the Sun. Three major sections from the beginning of the heliosphere to its edge are the termination shock, the heliosheath, and the heliopause. Five spacecraft have returned much of the data about its furthest reaches, including Pioneer 10 (1972–1997; data to 67 AU), Pioneer 11 (1973–1995; 44 AU), Voyager 1 and Voyager 2 (launched 1977, ongoing), and New Horizons (launched 2006). A type of particle called an energetic neutral atom (ENA) has also been observed to have been produced from its edges. Except for regions near obstacles such as planets or comets, the heliosphere is dominated by material emanating from the Sun, although cosmic rays, fast-moving neutral atoms, and cosmic dust can penetrate the heliosphere from the outside. Originating at the extremely hot surface of the corona, solar wind particles reach escape velocity, streaming outwards at 300 to 800 km/s (671 thousand to 1.79 million mph or 1 to 2.9 million km/h). As it begins to interact with the interstellar medium, its velocity slows to a stop. The point where the solar wind becomes slower than the speed of sound 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 traversed by Voyager 1 in 2004, and Voyager 2 in 2007. It was thought that beyond the heliopause there was a bow shock, but data from Interstellar Boundary Explorer suggested the velocity of the Sun through the interstellar medium is too low for it to form. It may be a more gentle "bow wave". Voyager data led to a new theory that the heliosheath has "magnetic bubbles" and a stagnation zone. Also, there were reports of a "stagnation region" within the heliosheath, starting around , 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 , Voyager 1 detected a sudden increase in cosmic rays, an apparent sign of approach to the heliopause. In the summer of 2013, NASA announced that Voyager 1 had reached interstellar space as of 25 August 2012. In December 2012, NASA announced that in late August 2012, Voyager 1, at about from the Sun, entered a new region they called the "magnetic highway", an area still