ESA Solar Orbiter – Close Encounters of the Sun
An artist’s impression of Solar Orbiter around the Sun. Credit: ESA

ESA Solar Orbiter – Close Encounters of the Sun

27/03/2022Written by Dhara Patel

ESA's Solar Orbiter is a European flagship mission to study the Sun and the effects of solar activity within its realm.

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It’s the sustainer of life on Earth yet has the ability to send the world into a state of disarray; studying our Sun – its cyclic nature and its violent outbursts, has never been more important. Working in collaboration with NASA, the European Space Agency (ESA) hopes to help answer the question of how the Sun creates and controls the ever-changing space environment within the Solar System known as the heliosphere. 

Solar Orbiter - In a Nutshell

Solar Orbiter - In a Nutshell
Satellite technology is critical to modern civilisation, but they are at the mercy of space weather directed by the Sun. Credit: ESA
Solar Orbiter - In a Nutshell
Animation of a part of Solar Orbiter's highly inclined orbit. Credit: ESA/ATG medialab

Launched in February 2020, ESA’s Solar Orbiter mission is the most complicated science laboratory that’s ever been sent to the Sun. The Sun is responsible for our space weather and so understanding it is key to protecting our planet, and the satellite infrastructure orbiting Earth that we’re so dependent on for our daily activities. But the Sun’s immense gravitational pull and highly energetic nature make travelling to and studying it up-close incredibly challenging.  

In spite of that, after making several fly-bys of Venus followed by a risky gravity assist from the Earth to shift its orbit closer to the Sun, Solar Orbiter was able to commence its scientific mission in November 2021. And on 26 March 2022, it reached its closest approach to the Sun to date – less than 50 million kilometres, which is less than a third of the Earth-Sun distance and well within the orbit of Mercury. 

Due to its inclined and elliptical orbit, the spacecraft will be able to capture views of the Sun’s polar regions – an endeavour that’s never been achieved before, and it will make a close approach to the Sun roughly every six months providing views of 180 kilometres-wide details on the surface. By measuring what the solar wind is made of and linking that to where on the Sun it originates from, scientists will be able to better understand the Sun’s inner workings. 

Designing and Building the Spacecraft

Designing and Building the Spacecraft
Solar Orbiter at Airbus Defence and Space, Stevenage, UK. Credit: Airbus Defence and Space
Designing and Building the Spacecraft
Solar Orbiter’s remote sensing and in situ instruments. Credit: ESA-S. Poletti
Designing and Building the Spacecraft
Launched on an Atlas 5 rocket, Solar Orbiter began its journey to the Sun lifting off from Cape Canaveral Air Force Station, Florida in February 2020. Credit: United Launch Alliance

The contract to build Solar Orbiter was awarded to Astrium UK in 2012 and in the following year, a merger including this aerospace manufacturer led to the formation of Airbus Defence and Space. Leading a group of European companies to supply different parts of the spacecraft, Solar Orbiter was designed and built right here in the UK by Airbus Defence and Space in Stevenage.  

Solar Orbiter has ten instruments, six of those are remote sensing, so they are cameras observing the Sun and providing imagery. The remaining four are in situ instruments which take measurements of the environment around the spacecraft like the electrified gas emanating from the Sun known as the solar wind. Two of those four in situ instruments were built in the UK. 

The magnetometer to measure the strength and direction of the magnetic field surrounding the spacecraft was built by Imperial College London. And to help scientists understand what the solar wind is made of, the Solar Wind Analyser Suite which measures more than 99% of the charged particles that come to the spacecraft from the Sun, was manufactured at Mullard Space Science Laboratory in Dorking. 

Following its construction in Stevenage, Solar Orbiter spent a year at the German IABG test engineering facility to ensure it was able to cope with the vibrations of launch, as well as thermal extremes of more than 500 degrees Celsius and the vacuum environment which it would experience in space. And by October 2019 it was ready to be shipped to Cape Canaveral in the United States from where it launched. 

Teamwork with NASA's Parker Solar Probe

Teamwork with NASA's Parker Solar Probe
An artistic impression of Solar Orbiter (left) and Parker Solar Probe (right) – not to scale. Credit: Solar Orbiter: ESA/ATG medialab; Parker Solar Probe: NASA/Johns Hopkins APL
Teamwork with NASA's Parker Solar Probe
Artist concept showing the layers of the Sun. Credit: NASA

Although Solar Orbiter is an ESA mission, it is a complimentary study of the Sun to NASA’s Parker Solar Probe which launched in August 2018. While Parker Solar Probe will venture much closer to the Sun (passing within just 6.2 million kilometres of the Sun’s surface in the final orbits of its mission), it doesn’t have any cameras as we don’t have the technology able to survive the extreme conditions it would be subject to while operating so close to our star. It instead has a few instruments that will focus on sampling the corona (the outermost layer of the Sun), specifically the region where material from the corona detaches to become the solar wind. 

Meanwhile Solar Orbiter will study the Sun from a more distant orbit with a wide range of detectors. And because both missions may collect data over the same areas during points throughout their mission durations, the broader findings from Solar Orbiter will hopefully help put the close-range measurements from the Parker Solar Probe into context. With Solar Orbiter’s suite of instruments and Parker Solar Probe’s up-close analysis of the Sun, we’ll be treated to a comprehensive global view of our star. 

Achievements to Date

Achievements to Date
Solar Orbiter serendipitously flew through the tail of Comet Leonard in December 2021. Credit: University of Hertfordshire Observatory
Achievements to Date
Stunning image from Solar Orbiter capturing a solar prominence eruption 15 February 2022. Credit: ESA

By lucky chance, the spacecraft managed to fly through the tails of two comets as it journeyed into its inclined orbit around the Sun. The second encounter which saw Solar Orbiter speed through the tail of Comet Leonard took place for several days around 17 December 2021. Although the comet’s nucleus was some 44.5 million kilometres away, its giant tail stretched across space allowing scientists to study how this ‘dirty snowball’ interacts with the solar wind. The first pass was through the tail of Comet Atlas at the end of May 2020, and it was the first time a spacecraft flyby through a comet tail was predicted in advance – all previous occasions of non-comet chasing missions achieving the same feat were discovered in spacecraft data after the fact. 

And about a month before reaching its first close approach to the Sun, Solar Orbiter captured a massive solar eruption, and it’s the largest one observed in a single image with the full solar disc in view. Eruptions occur when a solar prominence (a large structure of densely packed plasma suspended above the Sun’s surface, which is kept locked and tangled by its magnetic field lines) is unleashed into space. The Full Sun Imager instrument which captured this stunning view on 15 February 2022 will be able to observe the full solar disc even at its closest approach, though the Sun will just fill a bigger portion of the telescope’s field of view. 

ESA’s Solar Orbiter mission is essential to understanding the central powerhouse of our Solar System and in the years to come we’ll hopefully be better equipped to reduce the risks that space weather has on Earth and it’s thanks to the data and observations that this spacecraft will provide.  

About the author: Dhara Patel is a Space Expert at the National Space Centre.