NASA’s Parker Solar Probe is crashing through a hailstorm of dust as it hurtles towards the sun at awe-inspiring speed.
The probe’s team members found that high-speed impacts with dust particles are not only more common than expected, they’re making tiny plumes of superhot plasma on the surface of the craft, according to an announcement for a new study.
The probe’s main mission goals are to measure the electric and magnetic fields near the sun and learn more about the solar wind—the stream of particles coming off of the sun, says David Malaspina, a space plasma physicist at the University of Colorado Boulder Astrophysical and Planetary Sciences Department and Laboratory for Atmospheric and Space Physics. Malaspina led the study, which the team will present at a conference this week.
Scientists have studied the solar wind from a distance, Malaspina says, but “there’s a lot of fundamental questions about how the solar wind is born…that we really can’t answer using measurements only close to Earth.”
The probe is the fastest human-made object, currently traveling at over 100,000 miles per hour through the zodiacal dust cloud—the huge cloud of “the leftovers from asteroids and comets throughout the solar system” that are slowly falling toward the sun, Malaspina says.
The Parker Solar Probe wasn’t made to study dust. But, to get close to the sun and study the solar wind, it “plows right through the densest part of the zodiacal cloud,” Malaspina says. It can get a rough estimate of the dust’s density by tracking dust collisions. And with each orbit, the spacecraft gets closer to the sun and speeds up. “Imagine driving into a sandstorm but doing it faster each time,” he says.
The mission team expected the probe would encounter dust, but without local measurements to rely on, they didn’t expect quite this much of it. On the previous orbit, the probe’s ninth pass around the sun, it got hit every twelve seconds on average, Malaspina says. If you could stand next to the spacecraft, you would see the holes in the spacecraft’s mylar protective coating, called a Whipple shield, he says. But so far, the shield has “held up against all impacts.”
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Malaspina says the team is most worried about the cooling system, because the sun-facing part of the spacecraft can reach almost 2000°C. Water pipes run behind the heat shield and transfer the heat to radiators that dissipate it into space. Puncture one of those pipes and the spacecraft would definitely burn up, he says.
Building a craft that can survive this harsh environment “all comes down to choosing the right materials that you know are going to survive these impacts, and doing a lot of tests and analysis ahead of time,” says Jim Kinnison of the Johns Hopkins Applied Physics Lab, who is the mission system engineer for the Parker Probe. These tests include a hypervelocity impact chamber, Kinnison says, which can recreate space dust encounters by launching tiny, incredibly high-speed particles at materials here on Earth.
Although the dust grains near the sun seem to be more plentiful, they’re less massive than expected—luckily for the Parker Solar Probe—so the risk of serious damage to the spacecraft is still low, Malaspina says.
Despite their lightness, when dust particles hit the spacecraft with so much energy, Malaspina says, “they not only vaporize themselves, and a fraction of the spacecraft surface, but they also ionize it,” meaning they tear the electrons off their nuclei and create a tiny, short lived plasma blast with each impact.
Plasma has a strong electric charge, so these little spurts cause a spike in the electric field around the craft, which the spacecraft can measure.
Spacecraft have picked up these spikes before, but the plasma clouds around the probe are more intense than expected, Malaspina says. They are so dense that they noticeably interact with the solar wind, in a process that resembles the way the solar wind interacts with Venus, Mars, and other planets that lack a magnetic field. On those planets, sunlight ionizes part of the atmosphere, allowing the solar wind to sweep some of it away.
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The probe is continuing to move closer to the sun, into a region where scientists have long predicted that the intense solar heat has burned up all the dust. In fact, it’s possible the probe’s imaging team may have already observed this for the first time. Over the next few orbits, the spacecraft will get close enough to verify that finding with direct electric field measurements.
Despite these extreme conditions, the spacecraft is likely to survive until its planned destruction. Eventually, it will get so close to the sun that the probe will burn up and become part of the solar wind itself, which, Malaspina says, is “sort of a poetic ending.”
