Heliosphere: The heliosphere is a region of space dominated by the Sun, a sort of bubble of charged particles in the space surrounding the Solar System, "blown" into the interstellar medium (the hydrogen and helium gas that permeates the galaxy) by the solar wind. Although electrically neutral atoms from the extra-solar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself. The Sun's Corona is so hot that particles reach escape velocity, streaming outwards at 300 to 800 km/s (1 to 2 million mph) producing the solar wind. For the first ten billion kilometers of its radius[citation needed], the solar wind travels at over 1,000,000 km/h. As it begins to interact with the interstellar medium, it slows down before finally ceasing altogether. The point where the solar wind begins to slow is called the termination shock; the solar wind continues to slow as it passes through the heliosheath leading to a boundary called the heliopause where the interstellar medium and solar wind pressures balance. The termination shock was successfully detected by both Voyager 1 in 2004, and Voyager 2 in 2007. As the sun is moving through space it was assumed that beyond the heliopause there might be a bow shock, similar to a bow wave created as a ship passes through water, where the interstellar medium collides with the heliosphere. However, data from the Interstellar Boundary Explorer suggests that the velocity of the Sun through the interstellar medium is too low for a bow shock to form. Also, Cassini and IBEX data challenged the "heliotail" theory in 2009. Voyager data led to a new theory that the heliosheath has "magnetic bubbles" and a stagnation zone. The 'stagnation region' within the heliosheath, starting around 113 AU, was detected by Voyager 1 in 2010. There the solar wind velocity drops to zero, the magnetic field intensity doubles, and high-energy electrons from the galaxy increase 100-fold. Starting in May 2012 at 120 AU, Voyager 1 detected a sudden increase in cosmic rays, an apparent signature of approach to the heliopause. In December 2012 NASA announced that in late August 2012 Voyager 1, at about 122 AU from the Sun, entered a new region they called the "magnetic highway", an area still under the influence of the Sun, but with some dramatic differences. ___________________________ Héliosphère: L'héliosphère est une zone en forme de bulle allongée dans l'espace, engendrée par les vents solaires. Sa limite est l'héliopause, qui délimite la zone d'influence des vents solaires, lorsqu'ils rencontrent le milieu interstellaire. Le vent solaire consiste en la projection de particules atomiques (essentiellement protons et électrons) par la haute atmosphère de notre étoile, le Soleil. Ce plasma impose une pression (une sorte de souffle) vers l'extérieur du système solaire et repousse le flux de particules similaires mais provenant de l'espace lointain. La forme de la bulle ainsi produite n'est que très approximativement sphérique et reste sujette à controverses scientifiques, mais les éléments principaux en sont relativement bien définis : une forme allongée produite par le déplacement du Soleil, une forme spiralée produite par la rotation du Soleil, diverses déformations provenant de l'influence des champs magnétiques solaires et planétaires qui influencent fortement la trajectoire des particules chargées qui constituent le vent solaire. En particulier, il est considéré comme très probable que la limite de l'héliosphère, l'héliopause, soit très fluctuante et largement influençable par des facteurs internes comme externes (les éruptions solaires, par exemple).