NASA’s fastest, farthest sun mission
Photos by Evan Krape and courtesy of NASA | Video and photo illustration by Jeffrey Chase July 15, 2019
UD physicist William Matthaeus helped lay the foundation for the Parker Solar Probe
Editor's note: This story was first published in August 2018.
It’s not easy to be a student of the sun. Your subject is roughly 93 million miles away. You can’t go there because you don’t have that kind of ride. You can’t look at it because you’d go blind. You can’t touch it because you’d be incinerated long before you got close. And you can’t get close because it is surrounded by high-velocity streams of hot plasma emanating from all directions. Even if you found a way to get into that firehose of plasma, some of it reaching speeds of 1.8 million miles per hour, you would experience such chaotic turbulence that you would want to go anywhere else – fast.
This thing we call the sun is mysterious in all its ways.
But if you want to study it, as NASA most definitely does, it’s a great idea to have the University of Delaware’s William Matthaeus, Unidel Professor of Physics and Astronomy, at the drawing board. As a space plasma physicist, he thinks about some of the most intangible questions ever raised. He calculates how things would work and interact according to the laws of physics as we understand them. He would help you figure out if this study was worth all the brainpower and effort and money it would require.
He has done that kind of thinking for NASA, which recently launched its most ambitious sun-related mission ever – the Parker Solar Probe Mission – from Cape Canaveral, Fla. Matthaeus was part of the Science and Technology Definition Team that informed the plans for this mission, which will send a spacecraft into the hot plasma of the sun’s corona for the first time. The corona is the outermost edge of the sun’s atmosphere.
The launch date changed several times, but everything came together on Sunday, Aug. 12. The mission had to go by Aug. 19, astronomers said, because of its reliance on a certain interaction with Venus and the impact that interaction has on its velocity and energy consumption.
Matthaeus, who has been on UD’s faculty since 1983 and also is director of the Delaware Space Grant program, hopes to be present with several UD colleagues, postdoctoral researchers and students to witness the launch of the car-sized spacecraft that is meant to orbit the sun for at least the next seven years.
“The first step was designing the heat shields and thermal control systems,” Matthaeus said. “The technology has made it feasible for the last 10 years or so, but we’re finally going to do it. And the little state of Delaware has a little piece of a billion-dollar mission.”
Zooming at speeds that will exceed 400,000 miles per hour, the Parker Solar Probe (called PSP for short) will be the fastest spacecraft ever and get within 4 million miles of the sun – more than five times closer than the previous record set by the Helios-B spacecraft, which got about 27 million miles away.
It will provide our first glimpse of several regions of the solar wind – the powerful streams of scorching plasma coming from the sun’s corona – and help us understand more about how things work in the sun’s atmosphere and beyond. That, in turn, will help us understand how the sun changes the space environment, where space weather affects astronauts, satellites, electronics and, for the strongest events, even electric power grids on the Earth’s surface.
The Solar Probe will test calculations and predictions made over the past six decades since University of Chicago physicist Eugene Parker first theorized about the solar wind.
And it may help to answer significant questions that have puzzled scientists for decades.
One major question deals with the counterintuitive fact that the lower corona, where solar wind is born, is far hotter than the surface of the sun. The corona, the part that is visible in a total eclipse, can reach temperatures approaching several million degrees Fahrenheit. The surface of the sun is about 10,000 degrees Fahrenheit.
Rohit Chhiber, who recently earned his doctorate and is a student of Matthaeus, spent long hours calculating conditions the spacecraft may encounter at three important stages of its journey through the solar wind. That study was the crux of his dissertation and he was the lead author of an article for Astrophysical Journal that reported on the model he created.
Three landmarks of great interest include:
The point (closest to the sun) at which the solar wind reaches supersonic speed.
The point at which the solar wind reaches super-Alfvenic speed (the speed of magnetic waves).
The point at which the solar wind reaches the beta-1 location (where the mechanical pressure equals the magnetic pressure). When the solar wind passes this point, the sun’s magnetic fields no longer dominate and govern its motion.
“When the wind passes these points and exceeds these speed thresholds, the magnetic field starts to curve away in a spiral,” Matthaeus said. “So we’re very interested to see what happens when the Parker Solar Probe passes through these regions. We’re trying to find out why the solar wind is here, how it is heated and propelled.”
UD’s Bennett Maruca, assistant professor of physics and astronomy, has a keen interest in the mission, too. His thesis advisor – Justin Kasper, formerly of the Harvard-Smithsonian Center for Astrophysics and now at the University of Michigan – made the only instrument that will be outside the spacecraft, encountering the intense elements without a heat shield.
Chhiber and NASA research scientist Arcadi Usmanov created a video simulation of these calculations to show how PSP’s orbits are likely to unfold. Each orbit takes about 100 days and the spacecraft is expected to make 33 orbits. The spacecraft’s sensors will collect data that will be transmitted to Earth as the mission unfolds.
“Every orbit it records the data from the instruments and at a certain point that data goes to big antennas that use microwave transmissions from the spacecraft to receive information from the onboard instruments,” Matthaeus said. “There are times when it is absolutely impossible to send anything back because of this big object in the way.”
When it’s on the far side of the sun, that is.
Chhiber has analyzed the character of gas dynamics and changes in plasma dynamics across these regions and has made estimates of the conditions that will be encountered.
“The amount of time PSP spends in different regions tells you the kind of science you’ll be discovering in those different regions,” Matthaeus said.
Matthaeus, UD colleague and Professor Michael Shay and research associate Tulasi Parashar shared some of their studies of the heliosphere and the magnetosphere during workshops at the SHINE (Solar Heliospheric & Interplanetary Environment) Conference, held in Cocoa Beach, Florida., in late July.
NASA photos courtesy of NASA/Johns Hopkins APL/Ed Whitman, ESA&NASA/SOHO and APL/NASA/Goddard Space Flight Center.