page_title: Heliosphere
section_title: Timeline of exploration & detection
hierarchical_section_title: Heliosphere / Observational methods / Timeline of exploration & detection
caption_attribution_description: English: Parker Solar Probe artist rendering Artist’s concept of the Parker Solar Probe spacecraft approaching the sun. Launching in 2018, Parker Solar Probe will provide new data on solar activity and make critical contributions to our ability to forecast major space-weather events that impact life on Earth.
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: 1904 : The Potsdam Great Refractor with a spectrograph detects interstellar medium. The binary star Mintaka in Orionis determined to have the element calcium in the intervening space.
  January 1959: Luna 1 becomes the first spacecraft to observe the solar wind.
  1962: Mariner 2 detects the solar wind.
  1972–1973: Pioneer 10 becomes the first spacecraft to explore the heliosphere past Mars, flying by Jupiter on 4 December 1973 and continuing to return solar wind data out to a distance of 67 AU.
  February 1992: After flying by Jupiter, the Ulysses spacecraft becomes the first to explore the mid and high latitudes of the heliosphere.
  1992: Pioneer and Voyager probes detected Ly-α radiation resonantly scattered by heliospheric hydrogen.
  2004: Voyager 1 becomes the first spacecraft to reach the termination shock.
  2005: SOHO observations of the solar wind show that the shape of the heliosphere is not axisymmetrical, but distorted, very likely under the effect of the local galactic magnetic field.
  2009: IBEX project scientists discover and map a ribbon-shaped region of intense energetic neutral atom emission. These neutral atoms are thought to be originating from the heliopause.
  October 2009: the heliosphere may be bubble, not comet shaped.
  October 2010: significant changes were detected in the ribbon after 6 months, based on the second set of IBEX observations.
  May 2012: IBEX data implies there is probably not a bow "shock".
  June 2012: At 119 AU, Voyager 1 detected an increase in cosmic rays.
  25 August 2012: Voyager 1 crosses the heliopause, becoming the first human-made object to depart the heliosphere.
  August 2018: long-term studies about the hydrogen wall by the New Horizons spacecraft confirmed results first detected in 1992 by the two Voyager spacecraft.
  5 November 2018: Voyager 2 crosses the heliopause, departing the heliosphere.
caption: Parker Solar Probe, launched in 2018 explores the region near the Sun
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