There are some places in the solar system that humans will never go. The surface of Venus, with its thick atmosphere and crushing pressure, is inaccessible. Outer worlds, such as Pluto, are currently too far away for any kind of robotic exploration. And the sun, our burning bright ball of hydrogen and helium, is too hot and messy for the astronauts to get up close. In our place, an intrepid robotic explorer, the Parker Solar Probe, has been making a series dramatic leaps towards our stargetting closer than any spaceship to unlock its secrets. Now it is about to make its final closest passes, passing through the solar atmosphere like never before.
“It’s a big moment,” says Yanping Guo, a space mission designer at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) in Maryland. “Throughout 60 years of space exploration, the sun has been the most difficult destination to reach.”
On Christmas Eve, December 24, Parker will fly just 6.1 million kilometers from the sun’s surface, or 9.86 solar radii from the sun’s center, ten times closer than Mercury orbits the star and the first of three very close flybys. It will do so at an astonishing 690,000 km per hour, faster than any spacecraft in history (though still only 0.064 percent of the speed of light). While flying, Parker will move fast enough to travel from London to Paris in less than two seconds; its speed will be so great that relativistic effects such as time dilation and drag frame can be recorded on spacecraft instruments.
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The spacecraft will fly through the sun’s atmosphere, its crown, where some the biggest questions about our star remain, including why the corona is much hotter than the solar surface and how the solar wind accelerates. While other spacecraft have studied the sun, only Parker has come this close. “There is no precedent,” says Thomas Zurbuchen, former associate administrator of NASA’s Science Mission Directorate. “It’s really an exploratory mission.”
It was Zurbuchen who later named the spaceship The late US solar physicist Eugene Parkerwho predicted the existence of the solar wind in the 1950s. The mission It was launched in 2018the culmination of decades of studying how to do it “touch” the sun.. Getting close to our star is surprisingly difficult because you have to “kill Earth’s orbital speed” to fall toward it, says Ralph McNutt, chief scientist of JHUAPL’s space department. Scientists have long thought the best way to do this was to fly to Jupiter, then use the gas giant’s gravitational pull to plunge toward the sun. That mission would get you very close, only four solar radii away, but at the cost of being very difficult and time-consuming, it might only give you one or two close passes of the sun, with an orbital period of nearly five years.
In 2007 Guo proposed instead Multiple planes of Venus It could be used to bring a spacecraft into similar proximity but a little further, but adding the benefit of dozens of passes over several years with an orbital period of just three months. “The requirement was to be close enough to take samples inside the solar corona,” says Guo. “I found you can use seven Venus flights.” The last of these flybys took place on November 6, when the spacecraft descended 387 km from the surface of Venus. Since then, in the last six years, he has been on a course that will take him closer than any of the previous 21 passes; its last solar flyby in September was about a million km, or 10.4 solar radii, further away.
Parker carries four instruments to study the sun. This includes a camera to image our star and its surroundings, an instrument to measure electric and magnetic fields, and two more to study solar particles and plasma showering the spacecraft. Throughout the mission so far, Parker has done helped discover it Magnetic fields on the Sun’s surface can transport heat into the corona and found more particles from the Sun than expected. These results are due to the fact that Parker crossed and crossed the sun’s corona, which happened for the first time in April 2021.
These latter jets will take the spacecraft deeper into the corona, although there is a missing supersonic threshold around four solar radii, where the solar wind is thought to reach the speed of sound. Even from Parker’s view, which is about 10 solar radii away, scientists hope to learn more about the solar wind, exactly what makes it different between “fast” (up to 800 km per second) and “slow” (up to 300 km). per second) varieties. “We think the fast wind comes from the hole crowns, and the slow wind may come from the edges of those holes,” says Steph Yardley, a solar scientist at Northumbria University in England. “But it’s something we’re still discussing.” This process can also tell us how more space weather The solar wind is created on Earth as it flows towards our planet. “The closer we get to the source region of the particles that create space weather, the more we learn,” says Joseph Westlake, director of the heliophysics division of the Science Mission Directorate at NASA Headquarters in Washington, DC.
There is also hope that Parker will fly past the sun in an eruption. The sun is called right now maximum suna time of high tumult the 11-year activity cycle of our star. This increases the chances of randomly timed eruptions showering the spacecraft, at least something that has happened. a previous one. “We hope to collect more of these events very close to the Sun,” says Parker astrophysicist and project scientist Nour Rawafi at JHUAPL, “because we need to understand how events like flares and coronal mass ejections accelerate particles to relativistic speeds.” It may also find a zone, a hypothesized region close to the sun, where debris moving inward from the solar system “evaporates,” he says. John Wirzburger, Parker systems engineer at JHUAPL.
The action this time will begin on December 20, when the spacecraft reaches 0.25 times the Earth-Sun distance, 37 million km or 53 solar radii from the sun. Here, ready to dive, the spacecraft will send a short beacon tone to Earth, confirming its good health. To survive the close pass and the intense conditions that follow, Parker must hide most of its hardware behind a carbon composite heat shield. This heat shield is so effective that, despite temperatures reaching around 1,000 degrees Celsius, the spacecraft’s instruments remain “essentially at room temperature,” says Wirzburger.
The location of the spacecraft and heat shield and the desire to maximize data returns means that the spacecraft cannot communicate with Earth during this pass. It flies completely autonomously, changing its position slightly to follow the movement of the sun, keeping its heat shield precisely pointed in the direction of the stars to create a cone-shaped shadow that completely encloses its precious instruments. The only other part of Parker that will see the sun during the flight will be a small patch of solar panels embedded in the sides of the spacecraft to generate power from our star’s immense brightness.
The full encounter with the sun will last about a week, with the spacecraft reaching its closest point around 6:40 a.m. on Christmas Eve. If you were to survive here and avoid instant blindness from the sun’s immense light—500 times more intense than seen from Earth—our star would appear to you as a massive disk 22 times larger than the full moon in our planet’s sky. “It would fill up a lot of space in front of you,” says Rawafi. Parker’s camera, pointed sideways, will see the trails of particles moving through the surrounding corona, while its other instruments collect their vital data. But what specifically they’ll see if anyone can figure it out. “We don’t really know,” Zurbuchen says.
The team won’t know if the flight was successful until Dec. 27, when the spacecraft reaches 35 solar radii on return and emits another beacon tone to announce its survival. The team will then prepare to collect invaluable data from the spacecraft beginning on New Year’s Day, and return in the coming weeks and months. In March, Parker will do it all again when he flies next to the sun, before another final closed passage in June. The gravitational pull of distant Jupiter will technically make these two later spacecraft a little closer to the sun—each about 100 km closer, a mere rounding error in the billions of miles between Parker and our star. Practically speaking, the Christmas Eve flight will be as close to the sun as Parker will ever get.
The consequences of these close encounters will also end the main mission of the spacecraft, but may be extended later. Parker, for example, could be left in its current orbit to monitor the effects of the lower solar maximum. “It would be surprising to see this decline,” says Westlake, because many large solar events are predicted to occur during this period. The spacecraft could begin moving into a more inclined orbit with remaining fuel, moving out of the ecliptic plane in which most planets rotate, to get a slightly different view of the sun and toward its polar regions, despite the high cost of flying. a little further “We want to be very close to the sun,” says Rawafi.
Whatever the mission, the data Parker collects will be analyzed for years. “This is the closest humans have ever come to a star,” says Westlake, a record likely to be unbeaten in the future.
