Michigan Engineering News

For a precious few minutes on April 8, 2024, observers of the total solar eclipse will see the sun as scientists know it: not as a steady ball of light, but as a dynamic star, rich with detail, variety and complexity. The sun will reveal its outermost atmosphere in a stunning lightshow. Intense rays of light will stretch into space while others loop back toward the solar surface and outline the moon’s shadow like a crown—a view that inspired the outer atmosphere’s latin name: corona.

The eclipse is a high-water mark for NASA’s Heliophysics Big Year, a global celebration of solar science that takes place between October 2023 and December 2024. Millions will flock into its path.

For University of Michigan researchers who have dedicated their careers to building a better understanding of the sun, the eclipse holds a different allure: the chance to gather scientific data that’s normally overshadowed by the sun’s blinding light in the visible spectrum and the constant buzz of radio noise at longer electromagnetic wavelengths. It’s also a unique opportunity to get budding young scientists and others involved in the study of the sun and its impact on the solar system and our planet, or heliophysics. Students and other groups will complement scientists’ efforts to observe the sun with antennas that measure the sun’s radiation and photos that could uncover new information during the eclipse.

The sun is made of layers of electrically conductive gas, or plasma. The hottest and densest plasma is at the sun’s core and the surrounding layers get progressively cooler and thinner, eventually becoming so thin that scientists consider the outer layers to be an atmosphere.

The corona, however, doesn’t follow the same rules as the rest of the sun. In fact, it doesn’t even follow the rules of basic physics. It’s nearly 200 times hotter than the sun’s surface despite being farther from the heat source at the core. The corona is so searing that its plasma moves fast enough to escape the sun’s gravity and stream away at supersonic speeds. This plasma sparks the impressive rays and loops that will be visible from the ground during the eclipse. It then races across the solar system as the “solar wind,” dragging the sun’s magnetic fields along for the ride.

The solar wind underpins the flow of magnetic fields and charged particles throughout the solar system, which is known as “space weather.” Understanding space weather is more than a matter of curiosity; when it grows severe, it can disrupt our technological systems and harm astronauts who are in space during an event. 

The most hazardous space weather happens when large clouds of plasma and magnetic fields called “coronal mass ejections” erupt from the sun, or when jets of highly energized charged particles called “solar energetic particles” accelerate toward Earth, following the sun’s magnetic fields like a kind of cosmic highway. When these solar storms arrive, they can deliver dangerous doses of radiation to astronauts, damage satellites and disrupt power grids on the ground.

If we don’t know the answer to these basic questions, the rest of the field doesn’t have much of a real foundation to stand on.

One of the more disruptive coronal mass ejections in recent years left around 50,000 people without power in Sweden in 2003. The largest recorded storm caused by a coronal mass ejection, called the Carrington Event, occurred in 1859. It damaged telegraph systems and caused visible aurora in skies around the world. A similar event today would likely cause widespread blackouts and lasting damage to the power grid.

Advance warnings of hazardous space weather could help us prepare for and mitigate the damage, but scientists don’t have enough knowledge of the sun to predict a solar eruption before it happens. They can’t identify a hazardous coronal mass ejection until it’s about an hour away from impact on Earth, and the advance warning of a solar energetic particle event can be as little as ten minutes. Even fundamental questions like how the corona’s plasma gets hot enough to accelerate into the solar wind are not fully understood.

“If we don’t know the answer to these questions, the rest of the field doesn’t have much of a real foundation to stand on,” said Mojtaba Akhavan-Tafti, an assistant research scientist of climate and space sciences and engineering at U-M who studies the sun’s magnetic fields and their effects on Earth.

Close encounters with the sun

Michigan Engineering has been a leader in tackling these heliophysics and space weather forecasting challenges for decades. U-M researchers developed the only space weather model used by NOAA’s Space Weather Prediction Center, and they also lead the newly funded CLEAR Center, which NASA will rely on to predict the activity of solar energetic particles between the Earth, Mars and the moon. In addition, U-M researchers have played lead roles in key solar missions, including NASA’s Parker Solar Probe and Solar Orbiter. 

Launched in 2018, Parker Solar Probe has flown into the corona to uncover new information about how its plasma gets so much hotter than the surface of the sun. During Parker’s unprecedented journey, it measured the density and temperature of the corona’s plasma using instruments developed by Justin Kasper, a professor of climate and space sciences and engineering. 

By pairing this data with magnetic field measurements made by other instruments on the probe, scientists have discovered that the sun’s magnetic field has thousands of S-shaped kinks near the corona. The stronger the magnetic field gets in these kinks, the faster the plasma flows. Some scientists think these magnetic zigzags, called “switchbacks,” could be moving magnetic energy to parts of the plasma where it otherwise wouldn’t be, potentially heating the solar wind in the process.

Parker’s measurement capabilities, however, are limited to its immediate vicinity. To get a wider vantage point, NASA and the European Space Agency launched Solar Orbiter on Feb. 9, 2020. The orbiter is positioned further from the sun than Parker, enabling it to photograph larger areas of plasma. Solar Orbiter can also sample the solar wind using a sensor that was developed in part by Susan Lepri, a professor of climate and space sciences and engineering, and Jim Raines, an associate professor of climate and space sciences and engineering. The sensor can detect coronal mass ejections traveling along the solar wind by identifying the heavy particles—like charged iron atoms—that accompany them.

By comparing the location of these heavy particles with photos of coronal mass ejections on the sun, scientists can trace where on the sun the particles likely came from, helping them understand how the storms form. That information is critical when building models to predict solar eruptions in advance.

The orbits of Parker Solar Probe, Solar Orbiter and SunRISE, which appear as white lines around the sun in this infographic, provide each spacecraft with a unique vantage point. The closest to the sun is Parker Solar Probe, which has flown as close as 3.8 million miles from the sun. The cylindrical probe is around three meters long and one meter in diameter. As it flies around the sun, the flat face of its cylinder faces the sun. Parker has instruments for measuring the energetic particles, electric fields, magnetic fields and radio emissions in the solar wind and can take visible-light photographs.

The data collected by Parker and Solar Orbiter has enabled scientists to get a closer look at the sun than ever before, and the new CLEAR Center is combining the information gathered by these and other space missions into a benchmark public dataset for creating 24-hour forecasts of solar energetic particle storms.

“Because Parker Solar Probe and Solar Orbiter are viewing the sun in ways most space instruments haven’t, they are collecting data where we haven’t had much information before,” said Lulu Zhao, an assistant research scientist of climate and space sciences and engineering and the principle investigator of the CLEAR Center.

“That can help us know whether our forecasting models are accurate for locations in the middle of the solar system, which builds confidence in our ability to forecast when solar energetic particles might hit space missions at the moon and Mars,” Zhao said.

Studying the sun from Earth

While missions like Parker and Solar Orbiter study the sun from space, the eclipse offers the opportunity for a different perspective that could uncover new data about the sun’s inner workings and how it shapes the rest of the solar system, including the Earth.

One of the efforts that’s turning to the eclipse for clues about the sun is called Coronacast. Composed of five U-M graduate students in climate and space sciences and engineering and two graduate students from the University of Texas at Arlington, the Coronacast team aims to complement Parker’s work and help build a better understanding of how plasma and magnetic fields behave inside the sun. 

They’ve helped develop a computer model that predicts the corona’s shape and size based on theories of how the corona is heated and how its magnetic fields fluctuate. The eclipse offers the team a rare opportunity to compare their model to real-world observations. On April 8, they’ll gather at the University of Texas at Arlington to make those comparisons with the help of three photographers from the International Astronomical Union.

“We’ll be comparing the real-world and model images live on YouTube and social media during the eclipse, so we’ll show our pictures and think: ’How well did we do?’ But we can also get a lot of science from that,” said Daniel Welling, a U-M assistant professor of climate and space sciences and engineering who is helping to organize Coronacast.

Follow the Coronacast team live on April 8, 2024.

“Right now, we don’t know how to turn the dials on most of the parameters in our models that describe how plasma in the corona behaves, and the eclipse could help us learn where to set those dials. The more we understand the real system, the more we can include real-world processes in our space weather forecasting tools.”

Once the eclipse begins, the Coronacast team will download images of the corona’s magnetic fields from several space weather satellites that observe the sun from Earth’s orbit. Meanwhile, photographers from the International Astronomical Union will deploy their telescopes and cameras nearby to photograph the corona as it comes into view.

Right now, we don’t know how to turn the dials on most of the parameters in our models that describe how plasma in the corona behaves, and the eclipse could help us learn where to set those dials. The more we understand the real system, the more we can include real-world processes in our space weather forecasting tools.

The Coronacast team also includes scientists and engineers with the Center for Astrophysics Harvard & Smithsonian and crew members from the National Center for Atmospheric Research (NCAR). Their eclipse mission will start further south, in Tucson, Ariz. There, the crew will take off in the National Science Foundation’s Gulfstream V airplane for a close look at the corona. After lifting off, the team will fly into the path of the eclipse, enabling their Airborne Coronal Emission Surveyor (ACES) to measure the corona’s infrared light as the plane flies through the shadow of the moon between Austin and Dallas, Texas.

Studying that infrared light will help scientists better understand how the chemical composition, temperature and density of the plasma changes throughout the corona and with fluctuations in its magnetic field. Each type of particle in the corona’s plasma absorbs and emits characteristic frequencies of infrared light, and the amount of light emitted at each frequency depends on the plasma’s temperature and density as well as its magnetic field activity. The ACES measurements will help the Coronacast modeling team determine the physics that govern the flow of heat and energy throughout the corona. The Center for Astrophysics team also stands to gain from the measurements, which will enable them to determine which infrared wavelengths could be most promising for monitoring the corona’s magnetic field from Earth.

The team’s aerial vantage point offers two big advantages over monitoring the corona from the ground. First, the plane’s speed enables the team to keep up with the eclipse’s movement across Texas, extending the time they can gather useful data by nearly 50 percent. In addition, the plane’s altitude gives the team better access to infrared wavelengths that would be absorbed by the Earth’s atmosphere if measured from the ground.

The best data will come from the brightest features in the corona—the long streams of plasma that appear as dazzling rays of light to ground-based observers. To measure the plasma in those streams, the ACES team needs to carefully position their instruments aboard the plane so they can lock onto those regions of the corona, and there’s no way to adjust the instrument mid-flight. Luckily, they’ll have the Coronacast team’s models to help get the instrument into the best orientation before the plane takes off.

“The sun takes around a month to completely rotate, so predicting structures in the solar atmosphere can provide a good indication of what the corona will look like. However, a lot can change in a month,” said Yeimy Rivera (PhD CLaSP ’20), who is now an astrophysicist at the Center for Astrophysics and the ACES project scientist.

“The Coronacast team’s predictions are extremely valuable because they give us a better idea of what the corona will look like come eclipse time,” Rivera said. “The models will be good at predicting the coronal structure in advance based on the sun’s current configuration and will also help predict new structures that could appear across the month.”

The relationship between the three teams is symbiotic; while the ACES team can use Coronacast’s models to better position its instrument, the Coronacast team can use the ACES team’s data to make future models even better. After the eclipse, the Coronacast researchers will compare the new collection of data and images to those generated by their computer models. If the team finds a close match, they will know their theories are on the right track and could perhaps lead to future tools that can more accurately predict space weather, according to Welling.

Data from Parker Solar Probe will also play a role on the day of the eclipse. In March 2024, it dove into the corona for the 12th time, flying through a region that will be clearly visible from the ground during the eclipse. Parker’s flight path could give ground observers a chance to compare the probe’s direct measurements of the corona’s plasma and magnetic field to the light viewers see on Earth.

Listening for answers

While the Coronacast team gathers visual and infrared information, high school students all over the country will be searching for a different kind of data: radio waves emitted by the sun at the long end of the electromagnetic spectrum. By tuning in to the sun’s radio signals, the students will be helping scientists better understand coronal mass ejections and solar energetic particles.

Today, it’s impossible to predict coronal mass ejections before they’re detected on the sun. But scientists have noticed bursts of radio energy that occur before both coronal mass ejections and eruptions of solar energetic particles. They believe that a better understanding of those radio bursts could one day help us predict severe space weather before it happens.

Capturing those radio bursts is a goal of the Sun Radio Interferometer Space Experiment, or SunRISE. The mission, which is led by Kasper and managed by NASA’s Jet Propulsion Laboratory, will launch an array of six toaster-size CubeSats into orbit around Earth. The CubeSats will form a radio dish that will be able to triangulate where exactly radio signals on the sun or within a coronal mass ejection come from. 

SunRISE will give a new look at the sun by detecting low-frequency radio waves produced inside the corona. Such waves can’t be detected from Earth because they are absorbed by our atmosphere.

“We want SunRISE to image which part of these eruptions are making those radio bursts so we can understand why the storms make those radio bursts and how they line up with Earth,” Kasper said.

The space mission will be supported by a ground-based component of the experiment, called the SunRISE Ground Radio Lab, which is led by Akhavan-Tafti.

Starting in June 2023, Ground Radio Lab provided students at 17 high schools across the United States with radio antennas. The students installed them on their school roofs and have been learning how to operate them ever since. They’ll use them to capture any radio bursts that occur during the eclipse, when the moon will block out most of the sun’s radio chatter and make the bursts easier to detect.

The data the students gather during and ahead of the eclipse will complement SunRISE’s space-based data by enabling researchers to compare similar signals gathered from different vantage points. Differences between the ground and space measurements can also be used to determine how space weather changes the properties of the uppermost layer of Earth’s atmosphere, called the ionosphere. If a solar storm disrupts the ionosphere too much, it can potentially distort GPS and other communication signals, sending the people and technology that rely on them off course.

Our goal is to expose students of all backgrounds to space sciences and engineering early in their careers, with the hope of inspiring tomorrow’s space scientists, engineers, entrepreneurs and decision makers.

In addition to the scientific data gleaned by the SunRISE Ground Radio Lab, the project is giving high school students around the country their first opportunity to participate in scientific research and master the assembly and operation of scientific equipment. Akhavan-Tafti believes that experiences like these are just as important as the radio data they hope to gather.

“Our goal is to expose students of all backgrounds to space sciences and engineering early in their careers, with the hope of inspiring tomorrow’s space scientists, engineers, entrepreneurs and decision makers,” Akhavan-Tafti said. 

If the experience of the students at Hamtramck High School is any indication, Akhavan-Tafti’s plan appears to be working. The students formed a new astronomy club specifically to contribute to the SunRISE ground radio lab. Madeha Rahman, the head of the club, organized the efforts to get her school’s antenna running and even convinced her parents to set up a second antenna at their house. Once they saw the chance to get hands-on, fellow students Aymen Saleh and Mohammed Miah also joined the club. Since then, their interest in physics and chemistry has skyrocketed.

“It’s the first time that I’ve seen them enjoy a long-term project,” said Natalia Olar, a chemistry teacher at Hamtramck Senior High School. “My students are the greatest thing in the world to me, so seeing them get involved and learning and being curious about the world beyond what we see has been the most rewarding part of the project.”

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