What is Space Plasma?

Plasma is often referred to as the ‘fourth state of matter’, after the solid, liquid and gaseous states. The plasma state is achieved when matter becomes so hot that some or all its constituent atoms are split up into electrons and ions, which can move independently of each other. Because they are made up of electrically charged particles, plasmas are strongly influenced by electromagnetic fields, which can lead to very complex and interesting behaviour.

It is estimated that 99% of matter in the visible universe is in this state; plasmas are found in the solar corona and solar wind, in the magnetospheres of the Earth and other planets, in the tails of comets, in the inter-stellar and inter-galactic media, and in the accretion disks around black holes. Plasmas can also be found on Earth, generated by natural phenomena such as lightning bolts or artificially within nuclear fusion reactors.

In the Space Plasma Physics Group, we study plasmas in the Earth’s magnetosphere and the solar wind, and what happens when they interact. These plasma environments are natural laboratories which offer the unique opportunity to study various plasma properties and processes. 

The Magnetosphere

The Earth has a magnetic field that is generated by electric currents flowing in its liquid outer core. Close to the Earth, this magnetic field looks like that of a bar magnet - a magnetic dipole - and its direction can be detected with a simple compass.

The Earth’s magnetic field extends far into space, where it meets the interplanetary magnetic field, which is carried throughout the solar system by the solar wind, a stream of plasma emanating from the Sun that flows through the solar system at typical speeds of 450km/s. The solar wind is diverted around the Earth’s magnetic field, compressing the side facing the Sun and stretching the side pointing away from the it into a long tail. The region of space containing the Earth’s magnetic field is called the magnetosphere.

All the plasma in the magnetosphere comes from either the ionosphere (a region of the upper atmosphere) or the solar wind, varying in temperature and density throughout the system. Most of the plasma is too tenuous to see with the naked eye or even with a telescope: while the air at sea level has a 100,000,000,000,000,000,000 particles per cubic centimetre and a temperature of 20 ° C, the densest, coldest part of the magnetosphere has between 10 and 10,000 particles per cubic centimetre and a temperature of 58,000 ° C - hotter than the surface of the Sun!  

The Magnetosphere and the Aurora

It is because we have a magnetosphere that our planet has the spectacular aurora borealis and australis - the northern and southern lights that can often be seen at night near the Arctic and Antarctic circles. The aurora is caused by electrons from the magnetosphere being accelerated along the Earth’s magnetic field into the upper atmosphere, where they collide with atmospheric particles at altitudes between 100 and 200km. The brightest colour of aurora, green, is caused by electrons hitting oxygen atoms in the atmosphere.

Images from space have shown us that the aurora forms ovals centred around Earth’s magnetic poles. The radius of these ovals gets larger and the aurora moves to lower latitudes when the Earth’s magnetosphere is strongly affected by the solar wind or engulfed by a coronal mass ejection, a massive eruption of solar plasma and magnetic field that travels through the solar system at speeds much faster than the normal solar wind. 

During the strongest events the auroral oval can reach as far south as the UK. Sign up to aurorawatch to receive alerts when you can see the aurora in the UK!

Space Weather: Effects in space

While the magnetosphere acts as a protective shield, stopping the majority of energetic particles, consequences of the solar wind-magnetosphere interaction can still be felt near Earth. The ensemble of effects this has on our technology and society are referred to as ‘Space Weather’.

The magnetosphere is home to the radiation belts, regions of space filled with highly energetic protons and electrons that can be harmful to astronauts and spacecraft. Radiation belt particles are energised in the hours and days after the magnetosphere has been hit by a coronal mass ejection or exposed to particularly strong solar wind. The orbits of many communications satellites (such as GPS) are located within the outer radiation belt, making them susceptible to space weather effects.

Even though it does a good job of protecting us, the magnetosphere isn’t completely benign. It is home to the dangerous radiation belts, regions of space filled with highly energetic protons and electrons that are harmful to astronauts and can damage spacecraft. The radiation belts are much more dangerous in the hours and days after the magnetosphere has been hit by a coronal mass ejection or exposed to particularly strong solar wind. The orbit of the GPS constellation and Geosynchronous orbit, the location of the vast majority of communications satelites, are both within the outer radiation belt which makes them vulnerable during some space weather events.

Space Weather: Effects on the ground

Space Weather can also affect the Earth’s surface and atmosphere. During space weather events there is a higher than usual flux of charged particles impacting the upper atmosphere. This can subtly change the conditions in the ionosphere and interfere with radio and satellite communications. These increased particle fluxes are strongest at the poles and can result in diversion of transpolar flights.

Power grids can also be impacted by space weather. The interaction between the solar wind and the Earth’s magnetosphere can make the Earth’s magnetic field oscillate. Oscillating magnetic fields in turn generate electric currents, which can then flow within power grids and overload them.

It is only by properly understanding the interaction between the solar wind and the magnetosphere that we can accurately predict and mitigate the effects of space weather on our society.

Resources:

Space Plasma Resources:
Beginners guide to space plasma physics
Public Engagement 

Space Plasma Meetings:
All Meetings
Seminar Series

Head of Space Plasma Physics:
Dr. Daniel Verscharen
+44 1483 204 951
d.verscharen [at] ucl.ac.uk