Of particular use was an instrument aboard STEREO-A called a coronagraph, which blocks overpowering light from the Sun to better image the faint outer atmosphere or corona. STEREO-A’s vantage point by Earth allows it to see regions of the corona as the Parker Solar Probe flies through them, resulting in a novel combination of measurements and an unparalleled view of solar wind structures and magnetic disturbances flowing out from the Sun.

STEREO images of the solar wind that Parker Solar Probe sampled, but using running difference (i.e. image processing to enhance the smaller features). Credit: NASA/STEREO/Angelos Vourlidas.

A surprisingly active system

The Parker Solar Probe has also been able to shed new light on invisible processes that occur within the solar wind, revealing that there is a surprisingly active system in proximity to our star.

“We think of the solar wind — as we see it near Earth — as very smooth, but Parker saw a surprisingly slow wind, full of little bursts and jets of plasma,” Tim Horbury, a lead researcher on Parker Solar Probe’s FIELDS instruments based at Imperial College London, says.

Horbury used data from Parker Solar Probe’s FIELDS instruments — which measure the scale and shape of electric and magnetic fields near the spacecraft — to examine in detail one particularly odd event, magnetic switchbacks — the solar magnetic field suddenly bending back on itself. These switchbacks were first spotted in Parker Solar Probe’s initial results revealed last week.

The Sun, in UV light, during Parker Solar Probe’s first closest approach in its first orbit. White magnetic field lines are shown originating in a small coronal hole; kinks, based on real Parker measurements, show the switchbacks observed during the encounter. (Credit: Imperial College/Ronan Laker/GONG/NASA/HelioPy/PFSSPy)

The exact origin of switchbacks is a mystery, but there is a possibility that they may be signatures of the process that heats the corona to millions of degrees — hundreds of times hotter than the visible surface below. The fact that the corona is substantially hotter than the Sun’s surface is referred to by scientists as the ‘coronal heating mystery’ and has long been a bone of contention as it is so counter-intuitive to expectations. Researchers suspect that this conundrum is closely related to questions about how the solar wind is energized and accelerated.

Parker Solar Probe flew through several ‘switchbacks’ — tubes of fast solar wind emerging from coronal holes in the Sun’s upper atmosphere. Credit: NASA/GSFC/CIL/Adriana Manrique Gutierrez

“We think the switchbacks are probably related to individual energetic energy releases on the Sun — what we call jets,” says Horbury. “If these are jets, there must a very large population of small events happening on the Sun, so they would contribute a large fraction of the total energy of the solar wind.”

The Eye of the Storm

The solar wind is not the only source of material outflow from the Sun. Our star also spits out clouds of material known as coronal mass ejections (CMEs). CMEs are denser and often travel faster than the solar wind meaning they can also have an effect on space weather as well as causing issues for satellites and space technology.

the particle flow around the Earth as the CME strikes the magnetosphere. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

CMEs are also notoriously difficult to predict and many are not visible for instruments based on either Earth or the STEREO-A. Because of this, it’s not always possible to predict which CMEs will disturb Earth’s magnetic field and trigger space weather effects.

As the magnetic structure of the CME plays a crucial role in the effect it will have on space weather understanding this is quite important. This seems to be determined by the region of the Sun that emitted the CME. Spotting this region of emission is made even more difficult by the fact that some of these eruptions don’t leave clear signatures in images in the Sun’s disc. Fortunately, the Solar Parker Probe was actually hit by one of these ‘stealth CMEs’ during its first solar fly-by back in November 2018.

“Flying close to the Sun, Parker Solar Probe has a unique chance to see young CMEs that haven’t been processed from travelling tens of millions of miles,” says Kelly Korreck, head of science operations for Parker’s SWEAP instruments, based at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. “This was the first time we were able to stick our instruments inside one of these coronal mass ejections that close to the Sun.”

A coronal mass ejection or CME in action

In particular, Korreck used data from Parker’s FIELDS and SWEAP instruments to get a snapshot of the internal structure of the CME. SWEAP, the mission’s solar wind instruments, measures characteristics like velocity, temperature, and electron and proton densities of the solar wind. These measurements not only provide one of the first looks inside a CME so close to the Sun, but they may help scientists learn to trace stealth CMEs back to their sources.

A violent CME erupts from the Sun. These events are denser and often travel faster than solar winds (NASA)

Another type of solar storm consists of extremely energetic particles moving near the speed of light. Though often related to CME outbursts, these particles are subject to their own acceleration processes — and they move much faster than CMEs, reaching Earth and spacecraft in a matter of minutes. These particles can damage satellite electronics and endanger astronauts, but their speed makes them more difficult to avoid than many other types of space weather.

These bursts of particles often accompany other solar events like flares and CMEs, but predicting when they will occur is difficult. Before particles reach near-light speed making them hazardous to spacecraft, electronics and astronauts, they experience a multi-stage energization process. The first step in this process which occurs near the Sun had yet to be directly observed.

Whilst travelling away from the Sun after its second solar fly-by the spacecraft observed the largest-yet energetic particle-event seen by the mission. Measurements taken by the energetic particle instrument suite during this encounter have filled in the missing link in the processes of particle energization.

“The regions in front of coronal mass ejections build-up material, like snowploughs in space, and it turns out these ‘snowploughs’ also build up material from previously released solar flares,” explains Nathan Schwadron, a space scientist at the University of New Hampshire in Durham.

Understanding how solar flares create populations of seed particles that feed energetic particle-events assist in more accurate predictions of when such events might happen. Additionally, this improved understanding should enable scientists to create more accurate models of how these events travel through space.

Fingerprinting asteroids

The Parker Solar Probe has been able to identify the cause of the spectacular Geminids meteor shower which light up the night sky over Earth. (Getty Images)

Parker Solar Probe’s WISPR instruments — designed to capture detailed images of the faint corona and solar wind — were able to spot another difficult-to-see cosmic structure, namely a 60,000-mile-wide dust trail following the orbit of the asteroid Phaethon, which creates the Geminids meteor shower.

Our planet’s and Phaethon’s orbits intersect each December, our atmosphere is showered with dust grains from this trail. These dust grains burn up and produce the spectacular show we call the Geminids. Scientists have long known that Phaethon spawns the Geminids, but seeing the actual dust trail hasn’t been possible until now.

Composite of the PSP/WISPR Inner and Outer cameras during the first solar encounter (Nov 2018). The location and relative size of the Sun are shown to scale, remaining just outside of the field of view and allowing WISPR to observe solar outflow and coronal mass ejections. Many stars and the Milky Way can be seen crossing the images. Credit: Brendan Gallagher/Karl Battams/NRL

As a result of it being both extremely faint and very close to the Sun in the sky, the trail had never been picked up by any previous telescope, despite numerous attempts. But, as WISPR is designed to see faint structures near the Sun it was capable of grabbing a direct view of the dust trail, thus granting researchers with a wealth of new information about its characteristics.

This image, taken from highlights the location of the very faint dust trail we observe following Phaethon’s orbit. Credit: Brendan Gallagher/Karl Battams/NRL

“We calculate a mass on the order of a billion tons for the entire trail, which is not as much as we’d expect for the Geminids, but much more than Phaethon produces near the Sun,” says Karl Battams, a space scientist at the U.S. Naval Research Lab in Washington, D.C. “This implies that WISPR is only seeing a portion of the Geminid stream — not the entire thing — but it’s a portion that no one had ever seen or even knew was there, so that’s very exciting!”

The release of this data and the additional findings mark the end of the Parker Solar Probe’s third fly-by of the Sun. The next orbit change will occur during the Venus flyby on Boxing Day and will bring the probe to within 11.6 million miles of the Sun’s surface — its next close approach in late January.

Thus craft’s mission will continue over the course of 21 progressively-closer solar flybys leading to an unparalleled investigation of our home star.