EXACTLY WHERE THE PHYSICS IS HAPPENING

The keen observation of the night sky has long been a recognised part of Swedish scientific life, now we’re closer than ever to understanding it.

From the earliest days, the night sky — particularly the colourful aurora borealis — seen prominently over northern Scandinavia, has sparked curiosity.

Over time, this curiosity sharpened into scientific fact-based research. The naked eye was soon assisted by ground-based observations from magnetometers, all-sky cameras, and radars. In time, first sounding rockets and then satellites were launched to further investigate in situ the physical mechanisms behind the aurora, such as acceleration of auroral particles, needed to create the intense auroral displays, and the mechanisms driving the aurora.

Scientists at KTH have long played an internationally key role in the studies of the aurora and the auroral particle acceleration. Both Göran Marklund, professor of Space Plasma Physics at KTH and Per-Arne Lindqvist, research scientist in the same field, have studied the aurora and the mechanisms behind it since the late1970s.

“We often call our research ‘auroral research’. But the aurora is not the result of processes confined only to the Earth’s ionosphere where it is observed, but the result of a long chain of interaction processes between the Sun and the Earth’s magnetosphere. As the continuously emitted, highly variable solar wind hits the Earth’s magnetosphere, a process named reconnection will transfer energy and momentum between particles and magnetic fields. To further understand this process, in situ measurements by satellites crossing the magnetosphere’s outer boundary are needed.” Says Lindqvist as the two scientists explain their role in the continued study of an ever more vital area of space physics.

Electromagnetic hydrodynamic waves (or magneto-hydrodynamic waves) play an important role in the above mentioned processes behind the aurora. They were first described in 1942 by former KTH professor, Hannes Alfvén (1908 – 1995). As an electrical engineer and plasma physicist he had long promoted his theories on electromagnetic hydrodynamic waves and although at first not universally accepted, his theories were soon fully recognised and now these waves are commonly referred to as ‘Alfvén waves’. It is his pioneering work, recognised with a Nobel Prize for Physics in 1970, that has continued in earnest at KTH.

The success of the launch of Sweden’s first satellite VIKING in 1986, and its achievements as the first satellite to explore plasma processes in the Earth’s magnetosphere and ionosphere led not only to successive satellites FREJA and ASTRID-2 and their further investigations, but also to a recognition from the international community that Sweden had a serious research capability and a frontier position in the field.

“We showed the world that we were capable of designing and building advanced rocket and satellite experiments which worked.” Says Marklund. Confidence had grown internationally in the ability of Swedish space science, and engineers, to not only execute exacting experiments but also to build highly precise electric field instruments.

So when scientists at KTH learnt that NASA was getting a team together for a space physics project which would involve four satellites to launch in 2015, the KTH team worked hard on their contribution to a project close to their heart. The Magneto-spheric Multi-Scale (MMS) mission was targeted to deepen our understanding of the process of reconnection operating between the solar wind and many of the planets, including Earth. Magnetic reconnection, transferring energy and momentum between particles and magnetic fields, is a well-known process also in fusion plasmas, solar flares and probably also in astrophysical plasma jets.

A key parameter in this process is the electric field. The world-leading position of the KTH group in measuring electric fields was the reason for being invited to provide the spin-plane double probe electric field experiments on the four MMS spacecraft. So it was that on 13 March 2015, after 10 years of hard work on a 1-billion dollar NASA mission, an Atlas V 421 rocket entered space carrying their instruments. All three components of the electric field in the earth’s magnetosphere are now being measured with the highest resolution possible and frontier science is already being explored. As a result of this large scientific effort, “close to 400 papers have been published in international journals with many authors to each paper.” Says Lindqvist.

So what’s next for Space Physics at KTH? We discussed several new projects including one which Marklund and Lindqvist acknowledge will probably not be complete until after they have retired.

“We are moving away from the earth’s magnetosphere to explore other regions.” Explains Lindqvist. “One project, which we are involved in, and which is already on its way to be launched, is BepiColombo. It will go to Mercury, carrying an electric field instrument we have built. There will be two spacecraft, one will observe the planet and the other is a magnetospheric orbiter which will measure the electric fields, in situ around the planet Mercury, for the first time ever.”

Almost by way of further explanation, and especially to clarify the importance of the study of in situ space physics, Marklund explains. “Astronomers are forced to rely only on the light in different wavelengths emitted from stars, however, our in situ measurements are from exactly where the physics is happening, where there are electric fields, particles and currents, that is a real contrast between us and the astronomers.”