Europe’s Solar Orbiter Begins Its Journey to the Sun

Just before midnight on Sunday, a spacecraft will depart from Cape Canaveral, Florida, on a mission to the sun. Known as Solar Orbiter, this spacecraft will spend the next seven years dipping in and out of the extremely inhospitable environment around the sun. In the process, it will provide us with our first glimpse of the sun’s poles, which will be critical to understanding its topsy-turvy magnetic field. It will also help uncover the origin of violent solar storms that send plasma hurtling toward Earth, where it can knock out satellites and disrupt our power grids.

The Solar Orbiter mission is spearheaded by the European Space Agency and has been almost two decades in the making. It complements NASA’s Parker Solar Probe, launched in 2018, which will pass closer to the sun than any spacecraft in history. Only a year into its mission, Parker is providing scientists with four times more data about the solar environment than expected, says Nour Raouafi, a heliophysicist at Johns Hopkins University Applied Physics Laboratory and Parker project scientist. “We are venturing into regions of space that we never explored before,” says Raouafi. “Every observation is a potential discovery.”

Solar Orbiter will augment Parker’s vast trove of data with an array of 10 instruments, which include six that can directly image the sun. This is a luxury unavailable to Parker, which passes too close to the sun to directly image it without instantly frying a camera’s sensors. But Parker and Solar Orbiter are both equipped with suites of instruments to study the environment around the sun, such as its magnetic field, its plasma ejections, and the irregular bursts of high-energy particles from the sun’s atmosphere, or corona.

Compared to Parker, Solar Orbiter will be keeping its distance from the sun, never venturing closer than about 26 million miles. This is just inside Mercury’s orbit, a hellish region of the solar system where the spacecraft will experience temperatures above 900 degrees Fahrenheit while being assaulted by high-energy particles belched out by the sun.

Solar Orbiter’s radiation-hardened instruments will be protected from the sweltering heat by a shield covered with doors that periodically open to allow the spacecraft’s instruments to image the sun. About half the size of an average parking space, the Solar Orbiter’s heat shield is a mix of modern and ancient technology. Its outermost layer is a strip of titanium just a fraction of a millimeter thick and coated on the sun-facing side with charred animal bone. This is the same stuff used by prehistoric humans to paint cave walls, but its properties also make it great for radiating heat away from a spacecraft.

Daniel Verscharen, an instrument scientist for Solar Orbiter, says he is particularly interested in what the craft will reveal about the solar wind, the plasma that is continuously flowing away from the sun’s corona. The particles in this plasma can reach speeds of more than 1 million miles an hour, but scientists aren’t sure how the solar atmosphere accelerates them to these high speeds. Solar wind is a constant aspect of space weather, somewhat like the air temperature on Earth. Sometimes the solar wind is strong, sometimes it’s weak, but it’s always there in the background.

And just like the Earth hosts the occasional extreme weather event, so does the sun. Known as coronal mass ejections, these solar storms can dump more than a billion tons of plasma into space at speeds that make the solar wind seem slow. This wave of sun stuff carries its own magnetic field along with it—and if it happens to pass over the Earth, the effect is like a mallet hitting a gong. When the plasma wave reaches Earth, it ripples across our own magnetic field in what is known as a geomagnetic storm.



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