Aerospace Scientists Contribute to Breakthrough Research
Imagine a busy freeway with lanes of traffic moving in opposite directions. What would happen if the center divider were suddenly removed and the middle lanes were merged?
That’s one way to envision the explosive energy release in the phenomenon known as magnetic reconnection, in which adjacent magnetic fields directed opposite to each other suddenly collide and annihilate one another, transferring energy to the surrounding plasma environment. Plasma, sometimes called the fourth state of matter, is a gas composed of charged particles, usually positive ions and (negative) electrons. Due to these charges, plasmas exhibit behavior that neutral gases do not, including intricate interactions with electric and magnetic fields.
Aerospace scientists recently contributed to a breakthrough discovery in the field, and the research is featured in Science magazine, one of the most prestigious journals serving the scientific community. The research program at Aerospace is led by Dr. J. Bernard Blake, Dr. Joseph Fennell, and Dr. James Clemmons of the Space Science Applications Laboratory, who are the Aerospace contributors to the Sciencearticle, along with Dr. Drew Turner, of the Space Sciences Department.
The magnetic reconnection phenomenon is believed to be universal, occurring near stars, black holes, and other astronomical bodies. The effects of reconnection can be clearly seen in the form of coronal mass ejections on the sun and shimmering auroras on Earth — but the underlying mechanism, the microscopic physics at the heart of the reconnection process, has not been well understood.
In 2015, NASA launched the Magnetospheric Multiscale (MMS) mission to study reconnection in Earth’s magnetosphere, which serves as a conveniently active and accessible natural laboratory for space-plasma physicists. The four identical MMS spacecraft are carrying a number of specialized sensors, including several instruments designed and built by the Space Science Applications Laboratory at Aerospace. These instruments, known as the Fly’s Eye Electron Proton Spectrometers (FEEPS), have been characterizing the energetic charged particles that are produced from the breakup and reconnection of magnetic fields. These particles — mostly electrons and protons — can increase the intensity of radiation in the space environment, posing a hazard to spacecraft and astronauts alike.
As Turner explains, the MMS spacecraft each carry two FEEPS instruments, each of which contains 12 silicon “eyes” for detecting electrons and protons of varying energy levels. The spacecraft fly in a pyramidal formation that allows them to straddle the thin boundary of the magnetic bubble surrounding Earth (the magnetopause) and make simultaneous, coordinated measurements of local plasmas and fields.
The formation is exceptionally tight: at one point, the satellites maintained a separation of only six miles. This level of precision is critical for the mission, Turner says. “The MMS results are unprecedented due to the tight formation of the four identical observatories and level of resolution available from the instruments. They allow us to observe physical mechanisms acting on smaller scales than ever previously observable — those on the electron kinetic scale, or tens of kilometers in space,” he says.
Plasma researchers need to consider dynamic interactions on several scales, from the large, measured in Earth radii, to the smaller electron kinetic scale, defined by the circular range of motion for an electron in a constant magnetic field — roughly 10 kilometers in this plasma environment.
The MMS mission has initially been focusing on the sun-facing side of Earth’s magnetosphere, which is predominantly shaped by the solar wind and related solar activity. In this region, magnetic fields from the sun can directly link with those surrounding Earth. A later phase of the mission will examine the night side, where reconnection also occurs within purely magnetospheric fields (i.e., those from Earth).
After months of reviewing data, the science team recently confirmed that the MMS satellites made several encounters with reconnection sites, where they observed the conversion of magnetic energy into particle kinetic energy. They also measured the intense current and electric field that causes the dissipation of magnetic energy and identified crescent-shaped electron distributions that carry the current as a result of demagnetization and acceleration. The FEEPS instruments in particular provided key observations of the change in magnetic topology by using electrons as tracers of the magnetic field.
Turner says these encounters have yielded important new insights into the microphysics underlying the reconnection of the interplanetary and terrestrial magnetic fields. For example, the persistence of the characteristic crescent shape in the electron distributions suggests that the kinetic processes causing reconnection of magnetic field lines are dominated by electron dynamics, which produce the electric fields and currents that dissipate magnetic energy.
The MMS observations confirm what some models had suggested, but they also have provided new results that have not been captured in any models or simulations to date. “The mission is most definitely producing unexpected new insights, about not only reconnection, but other magnetospheric and solar-wind processes as well,” Turner says. “The mission is giving us a much keener appreciation for the importance of processes at the electron scale and how those microscopic, local processes can then have effects on the entire system.”
The success of FEEPS is all the more satisfying, considering its lengthy development — the project was originally proposed in 2005, and the first instruments were delivered to NASA in 2012. During that time, a dedicated team of engineers and technicians from the Space Instrumentation Department and ETG designed, built, and tested the instruments. The team also took part in the initial commissioning, tuning, and operations by means of a ground station located within the Aerospace laboratories.