Space Science

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This week over 100 scientists from around the world came to Huntsville, Alabama to talk about magnetic reconnection. What is reconnection and why do they care about it?

Reconnection refers to a particular way that magnetic fields from different sources come together. You know how a magnetic compass points constantly to the north pole? A compass can point vertically as well, if you have one that is designed to do so. If you fly above the north pole the magnet will point down toward the ground. If we fly into space and line up an infinite number of little compasses, nose to tail, then we can visualize this three-dimensional line of magnets as what scientists call a magnetic field line.

Scientists visualize many different shapes built from magnetic field lines: toroids, loops, streamers, complex spirals and even detached bubbles. When different magnetic field lines come near each other, they can get jumbled up, as in a magician's trick where two ropes, say a yellow one and a blue one, are knotted together and then cut, apparently cutting both ropes. But then the magic occurs and the ropes miraculously reappear as whole ropes again. In reconnection, however, the reassembled ropes are mixed: the top of a yellow rope is attached to the bottom of blue rope, and vice versa. This allows, for example, for magnetic field lines from the Sun to connect to magnetic field lines at Earth.

Reconnection is one of the most universal mechanisms that scientists study. It is important, for example, at the surface of the Sun, providing a mechanism for release of enormous quantities of energy. This energy accelerates energetic plasma out into the solar system. (Plasma is a rarefied, electrified gas that is important in space, in the upper atmospheres of planets, and close at home in fluorescent lights.) Reconnection governs how this plasma interacts with Earth's magnetic fields and is implicated in the mechanisms at the core of Earth that generates our own magnetic field. The reconnection of magnetic field lines is also postulated as a mechanism for unusual magnetic topologies at Mars. These topologies range from plasma voids to stretched field lines to free-floating plasma bubbles that can remove some of the already thin Martian atmosphere. Reconnection plays a role in energy loss in the laboratory tokamaks used by nuclear scientists seeking to obtain nuclear fusion. And it is central to understanding distant astrophysical phenomena such as pulsars, magnetars, and enormous jets of very fast plasma jets that stream away from black holes.

In short, reconnection is a hot topic that brings together scientists studying the near-Earth space, the Sun and distant stars.

Scientists measure reconnection from satellites traversing the space about Earth, often flying in close formation (at distance of 10 to 400 km) to more accurately map out the tangled rope knots of the magnetic field lines involved in reconnection. Observations are taken with highly sensitive devices, called magnetometers, that measure the strength and direction of a magnetic field. Measurements are also taken with instruments that measure number and composition of the local plasma populations. In addition to making measurements at the location of satellites, measurements are also made of highly energetic atoms that can be traced back to the interface between the solar plasma and the interstellar medium at the most extreme edges of our solar system. This region is just now being sampled by the two Voyager spacecraft that were launched over thirty years ago. These spacecraft are so far away that it takes about 12 hours for a signal to reach from the spacecraft to Earth.

Space is very large and reconnection takes place in only small regions. There are only a limited number of research satellites in space, so there are never enough observations. Scientists therefore use computer models of the reconnection regions which are then compared with the observations. These models are so complex that they are run on some of the fastest computers in the world, like NASA's Columbia and Oak Ridge's Jaguar supercomputers.

This combination of space measurements and detailed modeling give us new insights into the magical jumbling of magnetic fields known as reconnection.

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