The MMS mission, marking a year in space, described for the first time what happens at the meeting between the Earth's magnetic field and the Sun's magnetic field
Like storm researchers sending sensors into the heart of a hurricane, so NASA flew four spacecraft through an invisible vortex in space, called 'magnetic reconnection' or 'magnetic reconnection'. Magnetic refusion is one of the driving forces behind radiation in space, and is therefore a key factor in studying our space environment, among other things so that we can protect the spacecraft and astronauts sent into space.
In the first important results of MMS - NASA's Magnetospheric Multiscale mission - there is a first look at the interaction between the Earth's magnetic field and that of the Sun. They are presented in an article published these very days (13.5.2016) in the prestigious scientific journal Science. The paper describes the first direct and detailed observation of magnetic refusion, which occurs when two opposing magnetic field lines break and reattach to each other, releasing enormous amounts of energy. The research shows that magnetic reconnection is controlled by electron physics, thus providing vital information about this fundamental process in nature. The study was conducted by physicists from the University of Maryland.
Although space is a better vacuum than any vacuum that can be created on Earth, it still contains particles and is bustling with activity - it has a complex system of magnetic fields and energy. Most people don't give much thought to the Earth's magnetic field even though it is as necessary to our lives as air, water and sunlight. The magnetic field provides an invisible but essential barrier that protects Earth from the 'solar wind': gusts of charged particles that the Sun's magnetic field blasts out from the Sun's outer layers.
The interaction between these two magnetic fields - the Earth's and the Sun's - can produce storms in space near the Earth, which have the power to disable satellites and lead to many problems here on Earth, despite the lines of defense offered by the Earth's magnetic field. Sometimes, when two arrays of magnetic fields connect, an explosive reaction occurs: when the magnetic fields realign and lock in their new array - they send out jets of particles and energy.
The effects of this sudden release of particles and energy – such as giant solar flares, auroras, radiation storms in near-Earth space, high-energy cosmic particles coming from other galaxies – have all been observed across the Solar System and beyond. But we have never directly witnessed the phenomenon of magnetic refusion. Satellites did notice the particles that accelerate quickly, but not the driving factor itself - just like seeing all the fragments and debris that fly due to a hurricane, but not seeing the storm itself.
"The mission we developed gives us, for the first time, the precision necessary to collect observations from the heart of magnetic fusion," said Jim Burch, principal investigator of the MMS mission at the Southwest Research Institute in San Antonio, Texas and first author of the paper. "We got results faster than we could have expected. When we saw magnetic fusion in action, we saw one of the fundamental forces of nature."
MMS consists of four identical spacecraft that were launched in March 2015. They fly 10 kilometers apart at the edge of the Earth's magnetic field in a pyramid formation - so that they can create a complete 16D map of all the phenomena they encounter. On October 2015, 25, the MMS array passed directly through a magnetic reconnection event at the boundary where the Earth's magnetic field collides with the Sun's magnetic field. Within seconds, 30 sensors on each of the spacecraft collected thousands of observations. The spacecraft array provides imaging of the electrons inside the pyramid once every 100 milliseconds. The amazing level of detail in the data makes it possible to see things that were previously blurry, because the images obtained before the MMS mission were at a time interval of three seconds - a rate XNUMX times slower, and using them to see recombination was impossible.
This unprecedented rate allowed scientists to monitor better than ever the changes in the magnetic and electric fields and also the changes in the speeds and direction of the various charged particles. Just examining the re-fusion phenomenon in detail is an important milestone. But the main goal of the MMS mission is to determine how quickly the magnetic field lines break - which allows the refusion and subsequent energy release to occur. Measuring the behavior of the electrons in the fusion event will make it possible to describe a more accurate description of the process in which it is carried out, and in particular it will be possible to check whether it takes place in a clean and orderly process or in a turbulent vortex of energy and particles.
It turns out that the science behind reunification is simple basic electromagnetism, which is one of the fundamental forces in the universe similar to gravity on Earth. You can see a series of lines in each set of magnetic fields. These field lines are always anchored to some body - a planet, a star - and create a huge magnetic network that surrounds it. Magnetic reconnection occurs very close to the boundary between two such networks.
Imagine rows of magnetic field lines moving opposite each other at such a boundary (MMS spacecraft, for example, move at the boundary where the Earth's magnetic fields meet those of the Sun). Sometimes the directions of the field lines are the same and do not have much effect on each other, like two streams of water flowing side by side. But in a situation where the directions of the field lines in the two groups are opposite, the process of their rearrangement can be dramatic to the point of explosion - particles break out at a speed close to the speed of light. But on the other hand - the process can also be slow and steady.
"One of the mysteries of magnetic refusion is why it's a reaction that's explosive in some cases and stable in others, and in some cases it doesn't happen at all," said Tom Moore, mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. In any case - in an explosive process as well as in a stable process - a huge amount of energy is released and the local particles are thrown far away and cross magnetic boundaries that could not pass in other situations. At the edges of Earth's magnetosphere, such events allow solar radiation to enter space close to Earth.
"From measurements made by previous satellites we know that the magnetic fields behave like a 'rogateka', a slingshot - sending the accelerating protons out," said Berch. "A decades-old mystery is what the electrons do and what connection is formed between the two magnetic fields. Previous measurements of electrons were 100 times slower – too slow to sample the magnetic reconnection region.”
The MMS array checks what happens to the electrons during fusion. When the four spacecraft crossed the magnetospheric boundary on that day in October 2015, they passed directly through the so-called 'dissipation zone', where magnetic reconnection took place. The observations were able to follow the sudden shifts of the magnetic fields and also the moving away particles.
The electrons are shot from the original event in straight lines at a speed of hundreds of kilometers per second and manage to cross the magnetic boundaries that normally deflect them. After crossing the boundary, the particle jets encounter the new magnetic fields, their trajectory curves in response to this and they make a U-turn. These observations are consistent with the 'crescent model' computer simulation, so called because of the characteristic crescent shapes the graphs show - representing the distance the electrons travel across the magnetic boundary before spinning again.
Another surprising result found is that the moment a connection was made between the magnetic field lines of the sun and the earth, the crescents suddenly turned, so that the electrons flowed along the field lines. By observing the paths of these electrons, the MMS array was able to observe for the first time the breaking and merging of magnetic fields in space.
"The data show that magnetic reconnection is a fairly orderly and elegant process," said Michael Hesse, a space scientist at Goddard and the first to develop the crescent model. "There doesn't seem to be much turbulence, or at least not enough to disrupt or complicate the process." The characteristic crescent shape of the electron scatter suggests that understanding how magnetic field lines accelerate particles lies in electron physics.
"The electrons move so that electric fields are created, and these electric fields in turn produce a burst of magnetic energy conversion," said Roy Torbert, a scientist at the Space Science Center at the University of New Hampshire in Durham and one of the authors of the paper. "The collision that our instruments were able to measure provided us with a clear picture of energy release during explosive refusion and the role that electron physics has in the process."
So far, the MMS array has flown more than 4,000 flights through the boundaries of the Earth's magnetosphere, each time collecting information about how the magnetic fields and particles within them move. After the first direct observation of magnetic refusion, the four spacecraft passed through such a fundamental event five more times and provided more information about the process.
A clearer picture of the physics of refusion will also move us one step closer to understanding space weather, including whether solar flares and magnetic storms follow some predictable pattern, like the weather here on Earth. Refusion can also help scientists understand other more energetic astrophysical phenomena such as magnetars, which are neutron stars with an unusually strong magnetic field.
"Understanding recombination is relevant to a whole range of scientific questions in solar physics and astrophysics," said Mark Swisdak, a research scientist at the University of Maryland's Institute for Electronics and Applied Physics. "Refusion in the Earth's magnetic field is relatively low energy, but we can get a good sense of what will happen if we extrapolate to more energetic systems. The edge of the Earth's magnetic field is an excellent test laboratory, because it is the only place where we can fly a spacecraft directly through an area where fusion is occurring."
To date, the MMS mission has focused only on the sun-facing side of Earth's magnetic field. In the future, the array of spacecraft should fly to the other side to study the tail of the magnetic field – which has the shape of a teardrop – facing away from the Sun.
As the mission continues, the team can adjust the structure in which the spacecraft fly - bringing them closer together, thus providing a better observation of the electron paths, or moving them further apart, thus allowing better observations of the proton paths. Each set of observations contributes to explaining different aspects of magnetic reconnection. Such information will help scientists map the details of our space environment - essential information if planning a journey far beyond our planet.
To the announcement of the researchers on the website of the University of Maryland
