Dec 5 2019
The latest evidence of the origins of the solar wind has been revealed by the Parker Solar Probe spacecraft, which has traveled closer to the Sun than any mission carried out so far.
“Switchbacks” of faster solar wind emerge from coronal holes near the Sun’s equator. Image Credit: Ronan Laker/GONG/NASA/HelioPy/PFSSPy.
August 2018 saw the launch of the Parker Solar Probe developed by NASA. The initial results of the probe were recently published in a series of four papers in the Nature journal. Researchers, including those from Imperial College London, were trying to figure out certain crucial data to demonstrate how the solar wind rapidly moves away from the Sun’s surface.
The solar wind is essentially a stream of charged particles produced by the Sun filling the Solar System. While the solar wind is responsible for the Southern and Northern lights, it can also lead to disruption at the time of intense episodes like coronal mass ejections and solar flares, displacing satellites and power grids.
An international group of researchers has now demonstrated that bursty “spikes” of solar wind occur in holes in the Sun’s external atmosphere close to its equator. Magnetic phenomena accelerate these spikes as they flow past the Earth and into the deep space.
According to the latest study, the spikes are produced by a process called “magnetic reconnection” close to the Sun. This process pulls on the stressed lines of the Sun’s magnetic field, producing “switchbacks” or folds. Events like these persist only for a few minutes but discharge an enormous amount of energy, rapidly moving the solar wind away in long tubes measuring approximately equivalent to the Earth’s diameter.
Fast, Energetic Wind
The discovery is based on the data obtained from the HELIOS missions. These missions were launched in the 1970s and were the former record-holders for approaching closest to the Sun.
Professor Tim Horbury from the Department of Physics at Imperial College London is a co-investigator on the FIELDS instrument of the Parker Solar Probe. The University of California, Berkeley headed the FIELDS instrument project.
From HELIOS data we could see what might be ‘spikes’ of faster solar wind, and now we have been able to confirm their existence in striking detail with Parker Solar Probe.
Tim Horbury, Professor, Department of Physics, Imperial College London
Horbury continued, “We usually think of the fast solar wind as very smooth, but Parker Solar Probe saw surprisingly slow wind with a large number of these little bursts and jets of plasma, creating long tubes of fast wind containing plasma with around twice the energy of the background solar wind.”
Closest Approach
The Sun’s outer atmosphere, known as the corona, is being investigated by the Parker Solar Probe. To achieve this, the solar probe is being passed through the corona to gain a deeper understanding of the solar wind's origins.
For the latest research, the Parker Solar Probe collected data from a distance of 24 million kilometers from the Sun, within the Mercury orbit. In the future, the Parker Solar Probe will travel successively nearer to the Sun and ultimately reach a distance of below six million kilometers from the Sun’s surface and much closer than the average distance of 150 million kilometers of Earth.
Researchers are aware that the solar wind’s properties vary as it travels from the Sun and moves toward the Earth; hence, investigating the solar wind nearer its origin should reveal more about the way it is produced and how it evolves.
Pairing with Solar Orbiter
Next year, the Parker Solar Probe will be joined by a European Space Agency mission, called Solar Orbiter, with the Imperial kit onboard.
Although Parker Solar Probe will get even more accurate measurements of the young solar wind at its closest approach, it’s too close for telescopes, so it won’t be able to see what features on the surface of the Sun may be creating the structures of the solar wind.
Tim Horbury, Professor, Department of Physics, Imperial College London
Horbury continued, “This is where Solar Orbiter comes in. It will not go as close to the Sun, but will have sophisticated telescopes and instruments on board that will be able to see from a distance what might be causing phenomena Parker Solar probe is detecting up close, forming a fuller picture of what creates and accelerates the solar wind.”
The initial data provided other results that include the measurement of the solar wind speed. Instead of flowing radially away from the Sun, the solar wind flows sideways at a speed of 15 to 25 times faster than estimated; a “snowplow” effect also occurs wherein charged particles bunch up before a coronal mass ejection event accelerates them away from the Sun.
Undergraduate Contributions
At the Department of Physics, two undergraduate students were involved in investigating the data from the Parker Solar Probe and are presently pursuing their work as PhD students. Both undergraduates have been named as authors on one of the papers.
Ronan Laker assisted in mapping the type of magnetic field lines from the Sun detected by the Parker Solar Probe and thus helped in formulating the concept that the solar wind observed was actually emerging from a tiny coronal hole.
It has been exciting to see how something we contributed to as part of our degree has made it into one of the most prestigious science journals. These first results are really exciting, as, whilst there is evidence of these spikes in the magnetic field, their origin and nature is still open for discussion. We hope to contribute to this future area of research through our respective PhDs at Imperial.
Ronan Laker, Undergraduate Student, Department of Physics, Imperial College London
Thomas Woolley studied the deflections, durations, periodicity, and occurrence rates of the spikes of the rapid solar wind, seeking answers, for instance, whether the occurrence of one spike meant that another one was probably going to follow immediately.
He stated, “We are both very happy to have been given the opportunity to work on Parker Solar Probe during our MSci project. At the start, we didn’t know where the project would lead, which can often be the case with new space missions. We are however pleased with how the project progressed and glad that we were able to contribute to the wider scientific community.”
Space switchbacks
Parker Solar Probe flew through several “switchbacks”—tubes of fast solar wind emerging from coronal holes in the Sun’s upper atmosphere. Video Credit: NASA.