Solar Orbiter's EUI Camera 'Hack' Lets Scientists See Deeper Into Sun's Atmosphere

Scientists have used Solar Orbiter's Extreme Ultraviolet Imager (EUI) in a new mode of operation to record part of the sun's atmosphere at extreme ultraviolet wavelengths that has been almost impossible to image until now. This new mode of operation was made possible with a last-minute "hack" to the camera and will almost certainly influence new solar instruments for future missions.

Regular 10 s exposure time 17.4 nm FSI image taken at 0.68 au from the sun on 2022 March 23 at 23:01. At this distance, the FOV extends to 4.9 R⊙. With this exposure time, signal is detected up to 2 R⊙. Longer exposures and the use of an occulting disk are required at larger angles. The cause of the two vertical dark bands has not yet been identified. Credit: Astronomy & Astrophysics (2023). DOI: 10.1051/0004-6361/202346039

Solar Orbiter is a European Space Agency (ESA) mission that was launched in February 2020 to study the sun from closer than ever before. The EUI instrument is one of Solar Orbiter's 10 science instruments, and it is designed to image the sun's atmosphere, or corona, in extreme ultraviolet light.

The corona is a million times fainter than the sun's surface, so it is very difficult to image. In the past, images of the corona have been taken with dedicated instruments called coronagraphs. Coronagraphs work by blocking out the light from the sun's surface, so that the fainter light from the corona can be seen.

The EUI occulter mode is a new way of imaging the corona that does not use a coronagraph. Instead, it uses a small, protruding "thumb" on the front of the EUI instrument to block out the light from the sun's surface. This allows the EUI instrument to detect the million-times fainter ultraviolet light coming from the surrounding corona.

The EUI occulter mode has been tested since 2021, and the team is confident that it is working well. They have published a paper in the journal Astronomy & Astrophysics describing the results of their tests.

The EUI occulter mode is a significant breakthrough in solar imaging. It allows scientists to see deeper into the sun's atmosphere than ever before, and it will help them to better understand the physics of the corona. The EUI occulter mode is also likely to influence the design of future solar instruments.

"This is a really exciting development," said Daniel Müller, ESA's project scientist for Solar Orbiter. "It opens up a new window on the sun's atmosphere, and it will help us to answer some of the big questions about the sun."

The EUI occulter mode is just one of the many ways that Solar Orbiter is helping scientists to understand the sun. The mission is scheduled to continue until 2030, and it is expected to make many more discoveries about our nearest star.

Journal Information: F. Auchère et al, Beyond the disk: EUV coronagraphic observations of the Extreme Ultraviolet Imager on board Solar Orbiter, Astronomy & Astrophysics (2023). DOI: 10.1051/0004-6361/202346039