Why study space weather? 

The solar wind, a stream of charged particles from the Sun that carries the Sun's magnetic field with it, interacts with Earth’s magnetic field, causing “space weather”.

When a solar flare (coronal mass ejection or CME) sends charged particles from the Sun to Earth, some of those charged particles interact with the local plasma within the Earth's magnetosphere. This cascading transfer of energy causes things like the northern and southern lights (auroras). Sometimes, especially due to larger CMEs, these events cause problems with our electrical infrastructure. 

There is evidence of CMEs in the past that would be catastrophic to our current communications and guidance systems. A major reason NASA and the University of Iowa aim to better understand the physical processes that underlie space weather is to protect humanity from such events in the future. 

How will TRACERS help us understand the physics behind space weather? 

First, the instruments chosen for this mission allow us to study the local plasma involved in magnetospheric reconnection. The instruments' measurements 'diagnose' the plasma in terms of particles (electrons and ions), electric and magnetic fields, and electric and magnetic waves.

• ACE: Analyzer for Cusp Electrons
• ACI: Analyzer for Cusp Ions
• EFI: Electric Field Instrument
• MAG: Fluxgate Magnetometer
• MSC: Magnetic Search Coil
• MAGIC: MAGnetometers for Innovation and Capability

The cusp region of the magnetosphere is special because it acts as a sort-of 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 focusing on one small area, the cusp.

One of the most important aspects of the TRACERS mission is the fact 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 reconnection process itself, including: Does reconnection turn off and on in time or does it happen in multiple places at the same time? 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. These missions entail placing instruments on rockets that fly on one trip into the cusp. TRICE-II, a sounding rocket mission, was in many ways the proof of concept for TRACERS. Two rockets were sent into the cusp at about the same separation that the two TRACERS satellites will follow (10-120 seconds), and they provided promising data. However, this was just one trip into the cusp after several years of work to build the rocket and instruments. The two TRACERS spacecraft will follow a relatively low orbit (~550km) that will take the two satellites through the cusp 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 at a time or from just one spacecraft in orbit, TRACERS will provide much more data under a range of geophysical conditions than has yet been possible.

Animation credit: Andy Kale

TRACERS partners