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2011-08-08 05:50:53
A thin band of antimatter particles called antiprotons enveloping the Earth has
been spotted for the first time.
The find, described in Astrophysical Journal Letters, confirms theoretical work
that predicted the Earth's magnetic field could trap antimatter.
The team says a small number of antiprotons lie between the Van Allen belts of
trapped "normal" matter.
The researchers say there may be enough to implement a scheme using antimatter
to fuel future spacecraft.
The antiprotons were spotted by the Pamela satellite (an acronym for Payload
for Antimatter Matter Exploration and Light-nuclei Astrophysics) - launched in
2006 to study the nature of high-energy particles from the Sun and from beyond
our Solar System - so-called cosmic rays.
These cosmic ray particles can slam into molecules that make up the Earth's
atmosphere, creating showers of particles.
Many of the cosmic ray particles or these "daughter" particles they create are
caught in the Van Allen belts, doughnut-shaped regions where the Earth's
magnetic field traps them.
Among Pamela's goals was to specifically look for small numbers of antimatter
particles among the far more abundant normal matter particles such as protons
and the nuclei of helium atoms.
'Abundant source'
The new analysis, described in an online preprint, shows that when Pamela
passes through a region called the South Atlantic Anomaly, it sees thousands of
times more antiprotons than are expected to come from normal particle decays,
or from elsewhere in the cosmos.
False colour bubble chamber image of antiproton/proton annihilation Antiprotons
"annihiliate" if they come into contact with normal protons
The team says that this is evidence that bands of antiprotons, analogous to the
Van Allen belts, hold the antiprotons in place - at least until they encounter
the normal matter of the atmosphere, when they "annihiliate" in a flash of
light.
The band is "the most abundant source of antiprotons near the Earth", said
Alessandro Bruno of the University of Bari, a co-author of the work.
"Trapped antiprotons can be lost in the interactions with atmospheric
constituents, especially at low altitudes where the annihilation becomes the
main loss mechanism," he told BBC News.
"Above altitudes of several hundred kilometres, the loss rate is significantly
lower, allowing a large supply of antiprotons to be produced."
Dr Bruno said that, aside from confirming theoretical work that had long
predicted the existence of these antimatter bands, the particles could also
prove to be a novel fuel source for future spacecraft - an idea explored in a
report for Nasa's Institute for Advanced Concepts.