The four identical spacecraft of NASA’s Magnetospheric Multiscale, or MMS, mission (one of which is illustrated here) fly through the boundaries of Earth’s magnetic field to study an explosive process of magnetic reconnection. Thought to be the driver behind everything from solar flares to aurora, magnetic reconnection creates a sudden reconfiguration of magnetic fields, releasing huge amounts of energy in the process. Credit: NASA’s Goddard Space Flight Center
Just under four months into the science phase of the mission, NASA’s Magnetospheric Multiscale, or MMS, is delivering promising early results on magnetic reconnection—a magnetic explosion that’s related to everything from the northern lights to solar flares. It will help us to better understand what drives magnetic reconnection events which send particles at near the speed of light and create oscillations in Earth’s magnetic fields, affecting technology in space and interfering with radio communications.
Planned for more than 10 years, the MMS mission started with the launch of 4 ientical spacecraft on a single rocket in March 2015. 9 months later, the spacecraft are flying through the boundaries of Earth’s magnetic system, the magnetosphere. Their initial orbit is taking them through the dayside boundaries of the magnetosphere—magnetopause—where the solar wind and other solar events drive magnetic reconnection. Eventually, their orbit will loop out farther to carry them through the farthest reaches of the magnetosphere on the night side, where magnetic reconnection is thought to be driven by the build-up of stored energy.
“We’ve recorded over 2,000 magnetopause crossings since our science phase began,” said Jim Burch. “In that time, we’ve flown through hundreds of promising events.” One of the key features of MMS is its scaling ability. The 4 spacecraft fly in a tetrahedron, to give 3D views. Because the four spacecraft are controlled independently, the scale of their formation and images can be zoomed in or out by a factor of 10.
“We can see the effects of reconnection on the sun in the form of coronal mass ejections and solar flares,” said Michael Hesse. “But with MMS, we’re finally able to observe the process of magnetic reconnection directly.” Magnetic reconnection is a when magnetic fields reconfigure suddenly, releasing huge amounts of energy. When magnetic field lines snap and join back together in new formations, some of the energy that was stored in the magnetic field is converted to particle energy in the forms of heat and kinetic energy. “It impacts both the temperature and speed of particles in a plasma, two of the defining characteristics.”
The explosive realignment of magnetic fields — known as magnetic reconnection — is a thought to be a common process at the boundaries of Earth’s magnetic bubble. Magnetic reconnection can connect Earth’s magnetic field to the interplanetary magnetic field carried by the solar wind or coronal mass ejections. NASA’s Magnetospheric Multiscale, or MMS, mission studies magnetic reconnection by flying through the boundaries of Earth’s magnetic field. Credit: NASA Goddard/SWRC/CCMC/SWMF
A suite of 6 instruments characterize the behavior of electric and magnetic fields at magnetic reconnection sites: FIELDS suite, duplicated on each of the 4 MMS spacecraft, which contain 6 sensors that work together to form a 3D picture of the electric and magnetic fields near the spacecraft. This suite has a very high accuracy, in part due to the very long booms on each sensor. The long booms allow us to measure the fields with minimal contamination from the electronics aboard the spacecraft. FIELDS observations looks for one of the smoking guns of magnetic reconnection, ie parallel electric field.
“What we’re looking for is an alignment of electric and magnetic fields,” said Goodrich.
In the simplest view of plasma—known as ideal plasma—the charged particles spinning along magnetic field lines carry enough current to instantaneously short out any electric field parallel to the magnetic field. But in actuality, plasma doesn’t ever behave quite that simply, so scientists must consider a more detailed, complex version of the physics to understand how and why reconnection is able to occur. These non-ideal plasmas—open up the possibility for the creation of gaps in these zooming charged particles, allowing parallel electric fields to form for an observable length of time. “These events would have to combine energy dissipation, particle acceleration, and sudden changes in magnetic topology,” said Goodrich.
FIELDS suite can spot examples of parallel electric fields at time scales down to half a second. here are also 2 other particle detectors aboard MMS: Fly’s Eye Energetic Particle Sensor, or FEEPS, and the Energetic Ion Spectrometer. The measurements are providing evidence for a mechanism by which particles can escape the Earth system and join the interplanetary medium.
When magnetic reconnection happens on the day-side, magnetic field lines from the sun connect directly to Earth’s magnetic field. “The linking of these magnetic fields means that particles can drift from within the magnetosphere to the boundary between Earth’s magnetic field and the solar wind,” said Cohen. “Once they get to that boundary, further reconnection events allow them to escape and float along the interplanetary magnetic field.”
This magnetic sun-Earth connection also means that particles disrupted by magnetic reconnection spiral along these newly linked magnetic field lines toward Earth, allowing evidence of magnetic reconnection to be seen even from tens of thousands of miles away.
MMS observations can clearly able to distinguish between the directions the particles are moving, which will help scientists better understand what mechanisms drive magnetic reconnection.”Now we’re sifting through those observations and we’re going to be able to understand the drivers behind magnetic reconnection in a way never before possible.”
http://www.nasa.gov/feature/goddard/nasa-s-mms-delivers-promising-initial-results
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