Magnetic Reconnection & Why it Matters to You

Recently, NASA launched the Magnetospheric Multiscale (MMS) mission to detect a phenomenon known as magnetic reconnection. Unless you have taken a course in space physics, chances are you have not run across the concept. However, magnetic reconnection plays a key role here on Earth as well as throughout the universe. To understand why NASA wants to learn more about reconnection, we’ll start off with a few basics.

All magnetic fields are dipoles, that is, they have two poles, north and south. The flow of the magnetic field runs from the North Pole to the South Pole. The Earth itself acts like a giant bar magnet. The Earth’s magnetic North Pole lies near the geographic South Pole and vise versa. Hence, geographically, the flow of Earth’s magnetic field runs from south to north as seen below:

Courtesy: NASA

Three things to consider regarding electric and magnetic fields:

A changing magnetic field creates an electric field.

An electric current creates a magnetic field.

A particle with an electric charge will travel along the path of a magnetic field line.

Space itself consists mostly of particles with an electric charge called plasma. The intense heat of the Sun separates the atomic bonds between electrons (negative charge) and the nucleus that has protons (positive charge). Thus, normally electrically neutral atoms are broken apart and spread throughout the Solar System as an electrified gas (plasma) via the solar wind.

The Sun’s magnetic field is embedded in the solar wind and expands past the most distant planets. This magnetic field is thus known as the Interplanetary Magnetic Field or IMF. As this plasma travels out into the Solar System, some of it will encounter the Earth’s magnetic field on the day side. This is one of two areas where reconnection occurs around Earth.

Reconnection is when the IMF field lines merge with the Earth’s magnetic field lines to transfer mass and energy from the solar wind into Earth’s magnetic field. The possibility of reconnection is most strong when the IMF and Earth’s magnetic field lines flow is opposite of one another. Remember that Earth’s magnetic field flows from the geographic South Pole to North Pole. Thus, reconnection occurs most often when the IMF is flowing southward.

In physics, the letter B signifies a magnetic field. A three dimensional coordinate field is signified by the letters x, y, and z. The z-axis is up and down with negative z values running southward. When the IMF has a strong negative Bz direction, this means the IMF is flowing opposite of the northward flow of the Earth’s magnetic field and the potential for reconnection is high.

So why does any of this matter to us? When reconnection occurs the probability for magnetic storms on Earth is high. These storms create the aurora, which is the most aesthetic feature of these events. The plasma from the IMF is transferred to the Earth’s magnetic field during reconnection and follows the solar wind over to the night side.  Here, reconnection occurs a second time as the Earth’s magnetic field is stretched out by the solar wind.  Opposing magnetic field lines reconnect and unleash plasma at a high velocity.  The process is diagrammed below:


Courtesy: NASA

The unleashed plasma then follows the Earth’s magnetic field lines into the Polar Regions. Unabated, the kinetic energy of these particles would be harmful to life. However, oxygen and nitrogen atoms in the upper atmosphere absorb the kinetic energy lifting their electrons to a higher energy orbit. When the electrons recede back to a lower energy orbit, the harmful kinetic energy is converted into harmless light radiation resulting in the aurora at the Polar Regions.  The aurora as seen from the International Space Station is below:

The story does not end there. As mentioned above, a changing magnetic field produces electric currents. Reconnection causes disturbances in the Earth’s magnetic field that can induce electric currents in both orbiting satellites and ground based power grids. These currents can cause expensive damage to electrical systems. A better understanding of the process of reconnection can provide more accurate forecasts of magnetic storms. These forecasts can inform satellite operators when to go into protective shutdown mode to prevent damage and allow power grids to take preventative action against blackouts.

The potential for damage is not insignificant. The 1989 magnetic storm caused a blackout across Quebec for nine hours. During that event, auroras were seen as far south as the Gulf Coast. The Carrington event of 1859 was much stronger than the 1989 storm. The electrical currents induced by this magnetic storm were so strong that telegraphs were able to operate even when disconnected from their batteries. A similar event today would, of course, result in much more significant damage given how much more reliant we are on electronics than in 1859. This is the most pressing reason NASA wants to understand the nature of reconnection. There are many other astrophysical applications as well.

The MMS Senior Project Scientist Tom Moore describes how the mission will research magnetic reconnection below:

The MMS mission will cost $850 million.  To put that in perspective, it cost $1.6 billion to build MetLife Stadium and $1.3 billion for the luxury high rise at 432 Park Avenue.  Space is not cheap, but not more expensive than major construction projects back here on Earth.

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