Parker Solar Probe: The Science of 'Touching the Sun'

In only a few days, NASA’s Parker Solar Probe will be launched to “Touch the Sun.” Image Credit: NASA

With the upcoming launch of NASA’s Parker Solar Probe (PSP) scientists are about to reach out and “touch the Sun” for the first time ever. The probe will fly through the incredibly hostile atmosphere of the Sun, where it will study the physics behind how heat and energy flow through the atmosphere, and also aim to better understand the solar wind, which can bring down our power grids and cripple satellites, as well as give us fantastic displays of the Aurora Borealis.

PSP is scheduled to launch on Aug. 11, 2018 at 3:33 a.m. EDT, at the opening of a 65-minute window, and the weather forecast from the U.S. Air Force 45th Space Wing expects an 80% chance of favorable conditions for liftoff. The launch window shifts 2 minutes earlier each day after as well, should the launch delay beyond Aug 11.

 

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The spacecraft is now encapsulated in a bullet-like payload fairing and attached atop its giant rocket, the 232-foot tall (70.7m) United Launch Alliance (ULA) Delta-IV Heavy, the largest and most powerful rocket currently used by NASA (see the photos here). But the launch window only extends to August 23; PSP must launch by then in order to swing by Venus, whose gravity the spacecraft will need to “steer” itself into the proper orbits of the Sun for the mission’s science objectives. Each orbit will get closer to the Sun than the previous one.

If it doesn’t, it will have to wait until May 2019 to try again, when Venus is in the needed position again.

PSP was built by the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland and is the most autonomous spacecraft ever made. It will also become the fastest human-made object in history when it makes its closest approach to the Sun, traveling at speeds of up to 430,000 miles per hour (700,000 kilometers per hour) as it swoops through the Sun’s “atmosphere” (corona) 24 times over a period of 7 years. That’s as fast as traveling from New York City to Tokyo in less than one minute. At closest approach to the Sun in 2024, PSP will be only four-and-a-half solar diameters, or 3.8 million miles, above the solar surface.

The sun’s corona shines bright in this incredible image of a Total Solar Eclipse over South Carolina, USA on August 21, 2017. NASA’s Parker Solar Probe will dive through this region numerous times over the next 7 years, giving humanity our first ever samplings of a star, and a better understanding of how it works and drives the space environment across the Solar System. Photo Credit: Hap Griffin / www.ImagingInfinity.com

On June 27, 2018, the probe’s heat shield, called the Thermal Protection System (TPS) was installed. The shield is eight feet in diameter, weighs about 160 pounds and is made of two panels of superheated carbon-carbon composite sandwiching a lightweight 4.5-inch-thick carbon foam core; it is designed to endure the extreme heat that PSP will encounter, of nearly 2,500 degrees Fahrenheit (1,377 degrees Celsius).

“Parker Solar Probe is going to revolutionize our understanding of the Sun, the only star we can study up close,” said Nicola Fox, project scientist for Parker Solar Probe at the Johns Hopkins Applied Physics Lab in Laurel, Maryland.

“This is a piece of heliophysics science we all really wanted for a long time, since the 1950s,” said Stuart Bale, a UC Berkeley professor of physics, former director of the campus’s Space Sciences Laboratory and one of four principal investigators for the instruments aboard the mission. “For me personally, I’ve been working on the probe since it was approved in 2010, but I really spent a large part of my career getting ready for it.”

Speaking of science objectives, what are the main science goals for the PSP mission? Overall, they include:

  • Trace the flow of energy that heats and accelerates the solar corona and solar wind.
  • Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind.
  • Explore mechanisms that accelerate and transport energetic particles.

PSP will actually penetrate the corona (which you can see during total solar eclipses), taking many different kinds of measurements with four instrument suites, producing images to help revolutionize scientists’ understanding of how the Sun, and therefore other stars as well, behave. Never before has any spacecraft ever come so close to the Sun, but it is necessary for PSP to be able to take the needed measurements. But why do scientists want to study the Sun anyway? There are many good reasons:

  • The Sun is the only star we can study up close. By studying this star we live with, we learn more about stars throughout the Universe.
  • The Sun is a source of light and heat for life on Earth. The more we know about it, the more we can understand how life on Earth developed.
  • The Sun also affects Earth in less familiar ways. It is the source of the solar wind; a flow of ionized gases from the Sun that streams past Earth at speeds of more than 500 km per second (a million miles per hour).
  • Disturbances in the solar wind shake Earth’s magnetic field and pump energy into the radiation belts, part of a set of changes in near-Earth space known as space weather.
  • Space weather can change the orbits of satellites, shorten their lifetimes, or interfere with onboard electronics. The more we learn about what causes space weather – and how to predict it – the more we can protect the satellites we depend on.
  • The solar wind also fills up much of the Solar System, dominating the space environment far past Earth. As we send spacecraft and astronauts further and further from home, we must understand this space environment just as early seafarers needed to understand the ocean.

The Sun is the closest star to Earth, and soon, the Parker Solar Probe will become the first spacecraft to study it up close. Photo Credit: NASA/SDO

Space weather effects such as solar wind, flares and coronal mass ejections are some of the most important reasons, since they can adversely affect satellite communications and the power grid on Earth. This knowledge can also help with issues like pipeline erosion, radiation exposure on airline flights and astronaut safety.

Apart from the safety concerns, scientists have been trying to answer some of the big questions about the Sun for over 60 years now, such as how energy and heat move through the solar corona and what accelerates the solar wind and solar energetic particles. But to get the answers, it is necessary to actually fly through the corona itself. Another big question is the “coronal heating problem” – the apparent mismatch between the temperature of the Sun’s photosphere – the “surface,” measuring about 10,000 degrees Fahrenheit – and the much higher temperature of the corona – the “atmosphere,” about 1.7 million degrees Fahrenheit (and can reach 10 million degrees Fahrenheit). Why are ions and electrons in the corona so much hotter than the Sun’s surface?

FIELDS is one of the instrument packages on PSP. It will measure the electric and magnetic fields in the corona to determine the total amount of energy streaming outward from the Sun, utilizing a six-foot boom projecting from the spacecraft in the direction that PSP is moving.

Scientists can use the results from FIELDS to test one theory: that the Sun heats the corona by jiggling the magnetic field lines. The magnetic field lines are anchored on the Sun’s surface, but constantly move around due to convection below the surface. This movement creates “waves,” called Alfvén waves, which move outward along the lines. The waves then accelerate particles to high speeds and fling them out into space.

Illustration of the orbit of PSP around the Sun. PSP will swoop through the Sun’s “atmosphere” (corona) 24 times over a period of 7 years. Image Credit: NASA’s Scientific Visualization Studio

“If the wave-driven model is correct, then I think our measurements will be the fundamental measurements on the mission,” Bale said.

The other main theory is that tiny flares called nanoflares, all over the surface of the Sun, produce magnetic fields that cross, reconnect and fling disconnected loops of magnetic field into space, thereby accelerating ions as well. This theory was actually first proposed in 1987 by Eugene Parker, after whom PSP is named. Radio antennas, part of the FIELDS package, will look for radio waves created by nanoflares, while another package of instruments, SWEAP (Solar Wind Electrons Alphas and Protons), will record the speed of solar wind electrons, protons and alpha particles.

Will one of those theories be proven correct, or might there be some other explanation? Only PSP can help answer that question.

There are also two other instrument packages – WISPR, the Wide-Field Imager for Parker Solar Probe and ISʘIS (pronounced E-sis), Integrated Science Investigation of the Sun, which includes includes ʘ, the symbol for the Sun, in its acronym. WISPR will capture visible-light images of the Sun’s corona, while ISʘIS will measure the energy and identity of energized electrons and ions, including ions heavier that hydrogen and helium. This will help scientists figure out how they are sometimes accelerated to nearly the speed of light, close to the Sun.

“Plasma physics is really hard to study in the laboratory,” said Bale, who focuses on the role of magnetic fields and ionized plasma in space, in particular around stars like the Sun. “Sticking a spacecraft right in the hot plasma makes an ideal laboratory.”

Artist’s conception of Earth-sized exoplanet Kepler-452b. PSP will also help scientists better understand how other Sun-like stars behave and affect the habitability of ny planets that orbit them. Image Credit: NASA Ames/JPL-Caltech/T. Pyle

PSP will reach its first close encounter with the Sun in November, after looping around Venus and using its gravity to slow down. During this first approach, PSP will reach a distance from the center of the Sun equal to 36 times the Sun’s radius (36 solar radii). By comparison, Venus orbits at 155 solar radii and Mercury at 83 solar radii. Eventually, over the next 6 years, PSP will come to within 9.8 solar radii, where it will be at the outer edge of the region in which particles exceed the speed of sound – the Alfvén speed, about 200 miles per second.

“The goal of the mission is to get inside that transition region, so we get into the real corona where the flow is subAlfvénic,” Bale said. “We think that boundary is at about 15 solar radii, so we probably won’t start hitting it until 2021.”

“In early December, I am counting on having that first pass of data at 35 solar radii, and I am sure it will be revolutionary. There will be great new stuff in there, from what we know about previous missions,” Bale added.

Parker Solar Probe sits in a clean room on July 6, 2018, at Astrotech Space Operations in Titusville, Florida, after the installation of its heat shield. Photo Credit: NASA/Johns Hopkins APL/Ed Whitman

Beyond just our own Sun, PSP will also help scientists extrapolate that knowledge to learn more about other Sun-like stars, and conditions for possible habitability of any planets orbiting those stars. Such stars are common in our galaxy, and thanks to Kepler and other telescopes, we already know about exoplanets orbiting many of them, including Earth-sized worlds in the habitable zones of their stars (where temperatures could allow liquid water on their surfaces). If scientists can better understand how the behavior of our own Sun affected the development of life on Earth, they can then fine-tune their search for possible biomarkers on planets orbiting other stars as well, in particular stars similar in size, age and composition to the Sun.

NASA will also be holding a series of media briefings about the mission beginning August 8.

Soon now, the Parker Solar Probe will launch to the Sun, coming much closer than any previous mission. Continue to follow AmericaSpace during the course of this exciting mission – the first-ever spacecraft sent to ‘Touch the Sun.”

 


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