On January 4, 201
CAPER-2, short for Cusp Alfvén and Plasma Electrodynamics Rocket-2, is a rocket mission – a kind of spaceship that carries scientific instruments on short, targeted voyages into space before it falls back to Earth. In addition to their relatively low price and fast development time, rockets are ideal for entry into temporary events – such as the sudden emergence of the Aurora Borealis or Northern Lights.
For CAPER-2 scientists flying through an aurora provides insight into a process as fundamental as it is complex: how are particles in space accelerated? NASA is investigating this phenomenon not only to better understand the Earth's space environment but also to protect our technology in space from radiation, but also to understand the nature of stars and atmospheres in the Solar System and beyond.
"Throughout the Universe you have charged particles that are accelerated – in the solar atmosphere, in the solar wind, in the atmospheres of other planets and in astrophysical objects," said Jim LaBelle, space physicist at Dartmouth College, Hanover, New Hampshire and principal investigator for the CAPER 2 mission. "An Aurora provides us with a local laboratory where we can observe these acceleration processes nearby."
Technically, the CAPER 2 team is interested in what happens just before an aurora starts to glow. Electrons that flow from space into our atmosphere collide with atmospheric gases and trigger the glow of the aurora. Somehow they are on the way to speed.
"As they fall into our atmosphere, these electrons move ten times faster than before," said Doug Rowland, a space physicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who also studies particle acceleration. "We still do not understand the fundamental physics of how that happens."
The CAPER 2 team focused on a special kind of aurora that forms during the day. Unlike the nocturnal aurora, the aurora is triggered by electrons that flow in directly from the sun during the day – and we know much less about it.
"There was a great deal of research into the regular Aurora during the night, but the Aurora day is much less explored," said Craig Kletzing, space physicist at the university from Iowa in Iowa City and co-investigator of the mission. "There are good signs that there are some similarities, and there are also differences."
The team focuses on how the electrons that generate Aurora during the day are shuffled by waves. Two types of waves are of particular interest and have opposite effects. Alfvén waves, named after the Swedish Nobel laureate Hannes Alfvén, who for the first time predicted their existence in 1942, are said to accelerate the electrons. These giant waves, measuring tens to hundreds of miles from tip to tip, propagate along the Earth's magnetic field lines, driving electrons back and forth.
On the other side are Langmuir waves, which are generated by the electrons themselves – a process that steals some of the energy of the electrons and slows them down. CAPER-2 will carry a high-resolution wave-particle correlator to measure, the first missile mission to do so for the daylight aurora.
"This is very data intensive," said LaBelle. "It is unique to sounding rockets to be able to view this mechanism in this level of detail."
At the start, the CAPER 2 team traveled to Northern Norway, one of the few places where rockets are in range of the day Aurora. Northern Norway turns every day under an opening in the Earth's magnetic field, known as the North Pole Peak, where particles from the Sun can reach our upper atmosphere. This is far too large to replicate in a laboratory.
"It's a kind of natural laboratory," LaBelle added. "We conduct our experiment in two different environments where the variables are different and test the theory and answer the questions."
NASA is planning a twin-rocket launch over Norway this winter