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horizon lecture

The most powerful explosions in space may not be what you think they are

Magnetized plasma in outer space carries huge amounts of energy that occasionally gets released, typically in the form magnetically driven explosions. Such magnetic explosions are what produce solar flares on the Sun as powerful as a billion atomic bombs and magnetar flares that release more energy than even the largest supernova explosions. In the Earth atmosphere, they fuel magnetic storms and auroras. And in fusion reactors they are dreaded as the source of catastrophic failure.

MMS mission, NASA
Artist rendition of MMS spacecraft (NASA)

But how do they work? The physical process behind them is “magnetic reconnection”, which until recently was a big mystery. Even though magnetic reconnection has far-ranging effects on very large spatial scales, the critical processes take place on very small spatial scales. Intricate interactions between charged particles and electromagnetic fields in the so-called diffusion zone is what makes magnetic reconnection happen. In the laboratory, this zone is way too small to fit probes into. In the Earth environment, it is typically smaller than 100km, while the overall system may be as large as a 100 thousand km or even larger. So how do we find and get measurements from inside this zone? 

Taking on this challenge is exactly the purpose of the $1B Magnetospheric Multiscale Mission (MMS) launched by NASA in 2015. Four spacecraft flying in a tight formation (as close as 10km apart) have been searching for diffusion regions in the Earth magnetosphere to take high precision measurements inside them – successfully! They have found some and made the crucial measurements that have now determined without doubt the physics of the diffusion region. The lecture will present the many amazing consequences of magnetic reconnection throughout the universe and give a brief explanation of the theoretical predictions of how magnetic reconnection works. Then, the MMS mission will be introduced, followed by a description of the decisive measurements, which resolved this scientific puzzle.