How much do we really know about Earth’s magnetic field? For that matter, how much do we really understand about any kind of magnetic field, terrestrial or subatomic? This coming March, NASA will be launching the Magnetospheric Multiscale Mission (MMS), an effort ten years in the making which will hopefully answer some of the many outstanding questions we have. In particular, the mission — which consists of four spacecraft that will arrange themselves into a pyramid — will create the first detailed three-dimensional maps of a process known as magnetic reconnection, the phenomenon we experience most directly as geomagnetic storms, solar flares, and even aurora borealis and australis.
The MMS will basically be a souped-up version of the successful Cluster II Mission that was run by the European Space Agency. Rather than launching its four probes in pairs, the MMS vehicles will all launch together as a stack in an Atlas V 421 rocket, in March 2015. As the picture below shows these vehicles push the size limit for the cross section of a craft that can be carried fully assembled in such a rocket. The ATHLETE robot, a separate project planned for some unknown future point in time, uses much the same kind of geometry as the MMS launch concept, even down to the ability to stack multiple vehicles within the rocket core.
The four MMS spacecraft, stacked and ready to go
The four MMS spacecraft, stacked and ready to go
Once they reach their destination — a highly elliptical orbit around Earth — the MMS vehicles will separate, form themselves into a pyramid with one craft at each vertex of the tetrahedron, and then deploy their feelers. Large distances between each craft — up to 250 miles/400 kilometers — will be used for identifying reconnection events, while smaller probe separations, down to just a few kilometers, will be adopted to explore the processes that drive the actual reconnection. The highly elliptical orbit of the formation around Earth will be optimized to spend the most time in places where magnetic reconnection is showcased, namely the day-side magnetopause and the magnetotail.
Read: The Earth and Moon, as seen from elsewhere in the universe
The magnetopause is where pressure from the solar wind and the planet’s magnetic field are equal, while the magnetotail extends great distances away from the originating planet as pressure from the solar wind acts on the magnetosphere. Magnetic reconnection occurs in thin layers just a few miles thick where magnetic and mechanical energy are concentrated. Understanding reconnection is important for our efforts to create fusion because it is one of the main mechanisms that foils the magnetic confinement of the material to be fused.
If asked about how the Earth’s magnetic field developed (and continues to develop), many experts would point to its iron core and mumble something out electric currents and dynamos. The truth is our best simulations can not yet explain many of the features that are observed. While the temperature of our planet’s core is hot (as hot as the surface of the Sun, which incidentally puts it well above the Curie temperature where magnetization can be sustained) we are pretty certain the core is solid as a result of the great pressure it is under. At the other extreme in size — the small scale world of theoretical point charges and individual electron spins — descriptions of magnetic phenomena can be equally difficult to pin down.
In simplified situations at least, the seemingly concrete magnetic field can be reduced to nothing more than the result of combining electrostatics with special relativity. The main aspects of special relativity that are important here — namely that measurements of space and time depend on a frame of reference — are not introduced just to try to make this article appear smart. They are in fact fundamental to understanding how magnetic forces arise. We won’t dwell on this issue other than to say that the small attractive force that develops between two parallel currents in two wires, for example, is understood to result from the relativistic contraction of space that is associated to the moving charges. If the actual space between the wires is experienced to be smaller, some force must account for the state of affairs. In other words, the magnetic field is a mathematical convenience we use only in interpreting different vantage points of the mother electromagnetic field.
Popping back out to bigger scales, one curious observation is that in contrast to most familiar planets, our neighbor Venus does not internally generate a magnetic field. Somewhat surprisingly, evidence was recently found that there is magnetic reconnection in the induced magnetotail of Venus. The so-called “microphysics” of recombination includes energetic particle acceleration, astrophysical plasmas and turbulence — all complex events we hope to appreciate more about once the MMS probes begin to do their thing.
TAGS: Science,Space,Space Exploration,Nasa,EarthGeomagnetic,StormMagnetic .
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