Using longer exposures and sophisticated processing techniques, scientists have taken extraordinarily high-fidelity pictures of the Sun’s outer atmosphere – what we call the corona – and discovered fine details that have never been detected before.
The Sun is a complex object, and with the soon-to-be-launched Parker Solar Probe we’re on the verge of learning so much more about it. But there’s still a lot we can do with our current technology, as scientists from the Southwest Research Institute (SwRI) have just demonstrated.
The team used the COR-2 coronagraph instrument on NASA’s Solar and Terrestrial Relations Observatory-A (STEREO-A) to study details in the Sun’s outer atmosphere.
This instrument takes images of the atmosphere by using what is known as an occulting disc – a disc placed in front of the lens that blocks out the actual Sun from the image, and therefore the light that would overwhelm the fine details in the plasma of the Sun’s atmosphere.
The corona is extremely hot, much hotter than the inner photosphere’s 5,800 Kelvin, coming in at between 1 and 3 million Kelvin. It’s also the source of solar wind – the constant stream of charged particles that flows out from the Sun in all directions.
When measurements of the solar wind are taken near Earth, the magnetic fields embedded therein are complex and interwoven, but it’s unclear when this turbulence occurs.
“In deep space, the solar wind is turbulent and gusty,” says solar physicist Craig DeForest of the SwRI.
“But how did it get that way? Did it leave the Sun smooth, and become turbulent as it crossed the solar system, or are the gusts telling us about the Sun itself?”
If the turbulence was occurring at the source of the solar wind – the Sun – then we should have been able to see complex structures in the corona as the cause of it, but previous observations showed no such structures.
Instead, they showed the corona as a smooth, laminar structure. Except, as it turns out, that wasn’t the case. The structures were there, but we hadn’t been able to obtain a high enough image resolution to see them.