A long, oddly shaped gap in the Sun’s corona.
Solar Dynamics Observatory / NASA
In this image taken on 22 December 2017, an elongated coronal hole on the Sun (the darker area near the centre of the picture) takes the shape of a single, recognisable question mark.
Coronal holes are areas of open magnetic field that appear darker in extreme ultraviolet light, as is seen here. These holes are the source of the streaming plasma we call solar wind.