The fastest object ever created by humans has discovered intensely energetic rogue waves within our Sun, and detected solar wind speeds beyond what any model had predicted. Neither discovery was expected, or can be easily explained, suggesting that there are significant gaps in our understanding of the Sun.
NASA’s Parker Solar Probe, launched in 2018, traveled closer to the Sun than any previous mission for several days last November and in April 2019. Scientists revealed the incredible findings from these first two close encounters from the swiftest spacecraft ever in a batch of four papers published in Nature on Wednesday.
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Though the Sun is the center of the solar system and its radiation has nurtured life on Earth, it is one of the most unexplored objects in space because of its intense heat and radiation.
“It’s been very exciting,” said Justin Kasper, lead author of one of the studies and professor of space sciences at the University of Michigan, in a call. “It’s exploration at the cutting edge.”
During its two encounters, Parker traveled within 15 million miles of the Sun’s surface, far surpassing the 25-million-mile record first set by NASA’s Helios 2 mission in 1976. Parker has also claimed the title of the fastest human-made object in history from Helios 2, as it surfed near the Sun at over 153,000 miles per hour.
In a surprising discovery, Parker detected new phenomena within a quarter of an astronomical unit (AU), the distance between Earth and the Sun, of the solar surface. At that distance, the probe reported that the solar wind, which is a stream of charged particles emitted by the Sun, was rotating around the star at speeds far beyond what models had estimated.
“To our big surprise,” Kasper said, “by the time we got to our closest approach, [the solar wind] was flowing between 35 and 50 kilometers per second around the Sun. That’s something like 15 to 25 times faster than the standard solar models predict, so we’re missing something really fundamental in our standard models of the Sun—how it rotates and how the wind escapes—and that’s really interesting.”
Parker was also pummeled by a series of extraordinarily intense “Alfven waves” in the solar wind. Interplanetary missions have long observed less energetic Alfven waves, which are ripples that flow through magnetized plasma from the Sun. But Parker is the first to brace the “giant rogue waves” near our star.
“Every now and then, suddenly within seconds, the speed of the wind would jump by about 300,000 miles an hour,” Kasper explained. “Then, for seconds or hundreds of seconds, the spacecraft would sit there washed by this spike in the speed of the wind, and then just as quickly it goes away.”
These spikes are so violent that they distort and twist the magnetic field as they pass through it. “It gives you a sense of just how much energy is in these rogue waves as they go by compared to the regular Alfven waves that we’ve seen before,” Kasper said.
Though the mechanism behind these waves is still unknown, the sheer force of them may help explain two of the most persistent mysteries about the Sun: Why is solar corona, or the atmosphere of the Sun, about 1,000 times hotter than its surface? And why does the solar wind suddenly accelerate to supersonic speeds at a certain distance from the Sun?
Scientists suspect that an enigmatic process dumps heat and energy into the solar corona. The newly detected rogue waves might be a part of this dynamic.
“We were looking for buckets of energy when we got closer to the Sun, and we’re seeing some very large buckets going by, so that’s good,” Kasper said. “In our initial analyses, they’re definitely carrying a lot of energy so they are very promising as an energy source.”
“I’m not going to claim in any way that we’ve solved the mystery but we’ve had some very surprising results to paint the path to closing this question,” he added.
Parker’s new data challenges long-held assumptions about the Sun, which will lead to better models of solar storms that can affect Earth, as well as star evolution across the universe. Plus, the mission is only getting started.
“We’re running out of unexplored territory now,” Kasper said.
