Solar wind isn't really wind. Wind is moving air, and there's no air in space. In preparation for a NASA probe heading towards the sun to study the still-mysterious phenomena, an Italian space physics Ph.D. student has gone back and analyzed some of the Agency's previous looks at solar wind and found himself on a historic research trail that dated back to the 1970s, studying giant radioactive blobs from the sun.
Some background: last year, NASA launched the Parker Space Probe, which in 2025 should become the closest man-made object to the sun in history. The previous record was set by Helios 2, one in a pair of probes NASA launched in 1974, which reached its point of study in 1976.
Solar wind is a stream of charged particles that blows constantly from the sun into Earth's magnetosphere. While the magnetosphere shields Earth from the harmful radiation within these particles, giant blobs of them can create disturbances that interfere with satellites and communications signals.
Di Matteo, who studies at the University of L'Aquila in Italy, began analyzing Helios data as part of his own research leading up to the Parker's meeting with the sun, hoping he could trace the blobs route from the star to Earth. "You can look at spacecraft data all you want, but if you can connect it back to where it came from on the Sun, it tells a more complete story," says Samantha Wallace, a study collaborator with Di Matteo and a physics Ph.D. student at the University of New Mexico in Albuquerque, in a .
Both Di Matteo and Wallace were trying to to link magnetic maps of the solar surface to Helios' observation, a difficult task considering the data speaks different languages in terms of older and modern data conventions.
But while they expected to find alternating patterns of solar wind, they found consistency. Remarkable consistency. Troubling, in fact.
"That was a red flag," says NASA solar scientist Nicholeen Viall, who advised Di Matteo during his time using NASA facilities in Maryland. "The actual solar wind doesn't have such precise, clean periodicities. Usually when you get such a precise frequency, it means some instrument effect is going on."
That meant going back to the source. Unfortunately, the people who built and worked with Helios in the 70s were not around. Di Matteo was left doing what everyone else does when they can't find something: lots of Googling. Eventually he was able to find the culprit of the faulty data: the Helios spacecraft itself, which would alternate between two different instruments that would each measure certain solar wind properties in different way. The data they were looking at was unusually clean because it was taken as the spacecraft was alternating between instruments.
Removing segments of data from these transitional periods was able to clear matters up considerably. Di Matteo and his fellow scientists were able to find five instances in which . Helios happened to catch trains of blobs. For the first time, Di Matteo and other scientists were able to say definitively that these blobs are hotter and denser than the typical solar wind.
There are still many questions left unanswered: if they travel in 90-minute intervals or in spurts, and how much they vary between themselves. The Parker Space Probe will hopefully be able to answer a lot of these questions. "This is one of those studies that brought up more questions than we answered, but that's perfect for Parker Solar Probe," Viall said.
The Parker team is grateful for Di Matteo's work. "This is going to be very helpful," says Aleida Higginson, the mission's deputy project scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. "If you want to even begin to understand things you've never seen before, you need to know what we've measured before and have a solid scientific interpretation for it."
The Parker Space Probe just performed its second solar flyby yesterday, bringing it 15 million miles from the Sun. That already cuts Helios' record in half.