellar medium and the interstellar magnetic field, as they can change the heliosphere greatly in their shape and spread. So the heliosphere has by action of the impinging thereon interstellar matter, caused by the natural movement of the sun, an indented shape similar to the shape of the earth's magnetic field, which is pushed by the solar wind.

Termination shock

The termination shock referred to one of the outer limits of the solar system. The border is where the particles of the solar wind are decelerated and heated abruptly by the interaction with the interstellar gas. Compressed due to the deceleration of about 350 km / s to about 130 km / s at low latitudes and the further subsequent flow of matter and heats the medium of the solar wind. Measurements showed, however, that the temperature does not increase so much by far as it predicted models. It is believed that the energy part is excreted in the acceleration of the material encountered. This could for example be electrically neutral hydrogen atoms at a speed of about 25 km / s entered the Heliosheath and advanced to the termination shock.

Up to this point, the solar wind moves unaffected by the room, since disturbances of the density and the pressure in the plasma more slowly moving than the flow itself The rate of density perturbations can be interpreted as the speed of sound as a propagation of acoustic waves and of gases such low density as in the case of the solar wind is possible. At the point of termination shock, the flow rate drops below the assigned speed of sound, so that for the first time the influence of the interstellar medium occurs. As a result, there is still a significant increase of the magnetic field.

Heliosheath

Outside of the termination shock, the Heliosheath is ( German about: sun wrapping ), in the region continue to occur solar wind, but now with a reduced flow rate at higher density and temperature. In this region, solar wind particles and the local interstellar medium mix. This zone is probably several 10 AU in size and extends opposite to the proper motion of the sun in the interstellar space. So it can be thick in the direction of self-motion of the sun only 10 AU, while it can have up to 100 AU in the opposite direction, a thickness. Compared with that of the other zones of the solar system, the Heliosheath is thus between the sun closer Kuiper belt and the Oort cloud the very outside. The outer edge of Heliosheath is the heliopause.

Heliopause

The theoretical limit of the last substantive effect of the solar wind meets the interstellar gas is called the heliopause, because there ends all direct solar exposure. Here, the particles of the solar wind mixed with the interstellar gas and have no apparent stand-out flow direction as compared with the gas surrounding the heliosphere.

Research

Voyager Program

The exploration with probes proves to be difficult because the distances are so great that a probe would take around 30 years to reach a distance of 100 AU from the sun. The only built by man-made objects that have ever penetrated the Heliosheath, so have passed the termination shock, the two probes of the Voyager program are: Voyager 1 and Voyager 2 Thus, the space probe Voyager 1 reached the termination shock on 16 December 2004 AE at 94 distance from the Sun. Voyager 2, however, reached on 30 August 2007 the termination shock even at 84 AU distance. Viewed from Earth, Voyager 1 is located in the constellation Ophiuchus, Voyager 2 in the constellation telescope. Explains Edward Stone of the Goddard Space Flight Center of NASA, the different distances so that the interstellar magnetic field apparently at the point at which Voyager 2 is stronger than in other places.

Also was demonstrated by Voyager 2, that the termination shock is no consistent hard limit, but a dynamic event that is similar to the surf behaves on a beach. So there are density fluctuations in the solar wind, coronal mass ejections caused by or superposition of fast and slow solar winds that are similar to the waves in the sea and thus further extend beyond the Heliosheath. The rotation of the sun, in the exact differential rotation and the large distance from the sun big jumps in the absolute distance can thus be possible from the sun at relatively short intervals. Voyager 2 passed the termination shock within a few days five times before it was finally passed through on August 30, 2007.

In addition, Voyager 2 sent data to the temperature in the Heliosheath, immediately after the termination shock. This was an average of around 180,000 Kelvin far lower than models predicted that emanated from a few million Kelvin. The kinetic energy will not be fully converted into heat, but go to the ionization of the particles encountered there, which would explain the lower temperature. This has been demonstrated indirectly by the Solar Terrestrial Relations Observatory.

Solar Terrestrial Relations Observatory (STEREO)

Actually designed to study the Earth's magnetosphere in conjunction with outbreaks of the Sun, the Solar Terrestrial Relations Observatory detected energetic neutral atoms of interstellar gas from the same direction in which the sun moves in the interstellar medium. According to Robert Lin of the University of California at Berkeley, this is "a new kind of astronomical observations ", especially since the region of Heliosheath can not be studied by normal telescopes. So is the intensity of the detected atoms from the direction in which the sun moves, much larger than in other regions ( see picture). Its origins are energetic ions that have lost in the region of the termination shock their charge to atoms of the interstellar matter and now be able to freely move in the magnetic field of the sun.

In correlation with the measurement results from Voyager 2, which provided a lower temperature than expected, it can be safely said that the energy of the solar wind goes in the ionization of atoms encountered. About 70 percent of the energy of the solar wind, which is exactly the amount that does not pass in the increase of temperature, go to the ionization, which were detected by the instruments of the Solar Terrestrial Relations Observatory.

Interstellar Boundary Explorer ( IBEX )

The research satellite Interstellar Boundary Explorer ( to German as: explorer of the interstellar boundary), which was launched into Earth orbit on 19 October 2008, a Pegasus -XL launch vehicle, the first vehicle dedicated solely to map the neutral atoms from the fields the termination shock has been started. It is located in an extremely eccentric orbit around the earth and has two instruments for the detection of energetic neutral atoms: IBEX -Hi for the high-energy and IBEX -Lo for low-energy particles. Within a year, IBEX will have mapped the entire sky.

Bow Shock

As a bow shock is referred to the effects of density variations in the interstellar medium due to the action of the heliosphere meets the interstellar gas. Owing to the motion of the sun through the dormant compared to the sun's motion gas meets incessantly interstellar matter in the heliosphere. This increases the pressure in the frontal region, thus, similar to a bow wave of a ship, a density wave forms. According to the latest research results, the sun moves so slowly through the interstellar gas, that there is no shock wave.

Due to the compression of the interstellar medium heats it, which is detectable by infrared telescopes. Thus appeared around the star R Hydrae in the photographs from the Spitzer Space Telescope, a marked bow shock ( see Figure 1). To see on the second picture is a bow shock caused by a stream of material, which meets on a star in the constellation Orion. The stellar stream of particles emanating from the star, meets the flowing gas on the star and it forms a good bow wave to be seen. Although Bow Shocks are found in probably every star, it does not show up as clearly as in the example at the star in Orion, but are only visible in the infrared.

Solar magnetosphere

There are theories that the solar system comprehensive magnetosphere is formed by the solar wind, which protects the solar system from cosmic radiation. The movement of the sun in the interstellar space, specifically in the Local Bubble, consisting of two components: on the one of neutral hydrogen with a density from 0.05 to 0.07 atoms per cubic centimeter, on the other hand of a very thin and hot plasma having a density from 0.001 to 0.005 atoms per cubic centimeter and a temperature of 1.4 million degrees Kelvin, the Helio sphere has a relatively large extent. The sun would pass through an area with a much higher density, such as a hydrogen cloud, the heliosphere could be pushed back to the front on. Theoretically, it is possible that dense molecular clouds push back the heliosphere in the areas inside Earth's orbit, and the Earth would thus exposed to the cosmic radiation. This circumstance, he would have ever occurred in the 4.5 billion years ago during the existence of the solar system, could be detected by analysis of sediments. However, there is no evidence that the sun has passed through a molecular cloud in her life span. Similarly, it is not expected that the sun will immerse you in the next million years in a region with higher density.