The sun is the most powerful source of energy in the solar system, and the solar winds that escape its gravity affect just about everybody they can reach Solar winds on Earth. On and around Earth, solar winds interfere with satellites, create auroras, and power solar sails in orbit. But there’s still a lot we don’t know about them, like how these winds escape the sun’s crushing gravity or how we can predict them with greater accuracy.
Now a team at University of Wisconsin–Madison is hoping to clear up some of these lingering mysteries surrounding solar wind by building what they call the “Big Red Ball,” a device that can actually mimic solar winds. The Big Red Ball is almost 10 feet wide and is a hollow sphere with a powerful magnet at its center. Scientists pump helium gas inside the Ball and then ionize it, stripping away electrons to create plasma, before finally adding an electrical current. Together, the plasma, the current, and the magnetic field recreate the spinning plasma and electromagnetic fields of the sun.
With the Big Red Ball acting as a mini-sun, they can create their own miniature solar winds. “The solar wind is highly variable, but there are essentially two types: fast and slow,” explains Ethan Peterson, a graduate student in the department of physics at UW–Madison and lead author of the study published online July 29 in Nature Physics, in a press statement. “Satellite missions have documented pretty well where the fast wind comes from, so we were trying to study specifically how the slow solar wind is generated and how it evolves as it travels toward Earth.”
The Big Red Ball allows science to recreate what’s known as the Parker Spiral, named after the famed solar astrophysicist Eugene Parker who theorized the solar phenomenon. These are the naturally occurring Archimedean spiral that the sun’s magnetic field creates as the star rotates. The sun is so powerful that the Parker Spiral touches the entire solar system. These magnetic fields come directly out of the sun, but are twisted by solar winds into a spiral.
“Satellite measurements are pretty consistent with the Parker Spiral model, but only at one point at a time, so you’d never be able to make a simultaneous, large-scale map of it like we can in the lab.” Peterson says. “Our experimental measurements confirm Parker’s theory of how it is created by these plasma flows.” The UW-Madison team also looked at the sun’s plasma “burps,” which NASA scientists have described as “blobs in a lava lamp” but on a cosmic scale. The sun’s burps are hundreds of times the size of the Earth. With the Big Red Ball, scientists located a region in their model where plasma was moving fast enough and magnetic fields were weak enough to escape.
“These ejections are observed by satellites, but no one knows what drives them,” Peterson says. “We ended up seeing very similar burps in our experiment, and identified how they develop.” The UW-Madison team says that while the Big Red Ball is a useful tool, it’s not a replica for the type of research gained from satellites like the Parker Space Probe(also named after Eugene Parker), which has gotten closer to the sun than any previous man-made object.
However, the Parker Space Probe is a costly and time-consuming endeavor, so projects like the Big Red Sun could be supplemental for those without NASA’s budget. “Our work shows that laboratory experiments can also get at the fundamental physics of these processes,” Peterson says. “And because the Big Red Ball is now funded as a National User Facility, it says to the science community: If you want to study the physics of solar wind, you can do that here.”