Northumbria University working to uncover last space mystery

A team from Northumbria University, in Newcastle led by Dr Steph Yardley are looking into the origins of ‘slow’ solar wind, using data collected during the Solar Orbiter spacecraft’s first close journey to the Sun.

Solar wind describes the continuous outflow of charged plasma particles from the Sun into space – with wind travelling at over 500km per second known as ‘fast’ and under 500km per second described as ‘slow’.

When this wind hits the Earth’s atmosphere it can result in the stunning aurora we know as the Northern Lights. But when larger quantities of plasma are released, in the form of a coronal mass ejection, it can also be hazardous, causing significant damage to satellites and communications systems.

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In 2020 the European Space Agency (ESA), with support from NASA, launched the Solar Orbiter mission. As well as capturing the closest and most detailed images of the Sun ever taken, one of the mission’s main aims is to measure and link the solar wind back to its area of origin on the Sun’s surface.

Dr Yardley explains: “The variability of solar wind streams measured in situ at a spacecraft close to the Sun provide us with a lot of information on their sources, and although past studies have traced the origins of the solar wind, this was done much closer to Earth, by which time this variability is lost.

“Because Solar Orbiter travels so close to the Sun, we can capture the complex nature of the solar wind to get a much clearer picture of its origins and how this complexity is driven by the changes in different source regions.”

The difference between the speed of the fast and slow solar wind is thought to be due to the different areas of the Sun’s corona, the outermost layer of its atmosphere, that they originate from.

An image of the Sun's south pole taken by Solar Orbiter (Image: Northumbria University)

Using the instruments onboard Solar Orbiter, the team were able to analyse the activity taking place on the surface of the Sun and then match this with the solar wind streams collected by the spacecraft.

The ESA Solar Orbiter mission is an international collaboration, with scientists and institutions from around the world working together, contributing specialist skills and equipment.

Daniel Müller, ESA Project Scientist for Solar Orbiter, said: “From the beginning, a central goal of the Solar Orbiter mission has been to link dynamic events on the Sun to their impact on the surrounding plasma bubble of the heliosphere.

“To achieve this, we need to combine remote observations of the Sun with in-situ measurements of the solar wind as it flows past the spacecraft. I am immensely proud of the entire team for making these complex measurements successfully.

“This result confirms that Solar Orbiter is able to make robust connections between the solar wind and its source regions on the solar surface. This was a key objective of the mission and opens the way for us to study the solar wind’s origin in unprecedented detail.”

The electrons in the solar wind are measured by an Electron Analyser System developed by University College London's Mullard Space Science Laboratory, where Dr Yardley is an Honorary Fellow.

Professor Christopher Owen, of UCL, said: “The instrument teams spent more than a decade designing, building and preparing their sensors for launch, as well as planning how best to operate them in a co-ordinated way. So it is highly gratifying to now see the data being put together to reveal which regions of the Sun are driving the slow solar wind and its variability.”

Speaking about future research plans, Dr Yardley said: “So far, we have only analysed Solar Orbiter data in this way for this particular interval. It will be very interesting to look at other cases using Solar Orbiter and to also make a comparison to datasets from other close-in missions such as NASA’s Parker Solar Probe.”