- 3405 - PARKER SOLAR PROBE - reaching the Sun’s corona? While saying that the Parker Solar Probe “touched the Sun” might be a bit of hyperbole, the spacecraft has since come closer to the Sun as it spirals in an ever-tightening orbit. Parker’s latest closest passed just 5.3 million miles from the solar surface. Data from that pass will be sent to Earth starting on December 23, 2020.
--------- 3405 - PARKER SOLAR PROBE - reaching the Sun’s corona?
- The Parker Solar Probe passed through the out portion of the Sun’s corona in April of 2021, passing directly through streamers of solar plasma. Data from the spacecraft’s WISPR (Wide-field Imager for Parker Solar PRobe) instrument while breaching the corona came from Parker’s close pass on April 28, 2021, during its eighth flyby of the Sun, traveling at an incredible 142 kilometers per second.
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- While it was 18.8 solar radii (8.127 million miles) above the solar surface itself, the spacecraft flew through the part of the corona that is visible during a solar eclipse.
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- The Sun’s corona is made of superheated gases that are bound to the Sun by gravity and magnetic forces. As that material gets pushed away from the Sun by rising heat and pressure, it reaches a point where the gravitational forces and magnetic fields are too weak to contain it.
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- That point is known as the “Alfvén critical surface“, and until now, researchers were unsure exactly where that point was. But from data sent back by Parker, researchers knew from the specific magnetic and particle conditions that the spacecraft had breached that point, finally entering the solar atmosphere.
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- Researchers are still working on understanding the data, and have unraveled clues about some bizarre S-shaped kinks in the solar wind’s magnetic field lines, called switchbacks, which appear to put charged particles on a zig-zag path as they escaped the Sun.
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- They are also hoping to resolve a longstanding solar mystery about how the corona is heated to millions of degrees, hotter than the Sun surface itself.
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- During the next four years, Parker will eventually reach as close as 8.86 solar radii (3.83 million miles) from the surface.
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- The new milestone marks one major step for Parker Solar Probe and one giant leap for solar science. Touching the very stuff the Sun is made of will help scientists uncover critical information about our closest star and its influence on the solar system.
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- As it circles closer to the solar surface, Parker is making new discoveries that other spacecraft were too far away to see, including from within the solar wind, the flow of particles from the Sun that can influence us at Earth.
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- In 2019, Parker discovered that magnetic zig-zag structures in the solar wind, called switchbacks, are plentiful close to the Sun. But how and where they form remained a mystery. Halving the distance to the Sun since then, Parker Solar Probe has now passed close enough to identify one place where they originate: the solar surface.
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- Unlike Earth, the Sun doesn't have a solid surface. But it does have a superheated atmosphere, made of solar material bound to the Sun by gravity and magnetic forces. As rising heat and pressure push that material away from the Sun, it reaches a point where gravity and magnetic fields are too weak to contain it.
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- That point, the Alfvén critical surface, marks the end of the solar atmosphere and beginning of the solar wind. Solar material with the energy to make it across that boundary becomes the solar wind, which drags the magnetic field of the Sun with it as it races across the solar system, to Earth and beyond.
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- Beyond the Alfvén critical surface, the solar wind moves so fast that waves within the wind cannot ever travel fast enough to make it back to the Sun - severing their connection.
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- Based on remote images of the corona, estimates had put it somewhere between 10 to 20 solar radii from the surface of the Sun, 4.3 to 8.6 million miles. Parker's spiral trajectory brings it slowly closer to the Sun and during the last few passes, the spacecraft was consistently below 20 solar radii (91 percent of Earth's distance from the Sun), putting it in the position to cross the boundary..
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- On April 28, 2021, during its eighth flyby of the Sun, Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii (around 8.1 million miles) above the solar surface that told scientists it had crossed the Alfvén critical surface for the first time and finally entered the solar atmosphere.
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- Parker Solar Probe passed into and out of the corona several times. This is proved what some had predicted, that the Alfvén critical surface isn't shaped like a smooth ball. Rather, it has spikes and valleys that wrinkle the surface. Discovering where these protrusions line up with solar activity coming from the surface can help scientists learn how events on the Sun affect the atmosphere and solar wind.
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- At one point, as Parker Solar Probe dipped to just beneath 15 solar radii (around 6.5 million miles) from the Sun's surface, it transited a feature in the corona called a pseudostreamer. “Pseudostreamers” are massive structures that rise above the Sun's surface and can be seen from Earth during solar eclipses.
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- Passing through the pseudostreamer was like flying into the eye of a storm. Inside the pseudostreamer, the conditions quieted, particles slowed, and number of switchbacks dropped, a dramatic change from the busy barrage of particles the spacecraft usually encounters in the solar wind.
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- For the first time, the spacecraft found itself in a region where the magnetic fields were strong enough to dominate the movement of particles there. These conditions were the definitive proof the spacecraft had passed the Alfvén critical surface and entered the solar atmosphere where magnetic fields shape the movement of everything in the region.
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- Parker will continue to spiral closer to the Sun, eventually reaching as close as 8.86 solar radii (3.83 million miles) from the surface. Upcoming flybys, the next of which is happening in January, 2022, will likely bring Parker Solar Probe through the corona again.
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- The size of the corona is also driven by solar activity. As the Sun's 11-year activity cycle - the solar cycle - ramps up, the outer edge of the corona will expand, giving Parker Solar Probe a greater chance of being inside the corona for longer periods of time.
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- On recent solar encounters, Parker Solar Probe collected data pinpointing the origin of zig-zag-shaped structures in the solar wind, called switchbacks. The data showed one spot that switchbacks originate is at the visible surface of the Sun - the photosphere.
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- By the time it reaches Earth, 93 million miles away, the solar wind is an unrelenting headwind of particles and magnetic fields. But as it escapes the Sun, the solar wind is structured and patchy.
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- In the mid-1990s, the NASA-European Space Agency mission Ulysses flew over the Sun's poles and discovered a handful of bizarre S-shaped kinks in the solar wind's magnetic field lines, which detoured charged particles on a zig-zag path as they escaped the Sun. For decades, scientists thought these occasional switchbacks were oddities confined to the Sun's polar regions.
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- In 2019, at 34 solar radii from the Sun, Parker discovered that switchbacks were not rare, but common in the solar wind. This renewed interest in the features and raised new questions: Where were they coming from? Were they forged at the surface of the Sun, or shaped by some process kinking magnetic fields in the solar atmosphere?
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- The clues came as Parker orbited closer to the Sun on its sixth flyby, less than 25 solar radii out. Data showed switchbacks occur in patches and have a higher percentage of helium - known to come from the photosphere - than other elements.
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- The switchbacks' origins were further narrowed when the scientists found the patches aligned with magnetic funnels that emerge from the photosphere between convection cell structures called supergranules.
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- In addition to being the birthplace of switchbacks, the scientists think the magnetic funnels might be where one component of the solar wind originates. The solar wind comes in two different varieties - fast and slow - and the funnels could be where some particles in the fast solar wind come from.
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- The structure of the regions with switchbacks matches up with a small magnetic funnel structure at the base of the corona. Understanding where and how the components of the fast solar wind emerge, and if they're linked to switchbacks, could help scientists answer a longstanding solar mystery: how the corona is heated to millions of degrees, far hotter than the solar surface below.
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- While the new findings locate where switchbacks are made, the scientists can't yet confirm how they're formed. One theory suggests they might be created by waves of plasma that roll through the region like ocean surf. Another contends they're made by an explosive process known as magnetic reconnection, which is thought to occur at the boundaries where the magnetic funnels come together.
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January 11, 2022 PARKER SOLAR PROBE - reaching the Sun’s corona? 3405
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