Signs of Success: At Mission’s Midpoint, Parker Solar Probe Marks Amazing Achievements

May 24, 2022

Signs of Success

At Mission's Midpoint, Parker Solar Probe Marks Amazing Achievements

By Michael Buckley

In August 2018, NASA's Parker Solar Probe embarked on an unprecedented voyage to study the Sun and its environment closer than any spacecraft before it. As the probe aimed for 24 progressively closer passes around the Sun, tops on the mission's to-do list were three key scientific goals:

• Trace the flow of energy that heats the Sun's outer atmosphere
• Shed light on the sources of the solar wind, the constant flow of energetic material escaping from the Sun
• Explore how solar energetic particles - some of which can make the 93-million-mile (150-million-kilometer) journey to Earth in a matter of minutes - are transported and accelerated

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Nearly four years after launch, the mission, managed for NASA by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, has made significant inroads toward achieving these goals - enough so that NASA already considers the mission a success. But with its 12th closest approach set for June 1, Parker Solar Probe continues to break records and capture first-of-its-kind measurements of the Sun.

"Parker Solar Probe set out to revolutionize our knowledge of the Sun, in a way that no other mission had ever attempted," said Nour Raouafi, Parker Solar Probe project scientist from APL. "We have already made breakthrough discoveries in a region of the solar system that has never been explored by a spacecraft, and the best still might be yet to come."

Here are some need-to-know facts about NASA's historic mission to touch the Sun.

1. Parker Solar Probe was the first NASA mission named for a living person.

In honor of Eugene N. Parker, eminent physicist who first predicted the solar wind, NASA announced in May 2017 that it would rename the Solar Probe Plus mission to Parker Solar Probe. Parker witnessed the spacecraft's launch in person and delighted in the discoveries made in the mission's few years. He died on March 15, 2022, at age 94, but as Raouafi said at the time, "Gene Parker has been a transformative figure in heliophysics and space research and will continue to live with us through his pioneering research."

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2. The APL-built spacecraft carries revolutionary technology.

The "solar probe" mission was conceived in 1958, but it took 60 years to develop the technology to make it happen. Designed, built and now operated at APL, Parker Solar Probe is fortified to survive the scorching environs near a star - this includes a heat shield (known as the thermal protection system), autonomous onboard "smarts" to keep that shield facing the Sun, and a novel, efficient cooling system that uses circulating water.

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"Parker Solar Probe has exceeded expectations, performing much better in space and resulting in even greater science return than we anticipated," said Susan Ensor, the mission's deputy project manager from APL. "Less power degradation, better downlink rates and temperatures below our prelaunch models all contributed to more flexible operations and made possible greatly enhanced returns. Our plan before launch was to gather science data only when the spacecraft was within 0.25 astronomical units - about 23 million miles - of the Sun's center. But since launch, we have been able to keep instruments on for more than 75% of Parker's orbit around the Sun, about eight times longer than expected."

For the probe's first few close encounters with the Sun, the mission operations team anxiously awaited the arrival of "green" beacon tones, or radio signals, indicating a healthy spacecraft and nominal solar encounter operations.

"Parker Solar Probe performed extremely well during its first close approaches to the Sun, and remains very healthy under increasingly strenuous conditions," said Nickalaus Pinkine, the mission operations manager from APL. Based on the success of earlier orbits, the team is very comfortable extending the science operations to larger sections of each orbit and returning much more data to Earth."

3. Parker Solar Probe is a repeat record-breaker.

Just a few months after launch, Parker Solar Probe became the closest human-made object to the Sun, passing within 26.55 million miles (42.72 million kilometers) of the Sun's surface, and became the fastest human-made object, reaching speeds of 153,454 miles per hour. Since then, it has repeatedly broken both of those records, and will reach a top speed of about 430,000 miles per hour (700,000 kilometers per hour) as it flies to within 3.9 million miles (6.2 million kilometers) of the Sun's surface in 2024.

Follow Parker Solar Probe around the Sun in real time here.

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4. Parker Solar Probe has officially sampled the Sun.

In December 2021, NASA announced that Parker Solar Probe had achieved its cornerstone objective: making the first measurements from within the atmosphere of a star, effectively becoming the first spacecraft to "touch the Sun."

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5. It has made game-changing discoveries.

Parker Solar Probe carries four instrument suites, and each is credited with several groundbreaking discoveries. Here's a quick look at some of them:

The Solar Wind Electrons Alphas and Protons investigation (SWEAP)

Sampling the Solar Atmosphere

When Parker Solar Probe entered the solar atmosphere on April 28, 2021, it made the first-ever crossing of what's known as the Alfvén critical surface - the boundary where solar material anchored to the Sun first escapes and becomes the solar wind.

Until this crossing, no one knew what that boundary would look like. During its first pass close enough to cross the boundary, Parker Solar Probe passed into and out of the corona several times. This revealed key information about the boundary's shape; rather than resembling a smooth ball, the Alfvén critical surface is wrinkled with spikes and valleys.

"Sampling the solar wind below the Alfvén critical boundary is essential to understanding the heating and acceleration of the solar wind," said Justin Kasper, the SWEAP principal investigator from BWX Technologies. "If these early results are any indication, some incredible discoveries await us as Parker Solar Probe flies deeper into the solar atmosphere."

SWEAP established that the wrinkles stemmed from coronal streamers - giant plumes of solar material rising through the Sun's atmosphere. Streamers have long been observed by Sun-watching spacecraft near Earth, but never before measured directly.

"The results are reshaping what we know about the Sun's atmosphere and how it transforms into the solar wind," Raouafi said.

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The Wide-Field Imager for Parker Solar Probe (WISPR)

Discovering the Dust-Depletion Zone

Dust is just about everywhere in our solar system - the remnants of collisions that formed planets, asteroids, comets and other celestial bodies billions of years ago. Almost a century ago, astronomer Henry Norris Russell predicted a region around the Sun where dust particles should get hot enough to sublimate and thus disappear, creating a dust-free zone. People looked for evidence of the sublimation zone for decades, but there was no consistent evidence for its existence.

The WISPR instrument made the first detection of dust depleting close to the Sun, observing the light reflected from dust dimming at about 19 solar radii (8.2 million miles, or 13.2 million kilometers, from the Sun). Models of the results suggest that a dust-free zone should exist starting at about 5 solar radii (2.2 million miles, or 3.5 million kilometers, from the Sun).

"Discovering the dust-depletion zone around the Sun is not only historical, but also insightful on the environment near of the Sun and other stars," said Mark Linton, WISPR principal investigator from the Naval Research Laboratory.

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FIELDS

Tracking Down the Sun's Magnetic Reversals

When Parker Solar Probe sent back the first observations from its trek toward the Sun, scientists found their magnetic field measurements spiked with what became known as switchbacks: rapid flips in the Sun's magnetic field that reversed direction like a zig-zagging mountain road.

FIELDS has since helped narrow down their origins. During Parker Solar Probe's sixth flyby of the Sun, FIELDS data revealed that the switchbacks aligned with magnetic "funnels" in the solar surface. These funnels emerge from between structures called supergranules - giant bubbles on the Sun in which hot plasma from the solar interior rises up, spreads out across the surface, cools and then sinks back down. The magnetic geometry of these regions suggests that magnetic reconnection powers the solar wind.

"The recent data from Parker Solar Probe link the solar wind to its sources at the base of the corona," said Stuart Bale, the FIELDS principal investigator from the University of California, Berkeley. "This is essential to understanding the heating and the acceleration of the plasma flow that permeates the whole solar system."

But while the findings locate where switchbacks are made, researchers are still digging into the question of how they're formed.

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The Integrated Science Investigation of the Sun (ISʘIS)

Rewriting the Book on Solar Energetic Particles

ISʘIS (pronounced "ee-sis" and including the symbol for the Sun in its acronym) measures solar energetic particles (SEPs), the most energetic particles that escape the Sun. Measured near Earth, SEP events are relatively rare and hard to predict. But detecting SEPs close to the Sun, ISʘIS has changed just about everything we know about these speedy particles. ISʘIS has found that SEPs are much more common than expected, that they contain a wider range of types of particles than expected and that their paths from the Sun are not as direct as previously thought - they can be disrupted by the switchbacks detected by FIELDS and can at times follow a path twice as long as expected.

By measuring these events so close to the Sun, ISʘIS is detecting events so small that all trace of them is lost before they reach Earth, helping scientists develop a fuller picture of where they come from and how they're accelerated away from the Sun.

"Even though Parker Solar Probe launched during the relative "quiet" of a deep solar minimum, we made many new and exciting discoveries important to understanding the sources, acceleration and transport of these high-energy particles near the Sun and out in the heliosphere," said David McComas, the ISʘIS principal investigator from Princeton University.

As the Sun becomes more active - approaching solar maximum - scientists eagerly await Parker Solar Probe's flights through large eruptive events close to the Sun, and what they reveal about how hazardous energetic particles are accelerated and transported through the heliosphere.

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…And the results keep coming.

Each new data set expands the limits of space science - and it's not just about the Sun. Parker Solar Probe has also studied comets, detected radio emissions from Venus' atmosphere and even captured the first-ever images of Venus' surface in visible wavelengths.

With its closest passes of the Sun still ahead in 2024 and 2025, only time will tell what new discoveries await.

"The Parker Solar Probe mission is not only reshaping the landscape of solar and heliophysics research before our eyes, but it is enticing us to pursue challenging ideas that, just a few years ago, we considered out of reach," said Raouafi. "I can't say enough about the exemplary team of scientists, engineers and managers at NASA, APL and our partner institutions who have made this mission a success. We're excited about the future of Parker Solar Probe and the opportunity to inspire missions that will follow its path."

Media contact: Michael Buckley, 240-228-7536, [email protected]

The Applied Physics Laboratory, a not-for-profit division of The Johns Hopkins University, meets critical national challenges through the innovative application of science and technology. For more information, visit www.jhuapl.edu.