As Earth enjoys an eclipse, a NASA probe prepares to ‘touch the sun’

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The sun is having a glamorous year. It’s in solar maximum, the peak of its 11-year storm cycle. It has been hurling large masses of charged particles at Earth on a regular basis, intensifying high-latitude auroras. And in a particularly extravagant star turn, the sun will hide behind the moon on April 8, offering tens of millions of people in North America the chance to experience a Total solar eclipse.

Overshadowed by all this is a risky NASA mission that is about to send a spacecraft hurtling almost within striking distance of the sun.

The Parker Solar Probe launched in 2018, is designed to “touch the sun,” as NASA says. On December 24, the probe will make its closest pass, approaching within 3.8 million miles of the surface, having been accelerated by gravity to more than 430,000 miles per hour.

No spacecraft has ever flown so fast or so close to the sun.

“It’s a journey into the unknown,” said NASA’s chief science administrator, Nicola “Nicky” Fox, who tells everyone that “it’s the coldest and hottest mission under the sun.”

At a cost of $1.4 billion, this mission is not cheap. That NASA has invested so much money and effort is a reminder that the sun, which is so basic to our survival, is not fully understood.

“We live in the atmosphere of the sun. “Everything that happens on the Sun, we feel the effect here on Earth,” Fox said. “If the sun sneezes, the Earth catches a cold.”

There is also a more subtle agenda to this mission: promoting American aerospace prowess. Technological innovations can be applied to future space projects at a time when many countries are sending probes to the Moon, Mars and other parts of the solar system.

“The question is whether we stay on top of the world or someone else will intervene,” said Nour Raouafi, the mission’s project scientist and astrophysicist at the Johns Hopkins University Applied Physics Laboratory in Maryland.

His eyes light up as he describes the amazing feat of this spacecraft: “We will almost be landing on the star.”

How to survive a visit to the sun

Fun fact: you can’t land in the sun. In reality, there is no distinct surface. When scientists talk about sunlight surface, refer to the “photosphere”, the lowest visible layer of the atmosphere.

At its closest approach on Christmas Eve, the Parker probe will be seven times closer to the Sun than any other spacecraft it has ever ventured to. NASA engineers hope the public understands that getting so close to the sun is not a day at the beach.

“This is a high-risk mission. When you enter the atmosphere of a star, it’s really tough,” Raouafi said.

The probe is adorned with instruments that take measurements of the solar wind, including temperature, density and speed. The solar wind reaches the outermost edge of the solar system. The Earth is completely immersed in it, but thanks to our planet’s magnetic field, we are normally protected from the most harmful solar radiation.

“We ourselves live in that environment. But we don’t feel it because we have a geomagnetic field that protects us from these dangerous energetic particles and these explosions from the sun,” Raouafi said. “That’s why we have life on Earth.”

The solar wind is also protective because it limits the impact of cosmic rays, particles that move at tremendous speed and come toward us from all directions in our galaxy.

What all this illustrates is that space has a climate. A highly technological civilization needs to pay attention to space weather, because an explosion of solar material called A coronal mass ejection aimed directly at Earth could generate a debilitating geomagnetic storm.

NASA and other governments The agencies are especially concerned about a repeat of what is known as the Carrington event. In 1859, a coronal mass ejection hit the Earth and caused the telegraph lines to sing. A similar storm today could cause radio or satellite outages or even, in the worst case, render the electrical grid unusable.

That’s why engineers at Hopkins Laboratory and NASA want to get closer to the sun and really understand its volatile atmosphere. But first, they had to figure out how to prevent the Parker probe from being cooked, toasted, immolated, or otherwise destroyed by coronal mass ejections and the solar wind.

Two pieces of technology are particularly crucial to the success of the mission. The most obvious is the heat shield. You don’t fly near the sun without a good heat shield.

The shield is coated with an ultra-white plasma spray to reflect as much solar radiation as possible. The surface is perfectly uniform to avoid hot spots and cold spots. The shield has a carbon foam interior, sandwiched between layers of a carbon composite similar to what can be found in a golf club or tennis racket.

This 4.5-inch thick heat shield allows the sun-facing side reach 2,500 degrees even when the body of the spacecraft is at a comfortable 89 degrees, according to NASA.

And there is another reason why the spacecraft does not turn into molten substance: although the temperature of the sun’s atmosphere can reach millions of degrees, the density is low, so an object flying through that realm of space it will not get hot easily.

However, this shield will only work if you are always directly facing the sun, with the vulnerable hardware behind completely shadowed. That requires precise navigation with multiple cameras that use the “fixed” stars as guides.

Solar panels are ingenious. Flying close to the sun and then very far away is a recipe for power surges. The panels can then bend like bird wings and hide.

Mission scientists also had to overcome a major obstacle: the inflexible laws of gravity.

“Believe it or not, it’s extremely difficult to get anything close to the sun,” Raouafi said.

This is because a spacecraft launched from Earth carries with it the angular momentum of our home planet as it orbits the sun. Pointing a spacecraft directly toward the sun would require an unrealistic amount of fuel. One possible solution would be to send the spacecraft to Jupiter, which would launch it back to the sun. But that would take many years.

NASA ultimately opted for a strategy that uses multiple close passes. of Venus, each time losing some of the spacecraft’s orbital momentum, allowing it to get closer to the sun with each orbit.

The most tense moment of the mission

The Parker spacecraft has made 18 trips around the sun and, in late December, passed just 4.51 million miles from the surface, emerging from that scorching trip in top shape.

The probe has already collected extensive data about the solar corona, the ethereal outermost layer of the sun that is normally invisible to human eyes. The total eclipse on April 8 will offer Earth’s inhabitants a rare opportunity to glimpse the corona when the Moon completely blocks the main disk of our fiery star.

NASA can precisely map the path of the Moon’s shadow and the timing of its totality at each location on April 8. However, to a heliophysicist, the big star in the sky is not as predictable as it seems. Among the things scientists don’t fully understand about the sun is what they call the “coronal heating problem.”

The crown is about 300 times hotter than the surface of the sun. This is contrary to common sense. When you walk away from a campfire on a cold night, the air doesn’t get warm, but that’s how it is near the sun.

Scientists have been trying to solve the problem of coronal heating for decades. Data from the Parker probe, along with observations during eclipses by heliophysicists on Earth, could put an end to this mystery of sunlight.

The most tense moments of the mission are when the spacecraft is orbiting the sun and temporarily unable to receive orders. That will happen next December during the closest encounter: For days, the team won’t know if the spacecraft survived.

“That spaceship becomes part of your team,” Fox said. She should know; Before coming to NASA, she worked at the Applied Physics Laboratory and was the principal scientist on the Parker probe mission.

The probe is named after pioneering astrophysicist Eugene Parker. As a young scientist at the University of Chicago, Parker proposed the existence of the solar wind in the 1950s. His idea was initially dismissed and ridiculed by many scientists, but was confirmed by later space missions.

Parker himself attended the launch of the probe in 2018. According to NASA, he was the first person to witness the launch of a spacecraft that bears his name.

He died in 2022 at the age of 94.

Parker was amazed and excited, Fox said, when he first saw the spacecraft in the Applied Physics Laboratory’s clean room before launch.

Then, as he watched the probe take to the skies to begin its historic journey, Parker felt melancholy, Fox recalled.

“It’s very sad,” he told her. “It will never come back”.

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