page_title: Heliosphere
section_title: Summary
hierarchical_section_title: Heliosphere / Summary
caption_attribution_description: English: All-sky map created using the IBEX spacecraft. This data comes from the IBEX-Hi instrument showing differential flux at 0.9-1.5 keV.
context_page_description: The heliosphere is the vast, bubble-like region of space that surrounds and is created by the Sun. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the Milky Way. Radiation levels inside and outside the heliosphere differ; in particular, the galactic cosmic rays are less abundant inside the heliosphere, so that the planets inside are partly shielded from their impact. The word "heliosphere" is said to have been coined by Alexander J. Dessler, who is credited with first use of the word in scientific literature in 1967. The scientific study of the heliosphere is heliophysics, which includes space weather and space climate.
  Flowing unimpeded through the Solar System for billions of kilometres, the solar wind extends far beyond even the region of Pluto, until it encounters the termination shock, where its motion slows abruptly due to the outside pressure of the interstellar medium.
context_section_description: The Heliosphere is the area under the influence of the Sun; the two major components to determining its edge are the heliospheric magnetic field and the solar wind from 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 113 au (1.69×10¹⁰ km; 1.05×10¹⁰ mi), 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 (1.8×10¹⁰ km; 1.1×10¹⁰ mi), Voyager 1 detected a sudden increase in cosmic rays, an apparent signature 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 122 au (1.83×10¹⁰ km; 1.13×10¹⁰ mi) 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.
  Pioneer 10 was launched in March 1972, and within 10 hours passed by the Moon; over the next 35 years or so the mission would be the first out laying out many firsts of discoveries about the nature of heliosphere as well as Jupiter's impact on it. Pioneer 10 was the first spacecraft to detect sodium and aluminum ions in the Solar Wind, as well as helium in the inner Solar System. In November 1972, Pioneer 10 encountered Jupiter's enormous (compared to Earth) magnetosphere, and would pass in and out of it and heliosphere 17 times charting its interaction with the Solar Wind. Pioneer 10 returned scientific data until March 1997, including data on the Solar wind out to about 67 AU at that time. It was also contacted in 2003, when it was a distance of 7.6 billion miles from Earth (82 AU), but no instrument data about the Solar Wind was returned then.
  Voyager 1 surpassed the radial distance from Sun of Pioneer 10 at 69.4 AU on 17 February 1998, because it was traveling faster gaining about 1.02 AU per year. Pioneer 11, launched a year after Pioneer 10, took similar data as Pioneer out to 44.7 AU in 1995 when that mission was concluded. Pioneer 11 had a similar instrument suite as 10, but also had a Flux-Gate Magnetometer. Pioneer and Voyager spacecraft were on different trajectories, and thus recorded data on the heliosphere in different overa
caption: Energetic neutral atoms map by IBEX. Credit: NASA / Goddard Space Flight Center Scientific Visualization Studio.
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