The camera’s “hack” allows the Solar Orbiter to peer deeper into the sun’s atmosphere

Science and exploration

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Scientists used the Solar Orbiter’s EUI camera in a new mode of operation to record a portion of the sun’s atmosphere at extreme ultraviolet wavelengths that until now have been nearly impossible to image. This new mode of operation was made possible by a last-minute camera “hack” and is sure to influence new solar instruments for future missions.

The Solar Orbiter’s Extreme Ultraviolet Imager (EUI) returns high-resolution images of structures in the sun’s atmosphere. Scientists call this region the corona. During the construction of the EUI, a last-minute modification allowed the safety door on the front of the device to see through the target area deeper than originally intended.

“It was a real breakthrough,” says Frédéric Aucher, from the Institute of Astrophysics at Paris-Sud University and a member of the EUI team. “I came up with the idea to do this and see if it worked. It’s actually a very simple modification to the tool.

This involved adding a small protruding “thumb”, weighing a few grams, to the door of the instrument. When the door slides away to let light into the camera, if it’s stopped halfway, the thumb covers the sun’s bright disk, and EUI can detect light a million times dimmer in ultraviolet coming from the surrounding corona.

The team refers to this as the mystery mode of operation. Tests with EUI occulter have been ongoing since 2021. Now the team is confident that it will work and has written a paper and published a video showing the results.

A new way to see the sun

The film shows an ultraviolet image of the sun’s corona taken with the EUI obscurant instrument. An ultraviolet image of the sun’s disk is superimposed in the centre, in the area left blank by the blocking. The image of the sun’s disk was taken by NASA’s STEREO mission, which happened to be looking at the sun from roughly the same direction as the Solar Orbiter at the same time, so features on the surface have a good correlation with features in the corona.

In the past, images of the sun’s corona were taken with specialized instruments called coronagraphs. For example, the solar orbiter’s coronagraph is called Metis. The value of this new approach is that the chronograph and camera can be included in the same instrument.

“We’ve shown that this works so well that you can now think of a new type of instrument that can image the sun and its corona,” says Daniel Müller, ESA’s Solar Orbiter project scientist.

And even before these new tools, there is a lot of new science that will come from the EUI. The mysterious mode allows scientists to see deeper into the sun’s atmosphere. This is the area that is outside the field of view of classical UV imagers but is usually obscured by conventional corona imagers. However, the EUI masking tool can now easily visualize this little-explored area.

“The physics is changing there, the magnetic structures are changing there, and we’ve never had a good look at it before. There must be some secrets that we can find now,” says David Bergmans, Royal Observatory of Belgium and EUI principal investigator.

Solar Orbiter is a space mission of international cooperation between the European Space Agency and NASA, and is operated by the European Space Agency.

Notes to editors:
Beyond the Disk: Coronal Ultraviolet Ultraviolet Imaging Observations of the Extreme Ultraviolet Imager aboard the Solar Orbiter by F. Auchère et al. Published in Astronomy and astrophysics Volume 674, June 2023.

For more information, please contact:
Media relations for the European Space Agency

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