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The European Space Agency's “Smile” mission aims to observe how the Sun and Earth interact

The European Space Agency's “Smile” mission aims to observe how the Sun and Earth interact

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The first joint European-Chinese mission, “Smile,” is scheduled to be launched into space at the end of 2025 on board the Vega-C rocket.

FRANKFURT – The Sun is not just the fixed star in our solar system around which the Earth revolves and without which life would not be possible. There are also ongoing interactions between them and our home planet, especially between solar wind particles and Earth's magnetic shield, the magnetosphere. Better understanding this complex interaction is the goal of “Smile,” a joint mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CIA), which is expected to start at the end of 2025 and last for three years. (“Smile” stands for “Solar Wind-Magnetosphere-Ionosphere Link Explorer.”)

It was also recently signed that transportation to space will take place on a European Vega-C rocket from the spaceport in French Guiana. Carol Mundell, ESA's director of science, spoke of “an important milestone for this innovative mission.”

The European Space Agency's “Smile” mission aims to investigate the relationship between the Sun and the Earth

“Smile” aims to be the first probe that studies not only individual aspects, but the relationship between the Sun and the Earth comprehensively. It is also the first mission undertaken by the European Space Agency China Planned and executed together from start to finish. Scientifically, it follows China's Double Star/Tan Ce mission, which flew between 2003 and 2008 and was supported by the European Space Agency.

The magnetosphere (right) protects the Earth from the Sun and its powerful forces. Issa © Issa

The Vega-C rocket initially aims to place the “Smile” satellite, which weighs more than 2,000 kilograms, into low Earth orbit. From there, the probe must drift independently to its final elliptical orbit, which is at a higher altitude. It takes about 40 hours to orbit around the Earth. “Smile” will fly over the North Pole region from a distance of 121,000 kilometers, equivalent to about a third of the distance to the moon. The satellite then descends to an altitude of 5,000 kilometers to send the trove of acquired data to ground stations in Antarctica and China.

The “Smile” probe aims to show how the solar wind collides with the Earth's magnetosphere

From its orbit, the probe will take the first X-ray images and videos showing how the solar wind collides with the magnetosphere that surrounds and protects the Earth like a bubble. The solar wind is a stream of energetic particles that the Sun constantly sends into space in addition to its radiation. If this flow of particles is stronger than normal in an area for a certain period of time, it is called a solar flare.

Subsequent phenomena that are triggered are referred to as solar storms. But the “normal” solar wind also has visible effects on Earth: if charged solar particles collide with the magnetic field, they are compressed in some places and pushed outward in others, and the particles in turn are directed toward the poles. On Earth, molecular rain can appear as northern lights.

The effects of the solar wind appear mostly in the north

Solar wind effects are mostly strongest in the Arctic, Iceland, Greenland, northwestern Russia, and Finland. Strong solar storms can also leave their mark even in Central Europe. The Smile probe will continuously take ultraviolet images of the northern lights from its orbit as it flies over the corresponding regions. This will be the first opportunity for scientists to observe these key phenomena of “Sun-Earth interaction” continuously over a long period of time, as can be read on the ESA home page.

The optical ion analyzer on board the probe is an instrument designed to analyze the behavior of the solar wind.
The optical ion analyzer on board the probe is an instrument designed to analyze the behavior of the solar wind. © Issa

The satellite is equipped with four devices from Europe, Canada and China. The new “soft wide-field X-ray imager” will take measurements in those regions where the solar wind affects the magnetosphere. The mission of the Ultraviolet Imager is to study the global distribution of the northern lights; Optical ion analyzers and magnetometers aim to measure high-energy particles in the solar wind and changes in areas affected by the magnetic field.

Other sensors have already observed the Sun's effect on Earth

Before Smile, several other missions had observed the Sun and its effects on Earth. However, these studies have largely looked at “local processes and individual space weather events,” says ESA. On the other hand, “Smile” will be able to see “the complete contact between the Sun and the Earth,” thus filling a “big gap” in the exploration of the solar system.

To date, three fundamental questions in the interaction between the Sun and Earth have not yet been fully answered: What happens when the solar wind hits the Earth's magnetic shield? What causes magnetic disturbances on the dark side of the Earth? And – of direct importance to life on Earth: How can we predict the most dangerous threats from space weather?

A deeper understanding of these processes will be important in order to better protect both the technology now widely in orbit and the astronauts on the ISS. Strong solar winds and solar storms can disrupt air traffic, but they can also severely impact power supplies, cell phone networks, or GPS systems. (bam)