NASA scientists have for the first time imaged the edge of the Sun, enabling them to describe the mysterious origins of solar wind.
The details of the transition from defined rays in the corona, the Sun’s upper atmosphere, to the solar wind have been, until now, a mystery.
Now, using NASA’s Solar Terrestrial Relations Observatory, or STEREO, scientists have for the first time imaged the edge of the Sun and described that transition, where the solar wind starts.
The Sun and its atmosphere are made of plasma – a mix of positively and negatively charged particles which have separated at extremely high temperatures, that both carries and travels along magnetic field lines.
Material from the corona streams out into space, filling the solar system with the solar wind.
However, scientists found that as the plasma travels further away from the Sun, things change: The Sun begins to lose magnetic control, forming the boundary that defines the outer corona – the very edge of the Sun.
Twenty million miles from the Sun, the solar wind plasma is tenuous, and contains free-floating electrons which scatter sunlight. This means they can be seen, but they are very faint and require careful processing.