Closest-ever images of the Sun reveal ‘campfires’ near the surface

The Solar Orbiter spacecraft has unveiled its first images, including what appear to be ubiquitous miniature solar flares.

The ‘campfire’ flares may solve a longstanding mystery about our star: why its outer atmosphere is hotter than its surface. The mini flares could also help scientists understand the dynamics of larger flares that can affect electronics and communications networks on Earth.

Teams from around the world are now working on all this data, which will no doubt reveal new insights into the Sun’s behaviour. Professor Tim Horbury

Solar Orbiter, a joint European Space Agency (ESA) and NASA mission, launched in February 2020 with an Imperial-built instrument on board. The data released today come from its first close pass to the Sun, flying around 77 million kilometres from the star, about half of the distance from the Earth to the Sun.

The spacecraft will get progressively closer over the next few years until it gets as close as 42 million kilometres, inside the orbit of Mercury. The first images however are already a record; no craft has flown closer to the Sun with cameras aboard.

Great results right from the start

Daniel Müller, ESA’s Solar Orbiter Project Scientist said: “These are only the first images and we can already see interesting new phenomena. We didn’t really expect such great results right from the start. We can also see how our ten scientific instruments complement each other, providing a holistic picture of the Sun and the surrounding environment.”

The ‘campfires’ were detected by the Extreme Ultraviolet Imager (EUI), which show the flares occurring across the surface of the Sun. These flares are millions or even billions of times smaller than solar flares that can be detected at Earth, but may hold the key to heating the Sun’s outer atmosphere.

The spacecraft carries six ‘remote sensing instruments’ that measure activity at the Sun, and four ‘in situ’ instruments that measure the space environment around the spacecraft. Linking these two sets of measurements can track the evolution of phenomena at the Sun as they expand into space, such as the stream of charged particles and magnetic field called the solar wind.

A team from Imperial built and run the magnetometer instrument, or MAG, an in situ instrument that measures the magnetic field from the Sun when it reaches the spacecraft. MAG was the first instrument to be turned on, shortly after launch, and has been collecting data for more than 100 days, amassing over two billion measurements of the Sun’s magnetic field as it reaches the spacecraft.

These will be analysed and compared with measurements from different instruments, particularly the Polarimetric and Helioseismic Imager (PHI), which makes high-resolution measurements of the magnetic field lines on the surface of the Sun. It is designed to monitor active regions on the Sun, areas with especially strong magnetic fields, which can give birth to solar flares. Once detected at the Sun, MAG could trace how the magnetic field associated with these flares evolve as they move through space towards the Earth.

Five views of the Sun captured with the Extreme Ultraviolet Imager (EUI) and Polarimetric and Helioseismic Imager (PHI) instruments on ESA’s Solar Orbiter.  For full description see bottom.

New insights into the Sun's behaviour

Principal Investigator for the MAG instrument, Professor Tim Horbury from the Department of Physics at Imperial, said: “Already our data are revealing shockwaves, coronal mass ejections, phenomena called ‘switchbacks’ and fine-scale waves in the magnetic field that we are only able to see thanks to the extreme sensitivity of our instrument.

“Our small team of engineers here at Imperial College London have been working really hard to keep the instrument operating and process all the measurements that are coming down to the ground. Teams from around the world are now working on all this data, which will no doubt reveal new insights into the Sun’s behaviour.”

Instrument Manager for MAG, Helen O’Brien from the Department of Physics at Imperial, said: “The engineering team are absolutely loving this. We spent so long designing, building and testing this instrument, that to finally to be collecting science data every day, seeing all this structure in the magnetic field, is fantastic.

"No day is the same when you are travelling at 90,000 mph. Taking measurements, in tandem with nine other instruments, is exactly where we want to be.”

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Full GIF caption: 

This animation shows five views of the Sun captured with the Extreme Ultraviolet Imager (EUI) and Polarimetric and Helioseismic Imager (PHI) instruments on ESA’s Solar Orbiter.

The first two views were taken with EUI’s Full Sun Imager (FSI) taken across the week following 30 May 2020. The yellow image shows the Sun’s outer atmosphere, the corona, which exists at a temperature of around one million degrees. The red image shows the Sun’s transition region, which is an interface between the lower and upper layers of the solar atmosphere. In this region, which is only about 100 km thick, the temperature increases by a factor of up to 100 to reach the one million degrees of the corona.

The third, fourth and fifth views are based on data taken with PHI on 18 June 2020.

The third view is a ‘tachogram’ of the Sun, showing the line of sight velocity of the Sun, with the blue side turning to us and the red side turning away. The fourth view is a magnetogram, or a map of magnetic propertied for the whole Sun, featuring a large magnetically active region in the lower right-hand quadrant of the Sun. The fifth view is a visible light image and represents what we would see with the naked eye. There are no sunspots visible because the Sun is displaying only low levels of magnetic activity at the moment. 

Credit: Solar Orbiter/EUI Team; PHI Team/ESA & NASA