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Author Topic:   NASA Parker Solar Probe to skim the Sun
Robert Pearlman
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NASA release
NASA Selects Investigations for First Mission to Encounter the Sun

NASA has begun development of a mission to visit and study the sun closer than ever before. The unprecedented project, named Solar Probe Plus, is slated to launch no later than 2018.

The small car-sized spacecraft will plunge directly into the sun's atmosphere approximately four million miles from our star's surface. It will explore a region no other spacecraft ever has encountered. NASA has selected five science investigations that will unlock the sun's biggest mysteries.

"The experiments selected for Solar Probe Plus are specifically designed to solve two key questions of solar physics -- why is the sun's outer atmosphere so much hotter than the sun's visible surface and what propels the solar wind that affects Earth and our solar system? " said Dick Fisher, director of NASA's Heliophysics Division in Washington. "We've been struggling with these questions for decades and this mission should finally provide those answers."

As the spacecraft approaches the sun, its revolutionary carbon-composite heat shield must withstand temperatures exceeding 2550 degrees Fahrenheit and blasts of intense radiation. The spacecraft will have an up close and personal view of the sun enabling scientists to better understand, characterize and forecast the radiation environment for future space explorers.

NASA invited researchers in 2009 to submit science proposals. Thirteen were reviewed by a panel of NASA and outside scientists. The total dollar amount for the five selected investigations is approximately $180 million for preliminary analysis, design, development and tests.

The selected proposals are:

  • Solar Wind Electrons Alphas and Protons Investigation: principal investigator, Justin C. Kasper, Smithsonian Astrophysical Observatory in Cambridge, Mass.

    This investigation will specifically count the most abundant particles in the solar wind -- electrons, protons and helium ions -- and measure their properties. The investigation also is designed to catch some of the particles for direct analysis.

  • Wide-field Imager: principal investigator, Russell Howard, Naval Research Laboratory in Washington. This telescope will make 3-D images of the sun's corona, or atmosphere. The experiment will also provide 3-D images of the solar wind and shocks as they approach and pass the spacecraft. This investigation complements instruments on the spacecraft providing direct measurements by imaging the plasma the other instruments sample.

  • Fields Experiment: principal investigator, Stuart Bale, University of California Space Sciences Laboratory in Berkeley, Calif. This investigation will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the sun's atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna.

  • Integrated Science Investigation of the Sun: principal investigator, David McComas of the Southwest Research Institute in San Antonio.

    This investigation consists of two instruments that will monitor electrons, protons and ions that are accelerated to high energies in the sun's atmosphere.

  • Heliospheric Origins with Solar Probe Plus: principal investigator, Marco Velli of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Velli is the mission's observatory scientist, responsible for serving as a senior scientist on the science working group. He will provide an independent assessment of scientific performance and act as a community advocate for the mission.
"This project allows humanity's ingenuity to go where no spacecraft has ever gone before," said Lika Guhathakurta, Solar Probe Plus program scientist at NASA Headquarters, in Washington. "For the very first time, we'll be able to touch, taste and smell our sun."

The Solar Probe Plus mission is part of NASA's Living with a Star Program. The program is designed to understand aspects of the sun and Earth's space environment that affect life and society. The program is managed by NASA'S Goddard Space Flight Center in Greenbelt, Md., with oversight from NASA's Science Mission Directorate's Heliophysics Division. The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., is responsible for formulating, implementing and operating the Solar Probe Mission.

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The Johns Hopkins University Applied Physics Laboratory: Solar Probe Plus

Solar Probe Plus will swoop to within 4 million miles of the sun's surface, facing heat and radiation like no spacecraft before it. Launching in 2018, Solar Probe Plus will provide new data on solar activity and make critical contributions to our ability to forecast major space-weather events that impact life on Earth.

Solar Probe Plus is an extraordinary and historic mission exploring arguably the last and most important region of the solar system to be visited by a spacecraft to finally answer top-priority science goals for over five decades.

But we don't do this just for the basic science.

One recent study by the National Academy of Sciences estimated that without advance warning a huge solar event could cause two trillion dollars in damage in the US alone, and the eastern seaboard of the US could be without power for a year.

In order to unlock the mysteries of the corona, but also to protect a society that is increasingly dependent on technology from the threats of space weather, we will send Solar Probe Plus to touch the sun.

Robert Pearlman
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NASA release
NASA Renames Solar Probe Mission to Honor Pioneering Physicist Eugene Parker

NASA has renamed the Solar Probe Plus spacecraft — humanity's first mission to a star, which will launch in 2018 — as the Parker Solar Probe in honor of astrophysicist Eugene Parker. The announcement was made at a ceremony at the University of Chicago, where Parker serves as the S. Chandrasekhar Distinguished Service Professor Emeritus, Department of Astronomy and Astrophysics.

In 1958, Parker — then a young professor at the university's Enrico Fermi Institute — published an article in the Astrophysical Journal called "Dynamics of the interplanetary gas and magnetic fields." Parker believed there was high speed matter and magnetism constantly escaping the sun, and that it affected the planets and space throughout our solar system.

This phenomenon, now known as the solar wind, has been proven to exist repeatedly through direct observation. Parker's work forms the basis for much of our understanding about how stars interact with the worlds that orbit them.

"This is the first time NASA has named a spacecraft for a living individual," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate in Washington. "It's a testament to the importance of his body of work, founding a new field of science that also inspired my own research and many important science questions NASA continues to study and further understand every day. I'm very excited to be personally involved honoring a great man and his unprecedented legacy."

"The solar probe is going to a region of space that has never been explored before," said Parker. "It's very exciting that we'll finally get a look. One would like to have some more detailed measurements of what's going on in the solar wind. I'm sure that there will be some surprises. There always are."

In the 1950s, Parker proposed a number of concepts about how stars — including our sun — give off energy. He called this cascade of energy the solar wind, and he described an entire complex system of plasmas, magnetic fields and energetic particles that make up this phenomenon. Parker also theorized an explanation for the superheated solar atmosphere, the corona, which is — contrary to what was expected by physics laws — hotter than the surface of the sun itself. Many NASA missions have continued to focus on this complex space environment defined by our star — a field of research known as heliophysics.

"Parker Solar Probe is going to answer questions about solar physics that we've puzzled over for more than six decades," said Parker Solar Probe Project Scientist Nicola Fox, of the Johns Hopkins University Applied Physics Laboratory. "It's a spacecraft loaded with technological breakthroughs that will solve many of the largest mysteries about our star, including finding out why the sun's corona is so much hotter than its surface. And we're very proud to be able to carry Gene's name with us on this amazing voyage of discovery."

NASA missions are most often renamed after launch and certification; in this case, given Parker's accomplishments within the field, and how closely aligned this mission is with his research, the decision was made to honor him prior to launch, in order to draw attention to his important contributions to heliophysics and space science.

Born on June 10, 1927, in Michigan, Eugene Newman Parker received a Bachelor of Science in physics from Michigan State University and a doctorate from Caltech. He then taught at the University of Utah, and since 1955, Parker has held faculty positions at the University of Chicago and at its Fermi Institute. He has received numerous awards for his research, including the George Ellery Hale Prize, the National Medal of Science, the Bruce Medal, the Gold Medal of the Royal Astronomical Society, the Kyoto Prize, and the James Clerk Maxwell Prize.

Parker Solar Probe is on track for launch during a 20-day window that opens July 31, 2018. The mission is part of NASA's Living With a Star program to explore aspects of the sun-Earth system that directly affect life and society. LWS is managed by the agency's Goddard Space Flight Center in Greenbelt, Maryland, for NASA's Science Mission Directorate in Washington, D.C. Johns Hopkins APL manages the mission for NASA and is designing and building and will operate the spacecraft.

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NASA release
Parker Solar Probe Gets Its Revolutionary Heat Shield

On Sept. 25, 2017, media were invited to see NASA’s Parker Solar Probe in its flight configuration at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, where it is being built. The revolutionary heat shield that will protect the first spacecraft to fly directly into the Sun’s atmosphere was installed for the first time on Sept. 21. This is the only time the spacecraft will have its thermal protection system — which will reach temperatures of 2,500 degrees F while at the Sun — attached until just before launch.

Parker Solar Probe is scheduled for launch on July 31, 2018, from Cape Canaveral Air Force Station, Florida. The spacecraft will explore the Sun’s outer atmosphere and make critical observations that will answer decades-old questions about the physics of how stars work. The resulting data will improve forecasts of major space weather events that impact life on Earth, as well as satellites and astronauts in space.

Robert Pearlman
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NASA release
Parker Solar Probe Launch Window Extended

NASA's Parker Solar Probe, secured inside its payload fairing, was moved July 30, from nearby Astrotech Space Operations in Titusville, Florida, to Space Launch Complex 37 on Cape Canaveral Air Force Station. The following day, the spacecraft was lifted and attached to the top of the United Launch Alliance Delta IV Heavy rocket in the Vertical Integration Facility.

NASA and its mission partners have analyzed and approved an extended launch window for Parker Solar Probe until Aug. 23, 2018 (previously Aug. 19). The spacecraft is scheduled to launch no earlier than Aug. 11, 2018, at 3:33 a.m. EDT.

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NASA update
The launch team is targeting 3:53 a.m. EDT for liftoff of the United Launch Alliance Delta IV Heavy rocket carrying NASA’s Parker Solar Probe. The countdown is in progress at Cape Canaveral Air Force Station's Space Launch Complex 37.

Robert Pearlman
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United Launch Alliance release
The launch of a United Launch Alliance Delta IV Heavy carrying the Parker Solar Probe spacecraft was scrubbed today [Aug. 11] due to a violation of a launch limit, resulting in a hold. There was not enough time remaining in the window to recycle.

The launch is planned for Sunday, Aug. 12 from Space Launch Complex-37 at Cape Canaveral Air Force Station. The forecast shows a 60 percent chance of favorable weather conditions for launch. The launch time is 3:31 a.m. ET.

Robert Pearlman
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collectSPACE
NASA launches Parker Solar Probe on mission to 'touch the Sun'

NASA's first mission to "touch the Sun" produced an artificial sunrise as it left Earth.

The space agency's Parker Solar Probe, which will fly into the Sun's atmosphere, or corona — traveling closer to the Sun than any spacecraft in history — began its unprecedented journey in darkness on Sunday morning (Aug. 12) atop a United Launch Alliance (ULA) Delta IV Heavy rocket.

Riding the bright glowing plume of the booster's three rocket engines, the probe lifted off at 3:31 a.m. EDT (0731 GMT) from Launch Complex 37 at the Cape Canaveral Air Force Station. Less than an hour later, the spacecraft separated from the rocket's third stage to begin a three-month trip to the Sun — by way of a flyby of the planet Venus in September.

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NASA release
Parker Solar Probe Breaks Record, Becomes Closest Spacecraft to Sun

Parker Solar Probe now holds the record for closest approach to the Sun by a human-made object. The spacecraft passed the current record of 26.55 million miles from the Sun's surface on Oct. 29, 2018, at about 1:04 p.m. EDT, as calculated by the Parker Solar Probe team.

The previous record for closest solar approach was set by the German-American Helios 2 spacecraft in April 1976. As the Parker Solar Probe mission progresses, the spacecraft will repeatedly break its own records, with a final close approach of 3.83 million miles from the Sun's surface expected in 2024.

"It's been just 78 days since Parker Solar Probe launched, and we've now come closer to our star than any other spacecraft in history," said Project Manager Andy Driesman, from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "It's a proud moment for the team, though we remain focused on our first solar encounter, which begins on Oct. 31."

Parker Solar Probe is also expected to break the record for fastest spacecraft traveling relative to the Sun on Oct. 29 at about 10:54 p.m. EDT. The current record for heliocentric speed is 153,454 miles per hour, set by Helios 2 in April 1976.

The Parker Solar Probe team periodically measures the spacecraft's precise speed and position using NASA's Deep Space Network, or DSN. The DSN sends a signal to the spacecraft, which then retransmits it back to the DSN, allowing the team to determine the spacecraft's speed and position based on the timing and characteristics of the signal. Parker Solar Probe's speed and position were calculated using DSN measurements made on Oct. 24, and the team used that information along with known orbital forces to calculate the spacecraft's speed and position from that point on.

Parker Solar Probe will begin its first solar encounter on Oct. 31, continuing to fly closer and closer to the Sun's surface until it reaches its first perihelion — the point closest to the Sun — at about 10:28 p.m. EST on Nov. 5. The spacecraft will face brutal heat and radiation conditions while providing humanity with unprecedentedly close-up observations of a star and helping us understand phenomena that have puzzled scientists for decades. These observations will add key knowledge to NASA's efforts to understand the Sun, where changing conditions can propagate out into the solar system, affecting Earth and other worlds.

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NASA release
Parker Solar Probe Becomes Fastest-Ever Spacecraft

At about 10:54 p.m. EDT on Oct. 29, 2018, Parker Solar Probe surpassed 153,454 miles per hour — as calculated by the mission team — making it the fastest-ever human-made object relative to the Sun. This breaks the record set by the German-American Helios 2 mission in April 1976.

Parker Solar Probe will repeatedly break its own records, achieving a top speed of about 430,000 miles per hour in 2024.

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NASA release
Parker Solar Probe Reports Good Status After Close Solar Approach

Parker Solar Probe is alive and well after skimming by the Sun at just 15 million miles from our star's surface. This is far closer than any spacecraft has ever gone — the previous record was set by Helios B in 1976 and broken by Parker on Oct. 29 — and this maneuver has exposed the spacecraft to intense heat and solar radiation in a complex solar wind environment.

"Parker Solar Probe was designed to take care of itself and its precious payload during this close approach, with no control from us on Earth — and now we know it succeeded," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate at the agency headquarters in Washington. "Parker is the culmination of six decades of scientific progress. Now, we have realized humanity's first close visit to our star, which will have implications not just here on Earth, but for a deeper understanding of our universe."

Mission controllers at the Johns Hopkins University Applied Physics Lab received the status beacon from the spacecraft at 4:46 p.m. EST on Nov. 7, 2018. The beacon indicates status "A" — the best of all four possible status signals, meaning that Parker Solar Probe is operating well with all instruments running and collecting science data and, if there were any minor issues, they were resolved autonomously by the spacecraft.

At its closest approach on Nov. 5, called perihelion, Parker Solar Probe reached a top speed of 213,200 miles per hour, setting a new record for spacecraft speed. Along with new records for the closest approach to the Sun, Parker Solar Probe will repeatedly break its own speed record as its orbit draws closer to the star and the spacecraft travels faster and faster at perihelion.

At this distance, the intense sunlight heated the Sun-facing side of Parker Solar Probe's heat shield, called the Thermal Protection System, to about 820 degrees Fahrenheit. This temperature will climb up to 2,500 F as the spacecraft makes closer approaches to the Sun — but all the while, the spacecraft instruments and systems that are protected by the heat shield are generally kept in the mid-80s F.

Parker Solar Probe's first solar encounter phase began on Oct. 31, and the spacecraft will continue collecting science data through the end of the solar encounter phase on Nov. 11. It will be several weeks after the end of the solar encounter phase before the science data begins downlinking to Earth.

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Johns Hopkins Applied Physics Laboratory release
Parker Solar Probe Completes Download of Science Data from First Two Solar Encounters

As NASA's Parker Solar Probe approaches its third encounter with the Sun, mission scientists are hard at work poring over data from the spacecraft's first two flybys of our star — and thanks to excellent performance by the spacecraft and the mission operations team, they're about to get something extra.

On May 6, 2019, just over a month after Parker Solar Probe completed its second solar encounter, the final transmission of 22 gigabytes of planned science data — collected during the first two encounters — was downlinked by the mission team at the Johns Hopkins Applied Physics Laboratory, or APL, in Laurel, Maryland.

This 22 GB is 50% more data than the team had estimated would be downlinked by this point in the mission — all because the spacecraft's telecommunications system is performing better than pre-launch estimates. After characterizing the spacecraft's operations during the commissioning phase, which began soon after launch, the Parker mission team determined that the telecom system could effectively deliver more downlink opportunities, helping the team maximize the download of science data.

The team has capitalized on the higher downlink rate, instructing Parker Solar Probe to record and send back extra science data gathered during its second solar encounter. This additional 25 GB of science data will be downlinked to Earth between July 24 and Aug. 15.


"All of the expected science data collected through the first and second encounters is now on the ground," said Nickalaus Pinkine, Parker Solar Probe mission operations manager at APL. "As we learned more about operating in this environment and these orbits, the team did a great job of increasing data downloads of the information gathered by the spacecraft's amazing instruments."

There are four instrument suites on Parker, gathering data on particles, waves, and fields related to the Sun's corona and the solar environment. Scientists use this information — gathered closer to the Sun than any previous measurements — along with data from other satellites and scientific models to expand on what we currently know about the Sun and how it behaves. Data collected during the first two perihelia will be made available to the public later this year.



Parker Solar Probe continues on its record-breaking exploration of the Sun with its third solar encounter beginning Aug. 27, 2019; the spacecraft's third perihelion will occur on Sept. 1.

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NASA release
First NASA Parker Solar Probe Results Reveal Surprising Details About Our Sun

The Sun is revealing itself in dramatic detail and shedding light on how other stars may form and behave throughout the universe – all thanks to NASA's Parker Solar Probe. The spacecraft is enduring scorching temperatures to gather data, which are being shared for the first time in four new papers that illuminate previously unknown and only-theorized characteristics of our volatile celestial neighbor.

Above: The WISPR image on NASA's Parker Solar Probe captured imagery of the constant outflow of material from the Sun during its close approach to the Sun in April 2019. (NASA/NRL/APL)

The information Parker has uncovered about how the Sun constantly ejects material and energy will help scientists rewrite the models they use to understand and predict the space weather around our planet, and understand the process by which stars are created and evolve. This information will be vital to protecting astronauts and technology in space – an important part of NASA's Artemis program, which will send the first woman and the next man to the Moon by 2024 and, eventually, on to Mars.

The four papers, now available online from the journal Nature, describe Parker's unprecedented near-Sun observations through two record-breaking close flybys. They reveal new insights into the processes that drive the solar wind – the constant outflow of hot, ionized gas that streams outward from the Sun and fills up the solar system – and how the solar wind couples with solar rotation. Through these flybys, the mission also has examined the dust of the coronal environment, and spotted particle acceleration events so small that they are undetectable from Earth, which is nearly 93 million miles from the Sun.

During its initial flybys, Parker studied the Sun from a distance of about 15 million miles. That is already closer to the Sun than Mercury, but the spacecraft will get even closer in the future, as it travels at more than 213,000 mph, faster than any previous spacecraft.

"This first data from Parker reveals our star, the Sun, in new and surprising ways," said Thomas Zurbuchen, associate administrator for science at NASA Headquarters in Washington. "Observing the Sun up close rather than from a much greater distance is giving us an unprecedented view into important solar phenomena and how they affect us on Earth, and gives us new insights relevant to the understanding of active stars across galaxies. It's just the beginning of an incredibly exciting time for heliophysics with Parker at the vanguard of new discoveries."

Among the findings are new understandings of how the Sun's constant outflow of solar wind behaves. Seen near Earth, the solar wind plasma appears to be a relatively uniform flow – one that can interact with our planet's natural magnetic field and cause space weather effects that interfere with technology. Instead of that flow, near the Sun, Parker's observations reveal a dynamic and highly structured system, similar to that of an estuary that serves as a transition zone as a river flows into the ocean. For the first time, scientists are able to study the solar wind from its source, the Sun's corona, similar to how one might observe the stream that serves as the source of a river. This provides a much different perspective as compared to studying the solar wind were its flow impacts Earth.

Switchbacks

One type of event in particular caught the attention of the science teams – flips in the direction of the magnetic field, which flows out from the Sun, embedded in the solar wind and detected by the FIELDS instrument. These reversals – dubbed "switchbacks" – appear to be a very common phenomenon in the solar wind flow inside the orbit of Mercury, and last anywhere from a few seconds to several minutes as they flow over the spacecraft. Yet they seem not to be present any farther from the Sun, making them undetectable without flying directly through that solar wind the way Parker has.

During a switchback, the magnetic field whips back on itself until it is pointed almost directly back at the Sun. These switchbacks, along with other observations of the solar wind, may provide early clues about what mechanisms heat and accelerate the solar wind. Not only does such information help change our understanding of what causes the solar wind and space weather affecting Earth, it also helps us understand a fundamental process of how stars work and how they release magnetic energy into their environment.

Rotating Wind

In a separate publication, based on measurements by the Solar Wind Electrons Alphas and Protons (SWEAP) instrument, researchers found surprising clues as to how the Sun's rotation affects the outflow of the solar wind. Near Earth, the solar wind flows past our planet as if it travels initially in almost straight lines – or "radially," like spokes on a bicycle wheel – out from the Sun in all directions. But the Sun rotates as it releases the solar wind, and before it breaks free, the solar wind is expected to get a push in sync with the Sun's rotation.

As Parker ventured to a distance of around 20 million miles from the Sun, researchers obtained their first observations of this effect. Here, the extent of this sideways motion was much stronger than predicted, but it also transitioned more quickly than predicted to a straight, strictly outward flow, which helps mask the effects at a larger distance. This enormous extended atmosphere of the Sun will naturally affect the star's rotation. Understanding this transition point in the solar wind is key to helping us understand how the Sun's rotation slows down over time, with implications for the lifecycles of our star, its potentially violent past, as well as other stars and the formation of protoplanetary disks, dense disks of gas and dust encircling young stars.

Dust in the Wind

Parker also observed the first direct evidence of dust starting to thin out around 7 million miles from the Sun – an effect that has been theorized for nearly a century, but has been impossible to measure until now. These observations were made using Parker's Wide-field Imager for Solar Probe (WISPR) instrument, at a distance of about 4 million miles from the Sun. Scientists have long suspected that close to the Sun, this dust would be heated to high temperatures, turning it into a gas and creating a dust-free region around the star. At the observed rate of thinning, scientists expect to see a truly dust-free zone beginning at a distance of about 2-3 million miles from the Sun, which the spacecraft could observe as early as September 2020, during its sixth flyby. That dust-free zone would signal a place where the material of the dust has been evaporated by the Sun's heat, to become part of the solar wind flying past Earth.

Energetic Particles

Finally, Parker's Integrated Science Investigation of the Sun (ISʘIS) energetic particle instruments have measured several never-before-seen events so small that all traces of them are lost before they reach Earth. These instruments have also measured a rare type of particle burst with a particularly high ratio of heavier elements – suggesting that both types of events may be more common than scientists previously thought. Solar energetic particle events are important, as they can arise suddenly and lead to space weather conditions near Earth that can be potentially harmful to astronauts. Unraveling the sources, acceleration and transport of solar energetic particles will help us better protect humans in space in the future.

"The Sun is the only star we can examine this closely," said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. "Getting data at the source already is revolutionizing our understanding of our own star and stars across the universe. Our little spacecraft is soldiering through brutal conditions to send home startling and exciting revelations."

Data from Parker Solar Probe's first two solar encounters are available online here.

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NASA release
Parker Solar Probe Prepares for Third Venus Flyby

Coming off its fifth encounter with the Sun — and the mission's longest observation campaign yet — Parker Solar Probe is now headed toward Venus.

Above: Parker Solar Probe performs its third Venus flyby on July 11, 2020 (UTC), setting the spacecraft up for another record-breaking close approach to the Sun in September 2020. (NASA/Johns Hopkins APL/Steve Gribben)

Early on July 11, 2020 (UTC), the spacecraft will perform its first outbound flyby of Venus, passing approximately 516 miles above the surface as it curves around the planet. Such Venus gravity assists play an integral role in the Parker Solar Probe mission. The spacecraft relies on the planet to rid itself of orbital energy, which in turn allows it to travel ever closer to the Sun after each Venus flyby. The mission's previous two Venus flybys swooped past the Sun-facing side of the planet, and this will be Parker Solar Probe's first pass on Venus' night side.

Parker Solar Probe will witness a brief 11-minute solar eclipse during the maneuver while passing through the shadow of the planet. Utilizing powerful telescopes, the Apache Point Observatory in New Mexico, Lick Observatory in California, and the Keck Observatory in Hawaii will search for Venus aurora from the ground in coordination with Parker Solar Probe's pass around the planet, weather permitting. Scientists will combine these ground-based observations with data collected by Parker Solar Probe during the flyby to take an unprecedented look at the interactions between Venus and the solar wind.

This Venus flyby sets Parker Solar Probe up for its sixth close pass by the Sun, slated for September 27. During this perihelion, Parker Solar Probe will travel even closer to the Sun, setting a new record when it passes approximately 8.3 million miles from the solar surface, more than 3 million miles closer than the previous perihelion at 11.6 million miles from the solar surface. The spacecraft's seventh perihelion is slated for January 17, 2021.

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NASA release
NASA Enters the Solar Atmosphere for the First Time, Bringing New Discoveries

For the first time in history, a spacecraft has touched the Sun. NASA's Parker Solar Probe has now flown through the Sun's upper atmosphere – the corona – and sampled particles and magnetic fields there.

The new milestone marks one major step for Parker Solar Probe and one giant leap for solar science. Just as landing on the Moon allowed scientists to understand how it was formed, 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.

"Parker Solar Probe "touching the Sun" is a monumental moment for solar science and a truly remarkable feat," said Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "Not only does this milestone provide us with deeper insights into our Sun's evolution and it's impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe."

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. 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.

The first passage through the corona – and the promise of more flybys to come – will continue to provide data on phenomena that are impossible to study from afar.

"Flying so close to the Sun, Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere – the corona – that we never could before," said Nour Raouafi, the Parker project scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. "We see evidence of being in the corona in magnetic field data, solar wind data, and visually in images. We can actually see the spacecraft flying through coronal structures that can be observed during a total solar eclipse."

Closer Than Ever Before

Parker Solar Probe launched in 2018 to explore the mysteries of the Sun by traveling closer to it than any spacecraft before. Three years after launch and decades after first conception, Parker has finally arrived.

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.

That point, known as 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. Importantly, 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.

Until now, researchers were unsure exactly where the Alfvén critical surface lay. 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 – if the estimates were correct.

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.

"We were fully expecting that, sooner or later, we would encounter the corona for at least a short duration of time," said Justin Kasper, lead author on a new paper about the milestone published in Physical Review Letters, and deputy chief technology officer at BWX Technologies, Inc. and University of Michigan professor. "But it is very exciting that we've already reached it."

Into the Eye of the Storm

During the flyby, 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.

Above: As Parker Solar Probe passed through the corona on encounter nine, the spacecraft flew by structures called coronal streamers. These structures can be seen as bright features moving upward in the upper images and angled downward in the lower row. (NASA/Johns Hopkins APL/Naval Research Laboratory)

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.

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.

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.

The first passage through the corona, which lasted only a few hours, is one of many planned for the mission. 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.

"I'm excited to see what Parker finds as it repeatedly passes through the corona in the years to come," said Nicola Fox, division director for the Heliophysics Division at NASA Headquarters. "The opportunity for new discoveries is boundless."

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.

"It is a really important region to get into because we think all sorts of physics potentially turn on," Kasper said. "And now we're getting into that region and hopefully going to start seeing some of these physics and behaviors."

Narrowing Down Switchback Origins

Even before the first trips through the corona, some surprising physics was already surfacing. 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.

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. 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.

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?

The new findings, in press at the Astrophysical Journal, finally confirm one origin point is near the solar surface.

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. 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.

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.

"The structure of the regions with switchbacks matches up with a small magnetic funnel structure at the base of the corona," said Stuart Bale, professor at the University of California, Berkeley, and lead author on the new switchbacks paper. "This is what we expect from some theories, and this pinpoints a source for the solar wind itself."

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.

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.

"My instinct is, as we go deeper into the mission and lower and closer to the Sun, we're going to learn more about how magnetic funnels are connected to the switchbacks," Bale said. "And hopefully resolve the question of what process makes them."

Above: As Parker Solar Probe ventures closer to the Sun, it's crossing into uncharted regimes and making new discoveries. This image represents Parker Solar Probe's distances from the Sun for some of these milestones and discoveries. (NASA's Goddard Space Flight Center/Mary P. Hrybyk-Keith)

Now that researchers know what to look for, Parker's closer passes may reveal even more clues about switchbacks and other solar phenomena. The data to come will allow scientists a glimpse into a region that's critical for superheating the corona and pushing the solar wind to supersonic speeds. Such measurements from the corona will be critical for understanding and forecasting extreme space weather events that can disrupt telecommunications and damage satellites around Earth.

"It's really exciting to see our advanced technologies succeed in taking Parker Solar Probe closer to the Sun than we've ever been, and to be able to return such amazing science," said Joseph Smith, Parker program executive at NASA Headquarters. "We look forward to seeing what else the mission discovers as it ventures even closer in the coming years."

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Ultimate Bulletin Board 5.47a





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