How the sun does what it does
Photos and photo illustration by Kathy F. Atkinson and courtesy of NASA's Goddard Space Flight Center February 07, 2020
UD researchers offer glimpse into what NASA’s Parker Solar Probe is showing us
Powerful things are happening constantly in the enormous stretch of space over our heads and researchers are tapping into a powerful new source of information — NASA’s Parker Solar Probe — to learn more about the sun and its fiery, roiling atmosphere.
The Parker Solar Probe (PSP for short) is a car-sized spacecraft launched by NASA in 2018, the fastest human-made object ever built. It is designed to collect and transmit data from deep within the sun’s atmosphere. Already it has gone closer to the sun than any other spacecraft and it will periodically break its own record as its orbits tighten to within four million miles of the sun. It has completed four of the 24 solar encounters expected during its seven-year mission.
The Astrophysical Journal Supplement Series has just published a special issue focused on early findings from the PSP. Five of the articles included were written by University of Delaware researchers, alumni and affiliates. The authors include William H. Matthaeus, Unidel Professor of Physics and Astronomy, Bennett A. Maruca, assistant professor of physics and astronomy, postdoctoral researcher Rohit Chhiber, research associate Tulasi N. Parashar and graduate students Riddhi Bandyopadhyay and Ramiz A. Qudsi.
Matthaeus, who is also director of the Delaware Space Grant Consortium, was among the theoretical physicists who helped NASA design the PSP mission concept. On Sunday, Feb. 9, he plans to be in Cape Canaveral, Florida, for the planned launch of the European Space Agency’s Solar Orbiter, for which he is also a co-investigator of the magnetometer. Solar Orbiter will explore the polar regions of the sun, where magnetic forces are the greatest, collecting data that will complement the data PSP is now returning.
“We’re trying to understand the fundamental physics that makes the heliosphere work,” said Matthaeus, referring to the region in space influenced by the sun or solar wind. “There are more practical problems people work on — like space weather — when they want to do predictions. But the prediction will fail if you don’t understand the fundamental science that’s going on. The predictions would be guesses, really…. A lot of what we’re doing has to do with the distinction between processes that are uniform and homogeneous and those that are highly intermittent or patchy in space.”
Among the questions addressed in this “PSP Fest” — as the UD team calls it:
Efforts to quantify turbulence and its role in transferring heat and energy in the plasma
Measurements of the rate at which energy is moving across these scales
Calculations related to many structures and dynamics, including Alfvénic waves (the way charged particles oscillate in magnetic fields) and magnetic flux tubes associated with specific regions of the sun
Matthaeus said the team hopes one day to be able to trace these observations to their source regions in the sun by using computer models being developed by UD associates Arcadi Usmanov and Chhiber, both of whom work at NASA’s Goddard Space Flight Center. Those models provide three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind, the highly energized stream of particles flowing out from the sun.
“There has been a clear sense from the beginning that this is historic,” said Maruca. “The Voyager spacecraft were launched in the 70’s and we’re still analyzing their data. The Helios spacecraft were launched in the 70’s and we’re still analyzing data from them. People will be analyzing Parker Solar Probe data 50 years from now…. Having a connection to that future heritage — we’re going to be part of someone else’s scientific heritage.”
It is exciting to be among the first to see and analyze this data, said Qudsi, a doctoral student working with Maruca and a first author of one of the articles.
“The most exciting thing for me was being on the forefront of it — we literally got to see this data for the first time along with everyone,” he said. “It was surreal. No one else has seen this. I’m one of about 50 or 100 people on Earth looking at this data. That was a different kind of feeling. It was really great to have that opportunity.”
Riddhi Bandyopadhyay, first author of two of the articles and Matthaeus’ doctoral student, has been looking at the heating rate and charged-particle acceleration of the “young” solar wind — the solar wind measured closest to the sun’s surface.
“It surprised me that the young solar wind is not that young,” he said. “It seemed pretty much already developed, with enhanced turbulent heating.”
There is much more to come from these regions that have never before been explored at such close range, Maruca said.
“It’s all new,” he said. “We are just scratching the surface and already are extending our understanding of what is happening here, trying to see how things much closer to the sun compared to their behaviors out here. A lot of it is the same, but a lot of it isn’t — the specific processes that go on, the conditions we’re encountering are unlike anything we could even conceive of reproducing in a laboratory. It’s far hotter, far less dense.”
There have been some big surprises, as other articles have explained.
For example, “nobody was really predicting the switchbacks,” Maruca said. Switchbacks are wrinkle-like turns in magnetic field lines, which change direction and hold a lot of energy. The spacecraft flies through that, but its trajectory is not affected.
“But what generates a switchback and why is it generated?” Maruca said. “What happens to it? It’s a new piece of the puzzle in understanding coronal heating. What is the physical process that ultimately brings it into the heliosphere?”
Most of us can’t even come up with the questions physicists deal with routinely, let alone try to answer them. But the puzzle of coronal heating is a long-standing question that even non-physicists can grasp. Why is the sun’s corona — its outer atmosphere, which can be seen during a solar eclipse — millions of degrees hotter than the sun’s surface?
If you stood two feet away from a blazing fire in a fireplace you would correctly expect to be much hotter there than if you were 20 feet from the same fireplace. That’s why this phenomenon is so strange.
Such answers lie in the mechanics and electro-dynamics of the systems in play, factors that may be more precisely revealed by PSP as it provides a vantage point far closer to the sun than ever achieved.
Conditions in this area are extraordinary. For example, the solar wind has an enormous range of wavelength sizes, Matthaeus said. Some features are as large as 100 times the distance from the sun to the Earth, some as small as the length of Fairfax Shopping Center in Delaware — about a kilometer, he said.
And everything in its mix can affect how these phenomena work and how they interact with other structures and plasma dynamics.
“Why can’t we predict the weather more accurately?” Maruca said. “Everything is relevant from the size of weather patterns and the thunderstorms to the size of a drop of water and a speck of dust. When you’re trying to understand how energy moves from one scale to another — that’s what we’re trying to do here…. What happens to the solar wind on its way to us?”
Much more information is on the way.
By The Numbers
Parker Solar Probe by the numbers:
93 million miles = the distance the sun is from Earth
3.9 million miles = the closest PSP can get to the sun
109 = the number of Earths lined up end-to-end to cover the diameter of the sun
430,000 mph = the maximum speed of the PSP, fast enough to go from Washington to Philadelphia in 1 second
2,500 degrees Fahrenheit = the heat that will test the PSP’s solar shield when it is closest to the sun. Inside the spacecraft, the payload remains at room temperature
$2 billion = the cost of the PSP mission