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EXPLORING ENERGY RELEASE
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, 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
The project team at the Solar Orbiter launch.
solar system. What causes the different types of solar wind? How are they accelerated away from the Sun?
says there have already been some interesting observations. “One of the new things that has been seen are very tiny features in the extreme ultra-violet images, where material is being thrown out on a really small scale, which could end up in the solar wind. The smaller the scale at which we can observe the Sun, the more we see that the Sun is active,” she says. The Sun’s activity cycle lasts around 11 years, and different stages will be observed over the course of the mission, while Professor Harra says they will also observe different regions. “We used gravitational energy from Earth and Venus to alter the orbit of the satellite so that we’ll be able to peer down at the poles of the Sun,” she explains.
Peering at the poles
This is entirely new territory in research, as the poles of the Sun have never been observed before.
Currently researchers are relatively limited in their understanding of the poles, which limits their ability to model the Sun’s activity. “The Sun’s activity cannot yet be modelled accurately, partly because we won’t know what the polar magnetic field looks like in detail,” outlines Professor Harra. The view of the poles will become clearer over time as the satellite’s orbit gradually shifts upwards, and the highest point will be reached around 2027 or 2028, helping researchers get a fuller picture of what the magnetic field looks like at the poles. “It’s not simply all positive or negative magnetic field, we know that it’s much messier than that, so we’re really looking forward to getting our first glimpse of the poles,” continues Professor Harra. “As both Parker Solar probe and Solar Orbiter get closer to the Sun we will see more energetic particles, and see more of the underlying dynamics.”
This is a very exciting time in solar research, with scientists set to break entirely new ground over the next few years as more images and data are provided from the two satellites, while the early images are also proving very interesting. The first images from the Solar Orbiter show miniature flares which have been called campfires close to the surface of the Sun. “These are tiny events that haven’t been seen before. We saw those in our first perihelion – the closest point to the Sun in the satellite’s current orbit – and as we get closer to the Sun we’ll see many more of those,” says Professor Harra.
These images show a series of views of the Sun captured with the Extreme Ultraviolet Imager (EUI) on ESA’s Solar Orbiter on 30 May 2020. © ESA They show the Sun’s appearance at a wavelength of 17 nanometers, which is in the extreme ultraviolet region of the electromagnetic spectrum. Images at this wavelength reveal the upper atmosphere of the Sun, the corona, with a temperature of around 1 million degrees.
Exploring energy release from magnetic fields from small to large scales Project Objectives
The main objective is to understand how solar activity at all scales creates the heliosphere.
Project Funding
SNSF funding for current research at PMOD/ WRC and ETH in solar physics: 347,394 CHF.
Project Partners
Solar Orbiter: ESA, NASA • EUI: PMOD/ WRC, ROB, IAS, MPS, CSL, UCL-MSSL • ISSI: This work is also part of the ISSI international team’Exploring The Solar Wind In Regions Closer Than Ever Observed Before’ • NASA Parker Solar Probe team
Contact Details
Principal Investigator, Professor Louise Harra Director Physikalisch-Meteorologische Observatorium Davos/World Radiation Center (PMOD/WRC) Dorfstrasse 33 CH-7260 Davos Dorf Switzerland T: +41 81 417 51 24 E: louise.harra@pmodwrc.ch W: https://www.pmodwrc.ch/en/institute/ employees/louise-harra/ Affiliated Professor at ETH-Zürich ETH-office: Hönggerberg campus, HIT building, J22.4 T: +41 44 633 44 50
Professor Louise Harra
Professor Louise Harra is a solar physicist researching the activity on the Sun. I was PI of Hinode EIS from launch in 2006 until 2019. I am co-PI of EUI on the ESA Solar Orbiter mission which was launched in 2020. I am based at PMOD/WRC in Davos and ETH-Zürich in Switzerland.
