Parker Solar Probe reveals magnetic twists

17 December 2019

Interview with 

Christopher Chen, Queen Mary University London

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Adam Murphy has been speaking with Christopher Chen about new papers published in Nature, which shed some light what the Parker Solar Probe has been up to...

Adam - in August of 2018, NASA launched the Parker Solar Probe, and sent it hurtling off towards the Sun to further our understanding of the source of our sunlight. The probe is about the size of a car, with a heat shield covering one side so that it can withstand the enormously high temperatures. The other side has a suite of instruments on it, like magnetic field detectors to help us probe into the Sun. The probe is currently orbiting the Sun, getting closer and closer to its atmosphere, which is known as the corona. Now as it approaches, it's discovered something unusual in the Sun's magnetic field, which may help to explain some of the deepest mysteries about the Sun, like how the atmosphere surrounding it is hundreds of times hotter than the surface. I heard how from Christopher Chen at Queen Mary University London, who was involved with interpreting the data from one of the solar probe’s instruments.

Christopher - We found several new and unexpected discoveries. So one of these is the fact that we found these big folds in the magnetic field near the Sun. So the spacecraft has a magnetic field sensor, and what it found was that within the period of a few seconds, the magnetic field flips direction entirely. So at one moment it's pointing away from the Sun and then in a few seconds later, it flips to be pointing towards the Sun, and then it flips again and is pointing away from the Sun again. And this is sort of unexpected. It's not been seen further out and we don't know exactly what is causing these large flips in the magnetic field.

Adam - And that kind of thing doesn't happen here on Earth, does it?

Christopher - In the solar wind at earth, there are large amplitude fluctuations in the magnetic field, but these flips are certainly not as clear and pronounced as we're seeing up close to the Sun. It looks like a different type of structure that's occurring. Yeah.

Adam - And as it's getting closer, is it changing those flips, or how static are they?

Christopher - So they are getting more intermittent and more bursty. What is seen is that, as we're going closer to the Sun,  there are these periods where the solar wind is very, very quiet and the magnetic field is not flipping at all. But then there are these periods where it's flipping all over the place, and really rapidly, and at all kinds of timescales as well. So some of these, so we call them switch backs, so some of these switchbacks last for just a couple of seconds. Some of them last for minutes. So it's really much more bursty and much more, sort of, complex and dynamic up close to the Sun.

Adam - Given how big the Sun is, given the scale of it, the idea that the magnetic field can flip over the course of seconds seems really, really intense to me.

Christopher - Yeah, so when I say the magnetic field's flipping, it's not the entire magnetic field of the Sun, but it's the magnetic field in the solar wind where the spacecraft is measuring. So if you think of the magnetic field around the Sun, it's not as simple shape that you'd get from a bar magnet, but it's actually a really complex, intricate structure. So there's loops of magnetic field on the Sun. There are these long striations of magnetic field lines that that stretch far out into solar wind. So it's really the flips within this structure of the magnetic field as it points away from the Sun.

Adam - And what other kinds of things is the Solar Probe measuring?

Christopher - So for example, there's an instrument which measures the solar wind velocity as it travels away from the Sun. And what that found was that as we're going in closer, the solar wind is not flowing just radially away from the Sun in straight line, the solar wind is spinning around in a circle as it's traveling away from the Sun. But this speed of the spin is much faster than we expected from our models. So we say that things that are spinning have angular momentum, and the solar wind is something which can transport angular momentum away from the Sun. So what that's really causing is the Sun to be spinning at a slower rate than it otherwise would be. So the solar wind is carrying away the spin from the Sun.

Adam - And what implications do these results have for our understanding of the Sun?

Christopher - So they're really sort of changing our view of what's happening. One of the big mysteries of the Sun, and solar physics is something known as the coronal heating problem. So the corona is at a temperature of more than a million degrees, whereas the surface of the Sun is at a few thousand degrees. So it's really the atmosphere of the Sun is hundreds of times hotter than its surface. And this has been a long standing mystery in solar physics. So one of the things we're finding is that the amplitude of the fluctuations are getting much larger as we're going in closer. So as I said, we have these big folds in the magnetic field, and they contain a lot of energy in them. So we're thinking that these are involved somehow in the process which is causing the corona to be heated to such high temperatures. And another thing is the existence of the solar wind itself, the solar wind, by the time it gets to the Earth is traveling at around a million miles per hour or so. And it's again another open question as to how the solar wind comes to be traveling so fast. We think again that these large amplitude fluctuations, and this sort of complex, chaotic dynamic environment is providing the energy to push the solar wind and cause it to be accelerated to these large speeds.

Adam - Lastly, what's next for the solar probe? What's it going to start measuring now?

Christopher - So over the next few years, it's going to be getting gradually closer and closer to the Sun. And one thing that we expect to happen, within perhaps the next year or two, is it to cross within the solar corona itself. So it has not got within the corona yet, but we're expecting it to do so within the next few years. And then it's really going to be in a completely new, unexplored area of space. Right up close to the Sun.

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