Heliosphere

The heliosphere is the <a href="/facts/Magnetosphere/BXzgPoPy">magnetosphere</a>, <a href="/facts/Astrosphere/hjIcT4u0">astrosphere</a>, and outermost <a href="/facts/Atmosphere/oUpLaGRF">atmospheric</a> layer of the <a href="/facts/Sun/CadPCVHh">Sun</a>. It takes the shape of a vast, tailed bubble-like <a href="/facts/Outer_space/R3LRKyFs">region of space</a>. In plasma physics terms, it is the cavity formed by the Sun in the surrounding <a href="/facts/Interstellar_medium/mokU0WEz">interstellar medium</a>. The "bubble" of the heliosphere is continuously "inflated" by <a href="/facts/Plasma_(physics)/1d3btMVU">plasma</a> originating from the Sun, known as the <a href="/facts/Solar_wind/BvuB3dT8">solar wind</a>. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the <a href="/facts/Milky_Way/ulF6lccN">Milky Way</a>. As part of the <a href="/facts/Interplanetary_magnetic_field/AvWnxtbQ">interplanetary magnetic field</a>, the heliosphere shields the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a> from significant amounts of <a href="/facts/Cosmic_ray/uxCVdTKd">cosmic</a> <a href="/facts/Ionizing_radiation/vw0d9GaT">ionizing radiation</a>; uncharged <a href="/facts/Gamma_ray/5Drf913J">gamma rays</a> are, however, not affected. Its name was likely coined by <a href="/facts/Alexander_J._Dessler/qUh3UT3U">Alexander J. Dessler</a>, who is credited with the first use of the word in the scientific literature in 1967. The scientific study of the heliosphere is <a href="/facts/Heliophysics/QW7vrybp">heliophysics</a>, which includes <a href="/facts/Space_weather/FfwUCv2G">space weather</a> and <a href="/facts/Space_climate/UonASX9I">space climate</a>.
Flowing unimpeded through the Solar System for billions of kilometers, the solar wind extends far beyond even the <a href="/facts/Kuiper_Belt/IvLzYp5P">region of Pluto</a> until it encounters the "<a href="/facts/Termination_shock/Yc9ToWbA">termination shock</a>", where its motion slows abruptly due to the outside <a href="/facts/Pressure/eyc37GRG">pressure</a> of the interstellar medium. The "<a href="/facts/Heliosheath/Yc9ToWbA">heliosheath</a>" is a broad transitional region between the termination shock and the heliosphere's outmost edge, the "<a href="/facts/Heliopause_(astronomy)/Yc9ToWbA">heliopause</a>". The overall shape of the heliosphere resembles that of a <a href="/facts/Comet/w34utQCd">comet</a>, being roughly spherical on one side to around 100 <a href="/facts/Astronomical_unit/gjsbu5xU">astronomical units</a> (AU), and on the other side being tail shaped, known as the "heliotail", trailing for several thousands of AUs.
Two <a href="/facts/Voyager_program/cPm6qnNx">Voyager program</a> spacecraft explored the outer reaches of the heliosphere, passing through the termination shock and the heliosheath. <a href="/facts/Voyager_1/39jCxR9I">Voyager 1</a> encountered the heliopause on 25 August 2012, when the spacecraft measured a forty-fold sudden increase in plasma <a href="/facts/Density/92p6hh9I">density</a>. <a href="/facts/Voyager_2/9FAEaHUr">Voyager 2</a> traversed the heliopause on 5 November 2018. Because the heliopause <a href="/facts/Solar_System/QIcLSazQ">marks the boundary</a> between matter originating from the Sun and matter originating from the rest of the galaxy, spacecraft that depart the heliosphere (such as the two Voyagers) are in <a href="/facts/Outer_space/R3LRKyFs">interstellar space</a>.

Heliosphere open-in-new

Heliosphere