A PASSION FOR SPACE
The reason why the solar wind moves so incredibly fast mauy be on the verge of finally being explained
Two decades ago I first started thinking about what science could be done with a spacecraft orbiting close to the Sun. We only have the chance to study one star with any degree of intimacy, and it’s the one at the centre of our very own Solar System.
Of course, I wasn’t the first to ponder this. A report written by the Simpson Committee of America’s National Academy of Science in 1958, at the very start of the Space Age, recommended “a solar probe to pass inside the orbit of Mercury to study the particles and fields in the vicinity of the Sun”. This feat was eventually achieved by the Helios 2 spacecraft in the mid-1970s, and extremely valuable data was collected.
The spacecraft made measurements of the so-called solar wind, which is a gusty stream of particles and magnetic fields generated by the Sun’s million-degree atmosphere. An atmosphere this hot has such a high pressure that it cannot be fully restrained by the Sun’s gravitational pull and the top layer escapes into space.
What’s puzzling, though, is the fact that the solar wind moves at much higher speeds than expected. There must be some physical processes that provide the wind with an additional acceleration. The question is, what are these processes? The Helios 1 and 2 spacecraft helped pose this question, but were not able to answer it. For this, different observations are needed and luckily for scientists like me they are just around the corner. The hot questions Solar Orbiter, the mission to provide answers to these long-standing questions, is a European Space Agency spacecraft with strong NASA involvement that’s in the final stages of its build at the moment. I was lucky enough to visit the spacecraft at Airbus in Stevenage while the final instruments were being added and the first remote communications tests began. You can see what I got up to in the August episode of The Sky at Night (which will still be available on BBC iPlayer for a couple of weeks after this issue goes on sale).
Solar Orbiter has been specifically designed to answer science questions posed by myself and other scientists; questions that can only be answered by getting up close to the Sun and studying it with cameras that both image the surface and atmosphere, and that sense the particles and fields around the spacecraft.
Through the solar wind, solar ejections and high-energy particles, the Sun creates and controls an enormous bubble that is effectively its extended atmosphere – the heliosphere. Living on a planet in this atmosphere, we can see the space weather this creates on Earth. The solar wind also strips the atmosphere from Mars and creates aurora in the skies of planets that have magnetic fields, like Earth, Jupiter and Saturn.
Due for launch in early 2020, Solar Orbiter will allow us to study solar emissions in detail and, crucially, look back to where they originated from for the first time. Combined with data collected by NASA’s Parker Solar Probe, my decadesold dream may finally be realised.