The cusp region of the magnetosphere is special because it acts as a funnel, focusing particles and waves down to a small region. We know that when reconnection occurs, we can see energized particles come down into the atmosphere. And, depending on how they travel, the particles map to different regions in the magnetosphere. This means TRACERS can help us study vast areas of near-Earth space by orbiting through one small area, the cusp.

One of the most important aspects of the TRACERS mission is that it includes two satellites orbiting in tandem, allowing for multiple 'snapshots' of the funnel-shaped cusp very close to one another that researchers can use for comparison. This is crucial because much of the science done in this area of space physics has relied on measurements taken by one spacecraft at a time. So, while past research has been very helpful in identifying that magnetic reconnection does occur, there are long-standing questions remaining about the process, including: Does reconnection turn off and on in time, does it happen in multiple places at the same time, or something else? TRACERS will allow us to fill in these and other related questions.

Over the years, researchers have also used sounding rockets to study the cusp. TRICE-II was in many ways the proof of concept for TRACERS. Two rockets, both with similar instruments as TRACERS, were sent into the cusp at about the same separation that the two TRACERS satellites will follow (10-120 seconds). While TRICE-II provided promising data, this was just one trip into the cusp. The two TRACERS spacecraft will follow a relatively low orbit (~550km) that will take the two satellites through the cusp region a few times each day, more than 3,000 times in the first year! Since previous related studies relied on data from just one trip into the cusp or one satellite in orbit, TRACERS will be unique in that it will provide much more data under a range of geophysical conditions than has yet been possible.