The sun’s effects are felt far and wide. Solar wind blows across the first planet to the chunks of ice beyond Pluto. But the solar wind’s structure isn’t always the same. Scientists are getting their first full look at the solar wind thanks to NASA’s Solar Terrestrial Relations Observatory, or STEREO.
“Now we have a global picture of solar wind evolution,” says Nicholeen Viall, a co-author of a new paper and a solar scientist at NASA Goddard.
What does this picture look like? Solar wind’s structure changes as it blows away from the sun. To understand this, we need to understand what the sun is made of.
The sun isn’t just a ball of fire in space. It’s made up of plasma. This mass of charged particles (positive and negative charged particles separated by the sun’s scorching temperatures) constantly travels outward from the sun along strong magnetic field lines.
When the plasma travels past the sun’s atmosphere (the corona) it changes big time. It goes from structured rays held tightly together by strong magnetic fields to a more turbulent ‘wind.’
What’s going on? The sun’s magnetic grip over the solar wind lossens. The magnetic control drops faster than the pressure of the material inside the plasma. With the strong magnetic fields no longer influencing it as much, the solar wind’s structure breaks down and fans out.
NASA likens the effect to water coming from a squirt gun. The stream of water starts out in a tight structure, but as it travels it breaks up into droplets. New images captured by STEREO show a similar transition in structure.
Scientists hypothesized this was going on before the new study. But seeing it in action wasn’t possible until now. Distance (the sun sits 20 million miles away) wasn’t the only issue. The solar wind is already tough to see. In order to see the transition zone, scientists needed to get rid of all the other sources of light in the images. That means background stars. Stray light from the sun. Hell, even specks of dust.
This isn’t something you can just do in Photoshop. The team created an algorithm that removed all the other sources of light, but kept the solar wind. The results (seen above) are stunning.
This week’s study places a couple more pieces into the sun puzzle. The more we know, the better models scientists can develop to predict space weather on Earth. It helps it makes for a remarkable image.
NASA doesn’t plan to stop staring at the sun anytime soon. In 2018, the space agency will launch the Solar Probe Plus mission and make history. It will be the first spacecraft to visit the sun. Solar Probe Plus will fly into the sun’s corona and take measurements of the near-Sun environment.
Why is the temperature at the corona so much hotter than the photosphere? What are the exact mechanics driving the solar wind? Those questions and more will answered when the spacecraft makes its first close approach to the sun in late 2024.