It's always sunny for heliophysicists, but especially so now.
The Solar Orbiter spacecraft, a collaboration between the European Space Agency and NASA, launched yesterday (Feb. 9), less than two weeks after the first public image from a massive new solar telescope showed off the structure of our star in more detail than humans have ever seen. On that same day, Jan. 29, NASA's Parker Solar Probe made its closest swing pass the sun to date — a record it will continue to break until 2025.
"It's a great time to be a heliophysicist; we're launching lots of new missions," Nicky Fox, head of NASA's Heliophysics Division, told Space.com. "It's a very strategic way that we're looking at this system [of instruments], as one large observatory."
Although the three missions weren't designed as a suite, they complement one another well. The Parker Solar Probe, which launched in August 2018, is flying closer to the visible surface of the sun than any spacecraft to date. That trajectory carries the spacecraft deep into the sun's atmosphere, called the corona, where the probe's instruments focus on the spacecraft's immediate surroundings, measuring magnetic fields and particles of plasma, the charged soupy state of matter that makes up the sun.
Solar Orbiter won't fly as close to the sun, but it brings unique skills. First, it carries two types of instruments. One set, like Parker's, will study the spacecraft's surroundings; the other, a set of telescopic instruments, will observe the visible surface of the sun itself at a distance. And partway through its mission, Solar Orbiter will leave the belt around the sun's middle, called the ecliptic, and begin circling the sun at a tilt, allowing the spacecraft to use those telescopic instruments to produce the first-ever images of the sun's poles.
The National Science Foundation's Inouye Solar Telescope is stuck here on Earth, and construction is still underway. But once all of its instruments are operational, there will be plenty more images like the "caramel corn" picture that scientists published in January — the highest-resolution solar image to date. "The Inouye Solar Telescope is a microscope on the sun," Valentin Martínez Pillet, director of the National Solar Observatory, which runs the facility, told Space.com. The observatory will also measure the wavelengths of light emitted by the sun and decipher the magnetic signature of light that is under the influence of the sun's magnetic field.
Although the three projects are separate endeavors, both scientists said they and their colleagues are awfully excited about pulling all the data together.
We have so few close-up observations of the sun that being able to compare two separate locations is automatically valuable, no matter where each spacecraft is. Solar Orbiter's final schedule was dependent on its precise launch date, but as mission personnel evaluated how each timetable aligned the spacecraft with the Parker Solar Probe's close approaches, they found intriguing opportunities regardless of the launch date, Fox said.
The Inouye Solar Telescope is even easier to integrate into an observational program, Martínez Pillet said; its personnel know precisely where the two spacecraft will be at any given time and can match up the telescope accordingly.
Combining the data from all three observatories is vital for scientists to accomplish the goal that drives the missions: to understand the sun and its influence throughout the solar system. The impacts of the sun's antics ripple across the solar system as a set of phenomena called space weather.
In Earth's neighborhood, space weather can interfere with the technology modern society is ever more reliant upon, particularly navigation and communication satellites. Space weather is also a hazard for astronauts traveling farther from Earth, as it can harm both their technology and their bodies. Ultimately, solar scientists want to be able to predict space weather in much the same way meteorologists predict terrestrial weather. "We are 50 or 100 years lagging from what terrestrial weather is in terms of prediction," Martínez Pillet said.
That's because scientists just don't know enough about how the sun works. "We're able to predict a single second on the sun," he said. "I'm exaggerating — well, no, I don't think I'm exaggerating. We're not able to have any realistic predictive capabilities today, but as soon as you get the physics right, then you start being able to develop predictive capabilities."
One particular challenge in understanding space weather is the sheer distance involved, and that's where the trio of missions will be valuable, Martínez Pillet said. "One space-weather event has a combination of scales," he said. "It's triggered at really small scales, and it's a huge thing that propagates all over the heliosphere and probably can hit several planets at the same time." But by the time space weather reaches Earth, it's been influenced by millions of miles of space; it's much fresher where the Parker Solar Probe and the Solar Orbiter can study it.
There's another reason to understand space weather: It could tell scientists where to look for signs of life elsewhere in the universe. After all, while we humans have a soft spot for the sun, it's just a star like any other — which means that scientists can apply what these three missions discover to all the stars we'll never be able to see as clearly. And while space weather is vexing to Earth, it could be deadly in solar systems that surround smaller, more active stars.
And there should be plenty for the trio of projects to study in the coming years. Right now, the sun is pretty quiet, but over the next five or six years, the sun's activity will increase — and both the Parker Solar Probe and the Solar Orbiter will be on hand to see what happens during that period.
"They are really, truly voyages of discovery, and we're doing fundamental physics and understanding how a star works," Fox said.
Of course, even three high-powered missions won't solve every mystery about the sun.
"We know right now what we don't know, but we're going to find a whole lot more things that we don't know," Fox said. "That's why it's nice that these missions are so long, so you have time to develop these new questions, this new thirst for knowledge."
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