Space mission flies close to the sun The Solar Orbiter satellite will provide images of the Sun from closer than ever before, just 42 million kilometres away at its closest point, which will help scientists learn more about the Sun and the surrounding heliosphere. We spoke to Professor Louise Harra about her research into how energy is released from magnetic fields on the Sun at different scales. The Solar Orbiter satellite was launched by the ESA and NASA in February 2020, and reaches its operational orbit around the Sun at the end of 2021. Over the course of the mission the satellite will send back images of the Sun and the surrounding heliosphere, from which Professor Louise Harra and her colleagues hope to gain new insights into how energy is released from magnetic fields on the Sun at different scales. “We’re looking at how the heliosphere is created and how does the solar wind accelerate into the rest of the solar system. What causes the different types of solar wind?” she outlines. The Sun is currently becoming more active as it comes out of its quiet phase, and some interesting data has already been gathered during the early stages of the mission. “With Solar Orbiter we have caught quite a number of flares at the far side of the Sun during this cruise phase,” says Professor Harra. Many more images will be taken over the next few years, with the satellite set to take images from closer to the Sun than ever before, just 42 million kilometres away at its closest point. This will allow researchers to analyse the solar wind – the charged particles flowing away from the Sun – in unprecedented detail. “The solar wind is split into two categories – fast and slow. The fast wind is fast and steady, whereas the slow wind is slower and fluctuates much more rapidly,” explains Professor Harra. Images from closer in to the Sun reveal that the solar wind is more complex than had previously been thought. “The closer you get, the more dynamic the solar wind becomes. We can see that the general perception of the solar wind as a sort of steady state wind is probably not correct, it’s a lot more dynamic” says Professor Harra. “We’re also working with data gathered from NASA’s Parker Solar Probe mission.”
Solar wind Researchers know that the fast solar wind comes from coronal holes in the plasma around the Sun, yet the origins of the slow wind are less clear, a major area of interest to Professor Harra. It is difficult to interpret evidence of slow wind gathered on earth,
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The project team at the Solar Orbiter launch.
We’re looking at how
the heliosphere is created and how the solar wind accelerates into the rest of the solar system. What causes the different types of solar wind? How are they accelerated away from the Sun? as it interacts with other sources of wind, underlining the benefits of getting close in to the Sun. “We can look at this slow solar wind at an early stage, when it’s just been formed,” stresses Professor Harra. There are 10 different instruments on the Solar Orbiter, including telescopes and remote sensing instruments, while various measurements are also being taken. “There are also in situ measurements that are measuring the magnetic field and the solar wind, as it flows past the spacecraft,” outlines Professor Harra. “The in situ measurements can be on all the time throughout the mission, but the telescopes are on only during periods of key scientific interest such as when we’re close to the Sun – this is due to telemetry constraints..” One of the biggest technical challenges in the project was to develop a heat shield to protect the instruments so that they can withstand the extreme environment when close to the the Sun. The satellite is still
at an early stage of its journey, and when it does enter its scientific orbit, Professor Harra and her colleagues will be selective in how they use the instruments. “Each orbit lasts around 180 days, and within that orbit we’ve got three 10-day windows where we’ll observe using all the instruments,” she says. This will give researchers the opportunity to investigate the source of the solar wind. “Is the source from regions where you’ve got very extended, expanded open magnetic field lines?” asks Professor Harra. “Or is it from an interaction, high up in the corona, as its expanding away? Or does it actually come from lower down on the surface, where smaller-scale jets interact?” The spacecraft is currently in its cruise phase, so it’s only providing tiny snapshots of data for scientists to check that the instruments are operating properly, and to work on calibration. However, there is enough data to do some research, and Professor Harra
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