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When Simone Di Matteo first discovered the trends in her data, it sounded too good to be true. "It's too perfect!" Di Matteo, a doctorate in physics from the student space at the University of L'Aquila in Italy, recalled his thought. "It can not be real." And it was not, he would find out soon.
Di Matteo was looking for long trains of massive droplets – like the bubbles of another world, but 50 to 500 times larger than the Earth – in the solar wind. The solar wind, whose origins are not yet well understood, is the flow of charged particles that constantly blows from the sun. The Earth's magnetic field, called the magnetosphere, protects our planet from the shock of its radiation. However, when giant bursts of solar wind collide with the magnetosphere, they can trigger disturbances that interfere with satellites and daily communications signals.
In his research, Di Matteo was reviewing the archival data of two NASA German Helios spacecraft, launched in 1974 and 1976 to study the Sun. But it was 45-year-old data that he had never worked with before. The impeccable wave-shaped patterns he had originally found suggested that something was misguiding him.
It was only when he discovered and eliminated these false patterns that Di Matteo found exactly what he was looking for: streaks of stains covered with drops that came out of the sun every 90 minutes or so. Scientists have published their findings in JGR Space Physics February 21, 2019. They think that the drops could illuminate the beginnings of the solar wind. Whatever the process that sends the solar wind of the Sun, it must leave signatures on the drops.
Make way for a new science
Di Matteo's research marks the beginning of a project undertaken by NASA scientists in anticipation of the first data from NASA's Parker Solar Probe mission, launched in 2018. Over the next seven years, Parker will go through a unexplored territory, reaching 4 million miles. of the sun. Before Parker, the Helios 2 satellite held the record for the closest approach to the Sun at 27 million kilometers, and scientists thought it might give them an idea of what they could expect. "When a mission like Parker is going to see things that no one has ever seen before, a mere glimpse of what could be observed is really helpful," Di Matteo said.
The problem with studying the solar wind of the Earth is the distance. At a time when solar wind is needed to travel the 150 million kilometers that separate us from the Sun, important clues to the origins of the wind – such as temperature and density – fade away. "You are constantly wondering," What I see here is due to the evolution of our four days of transit, and how much has come directly from the Sun? Solar energy scientist Nicholeen Viall, who advised Di Matteo during his research at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said Helios data – some of which was collected at one-third of the distance between the Sun and the Earth – could help them begin to answer these questions.
Blobs modeling
The first step was to trace Helios' measurements of blobs to their source on the sun. "You can view data from a spaceship anything you want, but if you can relate them to their origin in the Sun, it tells a more complete story," said Samantha Wallace, one of the collaborators of the study and a doctor in physics. . student at the University of New Mexico at Albuquerque.
Wallace used an advanced solar wind model to connect magnetic maps of the solar surface to Helios observations, a delicate task since computer languages and data conventions have changed considerably since the time of World War II. ; Helios. Now, researchers could see what kind of regions of the sun could ignite under the drops of solar wind.
Sift the evidence
Then, Di Matteo searched the data for specific wave patterns. They expected the conditions to alternate – warm and dense, then cold and faint – as individual blobs invaded the spacecraft and moved in a long line.
The perfect grounds found by Di Matteo have worried him. "It was a red flag," said Viall. "The current solar wind does not have such accurate and clean periodicities.Usually, when you get such a precise frequency, an instrument effect occurs." They may not have taken into account certain elements of instrument design, that is, they conveyed effects that were to be separated from true solar wind models.
Di Matteo needed more information about Helios instruments. But most of the researchers who worked at the mission have been retiring for a long time. He did what someone else would do and turned to the internet.
After much research on Google and a weekend of online translators, Di Matteo has discovered a German instruction manual describing the instruments dedicated to the solar wind mission experience. Decades ago, when Helios was simply a project and no one had ever launched a spaceship in the sun, scientists did not know how to best measure the solar wind. Di Matteo learned that to prepare for different scenarios, they have equipped the probes with two different instruments that each measure certain properties of the solar wind in their own way. This is the culprit responsible for Di Matteo's perfect waves: the spaceship itself, alternating between two instruments.
After removing the data segments collected during the routine instrument change, the researchers searched the blobs again. This time, they found them. The team describes five cases where Helios caught blob trains. Scientists have already spotted these spots on Earth, but this is the first time they have studied them as close to the Sun and with this level of detail. They point to the first conclusive evidence that blobs are warmer and denser than the typical solar wind.
The return of blobs
Blobs trains boil at intervals of 90 minutes continuously or in bursts, and how much they vary between them, remains a mystery. "This is one of those studies that has raised more questions than we have answered, but it's perfect for Parker Solar Probe," said Viall.
Parker Solar Probe aims to study the Sun closely, seeking answers to basic questions about the solar wind. "This is going to be very helpful," said Aleida Higginson, assistant project scientist at the Applied Physics Laboratory at Johns Hopkins University, Laurel, Maryland. "If you even want to start understanding things you've never seen before, you need to know what we've measured before and have a solid scientific interpretation."
Parker's solar probe makes its second solar flyby on April 4, bringing it closer to 15 million kilometers from the Sun, halving Helios 2's record distance. Researchers are eager to see if spots appear in Parker's observations. Eventually, the spaceship will become so close that it could catch blobs just after their formation, at the exit of the sun.
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