A few hours ago the four MMS (Magnetospheric Multiscale Mission) spacecraft were launched atop an Atlas V 421 rocket from Cape Canaveral. After nearly two hours the spacecraft started separating from the rocket’s last stage, one at a time at intervals of about five minutes. It’s only the beginning of a complex phase of tests, deployment of their booms with the sensors, and positioning of the probes in a tetrahedron configuration which will last more than five months.

The MMS mission is really ambitious because it’s based on the work of a constellation of four identical spacecraft that will operate together in a tetrahedral formation in order to make three-dimensional measurements. The purpose is to study the magnetosphere in a way more sophisticated than those previously attempted.

In particular, the space probes will study the phenomenon of magnetic reconnection. It’s a process in highly conductive plasma in which the magnetic topology is rearranged and the magnetic energy is converted into kinetic and thermal energy and into particle acceleration.

This process takes place in many parts of the cosmos: the stars’ atmosphere, near black holes and neutron stars, and the border between the solar system’s heliosphere and interstellar space. The MMS space probes will observe the phenomenon in the vicinity of the Earth to understand it more generally.

Magnetic reconnection causes various effects on the Sun and the Earth. The most obvious ones are the coronal mass ejections from the Sun and auroras on Earth. It’s therefore a phenomenon not only interesting from a scientific point of view but one that also has consequences on the planet. Solar storms have a potential increasingly dangerous considering that there are more and more orbiting satellites and the power grids on the surface are more and more complex.

The study of magnetic reconnection is also important in the research on controlled nuclear fusion. That’s because this phenomenon is what prevents the magnetic confinement in the material used in the fusion. The consequence is that a better understanding of it could allow making progress in this research.

It’s for these reasons that NASA invested about $1.1 billion in the MMS mission. Our current knowledge on magnetic reconnection derives mainly from theoretical studies, computer models, and observations of events seen on the Sun. The big problem is that our current knowledge is approximate.

The four MMS space probes will allow obtaining direct measurements of this phenomenon taken in what was called a space laboratory. In fact, they’re going to travel in the Earth’s magnetosphere, which is an environment filled with plasma. It’s a perfect environment to discover the secrets of magnetic reconnection.

The MMS space probes will use their 11 instruments with a total of 25 sensors to measure the speed of the charged particles, the movement of plasma, and electromagnetic fields with levels of accuracy never achieved before. Throughout their two-year primary mission, they’ll fly in a highly elliptical orbit that will vary over time. The distance between the probes will change over time as well, with a minimum of 10 km between them.