NASA’s solar probe delves into burning questions about the sun
More than a year after NASA launched a small probe into the sun’s atmosphere, the spacecraft has sent back its first set of data, both answering and raising questions about the behavior and environment of the fiery star around which the Earth orbits.
The initial returns provide fresh detail on the source of solar winds and solar energetic particles — findings that will help scientists predict dangerous, high-radiation space weather that could damage satellites and other loworbit technology as well as harm astronauts in space, given the constant human presence at the International Space Station.
More broadly, the information will be instructive for scientists in reshaping how they model the sun’s activity and may help them better understand the life cycle of other stars and how planets are formed.
“This is the first time we’ve ever been able to fly a spacecraft into the atmosphere of a star, and that alone to me is just so exciting,” said Nicola Fox, director of the NASA division that studies the sun and atmospheres of planets. “It’s our nearest star and it has a profound effect on our Earth, but we’ve waited for decades and decades to understand these mysteries.”
The $1.5 billion Parker Solar Probe was launched in April 2018 as part of a seven-year mission to shed light on how and when the star’s solar winds accelerate to supersonic speeds, and why the sun’s corona — its atmosphere — has such a high temperature, among other burning questions. At its closest approach, the spacecraft travels at approximately 430,000 mph and within 3.8 million miles of the sun, where the highest-energy solar particles are born.
The probe, about the size of a small car, traveled into the corona. The orbit path includes flying by Venus, where the planet’s gravity acts like a slingshot and sends the craft closer to the sun, and withstanding temperatures of nearly 2,500 degrees Fahrenheit to transmit data about Earth’s star back to scientists on the ground. Its instruments study the sun’s magnetic fields, plasma and energetic particles. The probe has completed three of 24 planned orbits so far.
A 4.5-inch thick, 8-foot diameter carbon shield protects the probe (and the instruments inside it) from the heat and energy of the corona. This shielding guards the probe from temperatures of upwards of 3,000 degrees Fahrenheit. The spacecraft on the other side of the shield remains at a balmy 85 degrees Fahrenheit, according to NASA.
The discoveries from the first tranche of data from the probe will lead to a complete readjustment of how scientists model the sun, Fox said.
Scientists had long known that space is full of cosmic dust, visible from Earth because it reflects sunlight. The Parker probe saw evidence that the dust stops at an estimated 3.5 million miles from the sun. As the dust gets closer to the sun, it vaporizes, creating a dust-free zone around the star.
Solar wind has also been the subject of intense scrutiny since 1958, when scientist Eugene Parker, for whom the space probe is named, hypothesized its existence.
Parker, 92, was shown reacting to the initial findings of the solar probe in a video released Wednesday by NASA. His eyes welled as he reflected on the probe’s journey.
“All I can say is, ‘Wow,’” Parker said. “As usual, when you have a space mission into an unknown place, you find remarkable things that you did not anticipate.”
Scientists have wondered if the solar wind is generated as a continuous flow or in spurts. Imaging from the space probe shows evidence that the solar winds are quite turbulent, with plasma and clumps of solar material firing out into space while others fall back into the sun.
Stuart Bale, a physicist at University of California, Berkeley and principal investigator of the instruments on the probe that measure magnetic and electric fields, compared the solar winds to a waterfall of unknown origin.
“What Parker has done is gotten us closer than ever to the sun so now we can really see a lot of the structure and the source of the wind too,” Bale said.
At the probe’s closest approach to the sun, it measured slow, highly magnetized solar winds coming from a small “coronal hole” at the sun’s equator, at lower altitudes than scientists expected. Coronal holes are regions of cool gas with magnetic fields that thread out into planetary space and that are associated with sunspots.
These clumps of material could be distorting the sun’s magnetic field, causing “switchbacks” — magnetic field lines that flip in a whip-like motion, turning 180 degrees in a matter of seconds. These switchbacks came in clusters and were timed with fast-moving clumps of plasma in the solar wind.
The exact source of the switchbacks is unclear, but the probe’s measurements have allowed scientists to narrow down the possibility that it might be a kink in the sun’s magnetic field. The probe’s next mission, on Jan. 29, will carry the spacecraft nearer to the sun than ever before, and may shed new light on this process.
The probe was also able to narrow down the point of where the solar winds flowing from the sun transition from a rotational flow to a straight flow, as seen from Earth. This has implications for how the sun sheds energy, and finding that transition point may help scientists better understand the life cycle of other stars and how planets are formed.
Perhaps most importantly, considering the constant and future presence of humans in low-Earth orbit at the International Space Station, the probe observed tiny bursts of solar particles that spread out as they move from the sun, making them undetectable from Earth. These particles contain dangerous levels of radiation, a potential threat to satellites and astronauts in space.
The solar particles could also be telling in how the sun’s corona generates heat. Solar physicists like Stephen Bradshaw at Rice University have theorized that the sun’s heat may be derived from a series of small-scale “events” or bursts of energy, and these previously unseen solar particles may be evidence of that.
“What is intriguing to me, these new low-energy distribution of particles that the probe seems to have measured is some initial tantalizing evidence for perhaps these kinds of events,” Bradshaw said.
The Parker probe will eventually travel to about 3.83 million miles from the Sun’s surface, more than three times closer than these recent encounters, in 2024.