High above the ice in Antarctica, a group of enormous balloons was quietly tracking a phenomenon that could not be seen from the ground.
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that → track → ground
In January 2013, Nasa's BARREL mission sent 20 balloons drifting through the polar winds, carrying instruments designed to detect faint X-rays produced when energetic particles entered Earth's upper atmosphere.
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particles → send → atmosphere
The experiment was part of a much larger effort to understand what happens inside the Van Allen radiation belts, where charged particles can become trapped by Earth's magnetic field and later escape towards the poles.
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particles → understand → poles
As the balloons moved with the winds, their measurements were matched with observations from Nasa's Van Allen Probes, which were travelling through the radiation belts themselves.
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which → move → belts
The unusual pairing gave scientists a chance to examine both ends of the same process: particles moving through near-Earth space and the traces they left behind when they reached the atmosphere.
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they → give → atmosphere
Nasa’s BARREL mission: How 20 giant balloons were used in 2013 to track X-rays over Antarctica
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balloons → use → Antarctica
The first Antarctic BARREL campaign involved 20 balloons.
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campaign → involve → balloons
They were released at intervals of roughly a day or two, allowing the team to build up a spread of measurements as the balloons moved with the circumpolar winds.
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balloons → release → winds
According to Nasa, when fully inflated, a BARREL balloon was about 90 feet (27 metres) across, while the scientific payload underneath was relatively small.
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payload → accord → Nasa
Each flight carried instruments capable of detecting X-rays generated high in the atmosphere.
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flight → carry → atmosphere
The balloons could remain airborne for several days, and some stayed aloft for as long as 40 days.
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some → remain → days
The launch sites included the South African National Antarctic Expedition base at SANAE IV and Halley Research Station.
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sites → include → IV
Antarctica offered a useful vantage point because Earth's magnetic field guides charged particles towards the polar regions.
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field → offer → regions
That made the continent a practical place to watch radiation belt particles arriving in the atmosphere.
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continent → make → atmosphere
PC: Nasa
How scientists tracked particles escaping Earth’s radiation belts
The balloons were not primarily studying Antarctica or its atmosphere.
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balloons → track → Antarctica
Earth is surrounded by the Van Allen radiation belts, regions containing energetic charged particles held in place by the planet's magnetic field.
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Earth → surround → field
The population of these particles changes as conditions in near-Earth space respond to activity from the Sun.
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conditions → change → Sun
During periods of disturbance, the radiation environment around Earth can become more hazardous for spacecraft.
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environment → become → spacecraft
Particles do not simply remain trapped in the belts.
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Particles → remain → belts
Some are scattered out and travel along Earth's magnetic field lines towards the atmosphere.
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Some → scatter → atmosphere
Understanding how quickly this happens, and under what conditions, helps scientists build a clearer picture of how the belts gain and lose energetic particles.
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belts → understand → particles
Why scientists looked for X-rays in the atmosphere
An energetic electron falling into the atmosphere does not arrive unnoticed.
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electron → look → atmosphere
When these particles collide with atoms and molecules, they can produce X-rays.
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they → collide → rays
BARREL's instruments were built to detect that radiation.
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instruments → build → radiation
This gave scientists an indirect way of counting and studying particles that had escaped the radiation belts.
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that → give → belts
Instead of trying to follow every electron individually, the balloons measured the X-ray signature produced when populations of energetic electrons reached the atmosphere.
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populations → try → atmosphere
The balloons were effectively watching the consequences of particle loss while another spacecraft was measuring conditions inside the radiation belts themselves.
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spacecraft → watch → belts
How scientists tracked particles from space to the atmosphere
Reportedly, BARREL was designed to work with Nasa's Van Allen Probes, two spacecraft launched in 2012 to travel through the radiation belts.
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BARREL → track → belts
The satellites could measure the particles, fields and waves present in the belts, while the balloons observed the particles that had already begun making their way into the atmosphere.
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that → measure → atmosphere
When observations from the two missions overlapped, scientists could compare the conditions in space with the resulting precipitation into the atmosphere.
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scientists → overlap → atmosphere
This was particularly useful during periods of geomagnetic activity, when the behaviour of the radiation belts could change.
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behaviour → change → belts
The aim was not simply to collect two separate sets of measurements.
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aim → collect → measurements
By putting the observations together, the researchers could investigate whether changes seen inside the belts matched increases or decreases in the particles reaching the atmosphere.
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changes → put → atmosphere
The magnetic pathways that made the poles important
The choice of polar regions was tied to Earth's magnetic field.
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choice → make → field
Its field lines extend towards the northern and southern magnetic regions, providing pathways along which charged particles can move into the upper atmosphere.
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particles → extend → atmosphere
That is why the broader BARREL mission eventually operated in both hemispheres.
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mission → operate → hemispheres
The first campaigns, however, were conducted in Antarctica in 2013 and 2014.
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campaigns → conduct → 2013
Later campaigns included balloon flights from Sweden, above the Arctic Circle.
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campaigns → include → Circle
Nasa describes the mission as studying X-rays in Earth's atmosphere near both the North and South Poles.
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Nasa → describe → Poles
So the description of BARREL as a polar balloon experiment covers the mission as a whole, rather than meaning that the original January 2013 flights took place at both poles.
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flights → cover → poles
…and 12 more, not listed.
The Aporia
