The Sun’s surface and atmosphere are made of plasma – a mix of positively and negatively charged particles which have separated at extremely high temperatures and travel along magnetic field lines. Material from the corona streams out into space, filling the Solar System with the solar wind. But as the plasma travels further away, the Sun begins to lose magnetic control, forming the boundary that defines the outer corona – the very edge of the Sun. As it goes farther from the Sun, the magnetic field strength drops faster than the pressure of the material does. Eventually, the material starts to act more like a gas, and less like magnetically structured plasma. It eventually disintegrates, just like a spurt of water would break up into droplets, then smaller drops and eventually a fine, misty spray. The images in this study capture that disintegration.
In order to resolve the transition zone, scientists had to separate the faint features of the solar wind from the background noise and light sources over 100 times brighter: the background stars, stray light from the Sun itself and even dust in the inner solar system. Such observations from the STEREO mission help inform the next generation of Sun-watchers. In 2018, NASA is scheduled to launch the Solar Probe Plus mission, which will fly into the Sun’s corona, collecting more valuable information on the origin and evolution of the solar wind.
Reference: "Fading coronal structure and the onset of turbulence in the young solar wind" - C. E. DeForest, W. H. Matthaeus, N. M. Viall, and S. R. Cranmer - Published September 1, 2016 -The American Astronomical Society - DOI: 10.3847/0004-637X/828/2/66
Source Reference: http://thewatchers.adorraeli.com/2016/09/03/origins-of-solar-wind-revealed/
Credit for featured image at top of page: processed STEREO data of the solar wind. Data credit: Craig DeForest, SwRI