Heliosphere
As part of the interplanetary magnetic field, the heliosphere shields the Solar System from significant amounts of cosmic ionizing radiation; uncharged gamma rays are, however, not affected.The heliosphere is thought to change significantly over the course of millions of years due to extrasolar effects such as closer supernovas or the traversing interstellar medium of different densities.Changes in the solar wind, however, more strongly alter the fluctuating position of the boundaries on short timescales (hours to a few years).The solar wind plasma which is moving roughly "upstream" (in the same direction as the Sun's motion through the galaxy) is compressed into a nearly-spherical form, whereas the plasma moving "downstream" (opposite the Sun's motion) flows out for a much greater distance before giving way to the ISM, defining the long, trailing shape of the heliotail.Because the Sun rotates once approximately every 25 days, the heliospheric magnetic field[11] transported by the solar wind gets wrapped into a spiral.This takes place in several stages: The termination shock is the point in the heliosphere where the solar wind slows down to subsonic speed (relative to the Sun) because of interactions with the local interstellar medium.Other termination shocks can be seen in terrestrial systems; perhaps the easiest may be seen by simply running a water tap into a sink creating a hydraulic jump.Evidence presented at a meeting of the American Geophysical Union in May 2005 by Ed Stone suggests that the Voyager 1 spacecraft passed the termination shock in December 2004, when it was about 94 AU from the Sun, by virtue of the change in magnetic readings taken from the craft.A proposed model hypothesizes that the heliosheath is shaped like the coma of a comet, and trails several times that distance in the direction opposite to the Sun's path through space.[26] Voyager project scientists have determined that the heliosheath is not "smooth" – it is rather a "foamy zone" filled with magnetic bubbles, each about 1 AU wide.At about 122 AU, the spacecraft entered a new region that Voyager project scientists called the "magnetic highway", an area still under the influence of the Sun but with some dramatic differences.The crossing of the heliopause should be signaled by a sharp drop in the temperature of solar wind-charged particles,[31] a change in the direction of the magnetic field, and an increase in the number of galactic cosmic rays.The tail is a region where the Sun's solar wind slows down and ultimately escapes the heliosphere, slowly evaporating because of charge exchange.[51] Another hypothesis suggests that the heliopause could be smaller on the side of the Solar System facing the Sun's orbital motion through the galaxy.Initial results (October 2009) from IBEX suggest that previous assumptions are insufficiently cognizant of the true complexities of the heliopause.Rather than a comet-like shape, the heliosphere appears to be bubble-shaped according to data from Cassini's Ion and Neutral Camera (MIMI / INCA).Rather than being dominated by the collisions between the solar wind and the interstellar medium, the INCA (ENA) maps suggest that the interaction is controlled more by particle pressure and magnetic field energy density.[13][58] Initial data from Interstellar Boundary Explorer (IBEX), launched in October 2008,[59] revealed a previously unpredicted "very narrow ribbon that is two to three times brighter than anything else in the sky."[14] Initial interpretations suggest that "the interstellar environment has far more influence on structuring the heliosphere than anyone previously believed"[60] "No one knows what is creating the ENA (energetic neutral atoms) ribbon, ..."[61] "The IBEX results are truly remarkable![51] Examples of missions that have or continue to collect data related to the heliosphere include: During a total eclipse the high-temperature corona can be more readily observed from Earth solar observatories.[29] 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 sign of approach to the heliopause.[66] In November 1972, Pioneer 10 encountered Jupiter's enormous (compared to Earth) magnetosphere and would pass in and out of it and its heliosphere 17 times charting its interaction with the solar wind.[74] Upon passing the heliopause, Voyager 2's Plasma Science Experiment (PLS) observed a sharp decline in the speed of solar wind particles on 5 November and there has been no sign of it since.NASA is also preparing an additional mission, Interstellar Mapping and Acceleration Probe (IMAP) which is due to launch in 2025 to capitalize on Voyager's observations.
Stellar-wind bubbleinterstellar mediumVoyager spacecrafttermination shockmagnetosphereastrosphereatmosphericplasmasolar windMilky Wayinterplanetary magnetic fieldSolar Systemcosmicionizing radiationgamma raysAlexander J. Desslerheliophysicsspace weatherspace climateregion of Plutopressureheliosheathheliopauseastronomical unitsVoyager programVoyager 1densityVoyager 2supernovasInner Solar Systemultravioletsolar cycleMerav OpherInterplanetary mediumionizedsolar coronamagnetic fieldrotatesheliospheric magnetic fieldgeomagnetic stormsHeliospheric current sheetNeptunesupersonicshock wavesubsonicGalactic CenterTermination Shock (novel)compressionhydraulic jumpwave speedAmerican Geophysical UnionEd Stonewindwardmagnetic reconnectionsolar magnetic fieldstellar windsgalactic cosmic raysflux tubessuborbitalSHIELDSInterstellar Boundary Explorerenergetic neutral atomsCassiniEnergetic neutral atomLocal Interstellar CloudLocal BubbleOrion ArmMilky Way GalaxyHydrogen (disambiguation)New HorizonsBow shockUlyssesPioneer HspacecraftPioneer 10Pioneer 11List of heliophysics missionsSolar Anomalous and Magnetospheric Particle ExplorerSolar and Heliospheric ObservatorySolar Dynamics ObservatorySTEREOUlysses spacecraftParker Solar ProbeSolar Wind Composition ExperimentMcMath–Pierce solar telescopeGREGOR Solar TelescopeBig Bear Solar ObservatoryGoddard Space Flight Centerregionsplanetscosmic raysfast-moving neutral atomscosmic dustcoronaescape velocityinterstellar spaceOort CloudPotsdam Great RefractorspectrographMintakaLuna 1Mariner 2Ly-α radiationaxisymmetricalCoronal mass ejectionFermi glowBibcodeAstronomy Picture of the DayJet Propulsion LaboratoryNew ScientistThe Planetary SocietyNatureNASA.govAmerican Astronomical SocietyGeophysical Research LettersLive ScienceScienceWayback MachineThe SunInternal structureRadiative zoneTachoclineConvection zoneAtmospherePhotosphereSupergranulation