- Boundary between upper solar atmosphere and solar wind is directly observed.
- Image processing algorithms create first movies of solar wind from streaming satellite images.
- New understanding will aid space exploration.
Until recently, the solar wind was virtually an article of faith. But in the summer of 2016 scientists were able to see it for the first time.
Know your sun
Moving from the center outward, our dear sun has a core, radiative and convective zones, a photosphere, a chromosphere, and a corona — the sun’s atmosphere. The corona extends about a million miles into space, and is what we see when we look into the sky, or when we drew the sun as children.
As solar plasma escapes from the sun, the sun’s gravitational hold weakens with distance, eventually reaching a transition point between the corona and the solar wind.
At about 20 million miles out from the sun, solar particles – some streaming at a million miles per hour – gain turbulence as the sun’s gravitational hold loosens. (Think of how a stream of water loses its force and focus the further away it gets from the nozzle of your garden hose.)
This turbulent blast of plasma extends in all directions from the sun and extends to the outer reaches of our solar system. Scientists refer to this ‘bubble’ as the heliosphere. We refer to it as home.
Reporting in The Astrophysical Journal, scientists offer a nuanced definition of our sun with visual evidence to back it up.
Turns out, the sun is neither a hard ball in space nor an immense raging ball of fire.
Rather, it is a mass of particles and magnetic fields extending outward well beyond the sun’s actual surface. This atmosphere pushes outward throughout our solar system, engulfing all the planets in the solar wind.
To create the first movie of this wind, scientists started with images taken over a 15-day interval in late December of 2008 from the Heliospheric Imager in the SECCHI suite onboard NASA's Solar Terrestrial Relations Observatory (STEREO).
Then, using novel image processing techniques including background brightness suppression, scientists were able to discern the boundary between the upper corona and the solar wind.
No longer mere theory or an an article of faith, astrophysicists can now see the solar wind with their own eyes.
Imaging the solar wind is significant because it identifies a shift in plasma texture as it flows away from the sun.
Objects placed in this upper extreme of the solar corona (say, a satellite, space ship, or a person) will be safer and more productive with this better understanding of the solar wind.
And the images look pretty cool, too.