What does the north pole of the Sun look like?
This might not be one of the most pressing questions in astronomy, but it has been intriguing solar physicists for a while. We've sent many probes to study the Sun at a wide range of latitudes but never actually from above or below, so there’s a gap in our knowledge of our star, which we may now be able to start filling in.
Using data from the Proba-2 (PRoject for OnBoard Autonomy 2) observatory, the European Space Agency (ESA) has managed to create an image of how the north pole of the Sun is likely to look.
So, without directly photographing it, how did they do it?
Proba-2 focuses mainly on the lower latitudes of the Sun but it captures everything in its line of sight, including solar atmospheric effects at high latitudes, which can indirectly help us understand the polar regions.
The team took observations of the Sun, blocking out the solar disk, and leaving only the northernmost part (and a bit on the sides) – as demonstrated by this handy comic strip-style illustration below. These were converted into information about the atmospheric situation at the time the image was taken. The process was then repeated several times at later times until there was enough data to cover roughly half of a solar rotation. And from that, they were able to reconstruct the image above.
Such a reconstruction is not certainly a true image – some imprecisions are evident, such as the big line across the middle, which is due to changes to the solar atmosphere as the observations were taking place – but it is the best we can hope for, for now.
Dark and light patches are seen on the surface, indicating that the complexity of our star extends to all latitudes. The dark patch in the middle is a polar coronal hole, the source of a fast solar wind. The image is from extreme ultraviolet light, so it tracks the energetic processes that give rise to the solar wind, the particles that stream from the Sun out into the Solar System. The network of structure seen here could alter the solar wind speed.
The NASA/ESA Ulysses mission back in 1994/1995 was the only probe we've sent to study the polar regions of the Sun, but It won’t be the last. ESA is planning to send a new mission in 2020. The Solar Orbiter will study the Sun at high enough latitudes that it will be capable of exploring its polar regions. This knowledge will be very important in understanding several processes happening on the Sun’s surface and how they impact the space environment around Earth.