A Mission to the Sun Left Just in Time

The spacecraft, launched earlier this year, has returned stunning views of our star.

Solar Orbiter / EUI Team (ESA & NASA) / CSL / IAS / MPS / PMOD / WRC / ROB / UCL / MSSL

For Daniel Müller, a solar physicist at the European Space Agency, there are two suns. There’s the one that hangs in the sky and warms his skin as he walks along the coastline near his home in the Netherlands. And there’s the one that exists indoors, on his computer screen, which he can stare at for hours, studying the swirls in a fiery landscape.

As much as he enjoys a sunny walk on the beach, Müller has been basking in the other version of our star this summer: A recently launched spacecraft has captured the closest images ever taken of the sun and sent them back to Earth.

The images show the sun in glowing detail. They were captured by telescopes on Solar Orbiter (a delightfully straightforward name for a mission) as the spacecraft zoomed past the sun. The hot plasma resembles a portrait of storm clouds rendered in gold tones.

To the untrained eye, these are pretty pictures, but to scientists such as Müller, they might provide important information about a star that, despite its close proximity and decades of research, the scientific community is still trying to understand.

Take a closer look at the images from Solar Orbiter and you’ll see sparks of light nestled in the plasma swirls. Each pinprick is a solar flare, an explosion of energy most likely caused by the tangling of magnetic fields.

Solar Orbiter / EUI Team (ESA & NASA) / CSL / IAS / MPS / PMOD / WRC / ROB / UCL / MSSL

On Earth, these smaller flares could stretch from Washington, D.C., to New York City. By the sun’s standards, they are tiny, producing only about a billionth of the energy of flares that can be detected from the ground and even temporarily knock out our communications.

The miniature flares could help explain the nature of the outermost layer of the sun’s atmosphere, a region visible to us only during a solar eclipse, as a milky-white ring in a darkened sky. Known as the corona, this layer is, paradoxically, far hotter than the sun’s surface: It’s nearly 2 million degrees Fahrenheit (more than 1 million degrees Celsius), while the surface is a comparatively cool 9,900 degrees Fahrenheit (about 5,500 degrees Celsius). Observations have shown that the same is true for other sunlike stars, but our own star provides the best option for investigating why that is; after all, the sun is the only star we’re likely to ever get this close to.

The flares flicker in the depths of the corona, just above the sun’s surface, and the new photos suggest that the sun is covered in them. The phenomena might fit a theory that the solar physicist Eugene Parker proposed decades ago, when telescope technology wasn’t sophisticated enough to acquire these kinds of views. Parker hypothesized that magnetic interactions would spark a flurry of small flares near the surface of the sun—nanoflares, as he called them. These flares could produce enough energy to raise the corona’s temperature to scorching heights.

“A few of them together do not create a lot of heat or energy,” says Holly Gilbert, a NASA solar physicist who works on the mission. “If you combine them all together, it’s possible that that is contributing to the coronal heating.”

The corona is one of several conundrums at the center of our solar system. Scientists have yet to pin down the mechanism that fuels the sun’s biggest flares, or that unleashes solar wind toward Earth and beyond, past planets and moons, to the solar system’s invisible edges, where the high-energy stream starts mixing with the cooler particles of interstellar space.

Solar Orbiter, which is operated by the European Space Agency and NASA, left Earth just in time. The mission departed in mid-February, weeks before authorities started issuing stay-at-home orders because of the coronavirus in Europe, where the spacecraft was manufactured, and the United States, where it was launched. Hundreds of employees from the two space agencies traveled to Cape Canaveral for the launch and celebrated together in the kind of gathering that would be banned today.

In the months since, only two spacecraft operators have been allowed into the ESA’s control rooms at the same time, and always in face masks. Scientists who had planned to be in the room with them, to help get the spacecraft’s instruments online and working, guided the operators over video instead. “We were very worried at the beginning,” says José-Luis Pellón-Bailón, the mission’s deputy spacecraft-operations manager and one of the few people still permitted to enter the control room.

If space agencies had fallen behind schedule in February and missed the window to put Solar Orbiter on the best trajectory, they would have had to wait until October to launch. The pandemic has already slowed down other space projects, and contributed to a two-year launch delay for a Mars rover, which depends on cosmic alignments for its journey. When Müller considers this alternate reality, in which Solar Orbiter sits in a warehouse instead of coasting through space, he nearly shudders. “No one knows what the world will look like in October,” he said.

Today, Solar Orbiter’s instruments are running smoothly. The spacecraft is currently hurtling away from us and toward Venus, where it will steal some of the planet’s gravity to adjust its orbit and swing closer to the sun. (It sounds strange, but flying into the sun is actually harder than leaving the solar system.) Officials haven’t yet decided how, years from now, the mission will end. They could leave the spacecraft gliding in space, or they could plunge it into the sun, as NASA is planning to do with another sun-observing spacecraft, named for Parker, the longtime physicist. That probe will get even closer to the sun, but it doesn’t have telescopes that can look directly at the star, as Solar Orbiter does.

Solar Orbiter will make its next close approach to the sun early next year, loaded with commands to carry out a picture-perfect flyby. Scientists expect the spacecraft to catch even better views of the miniature flares they found this summer, and perhaps other intriguing features too. Maybe, by then, more than two people will be allowed in the control room, to guide the spacecraft’s course. On Earth, trajectories large and small—the course of a deadly virus, the minutiae of daily life—can’t be so easily programmed and planned.