The antiprotons lie
sandwiched between the inner and outer Van Allen belts
(in red) around the Earth
A thin band of antimatter particles
called antiprotons enveloping the Earth has been spotted for
the first time.
described in Astrophysical Journal
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
The researchers say there may be
enough to implement a scheme using antimatter to fuel future
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
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.
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.
Antiprotons "annihilate" 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
"annihilate" in a flash of light.
Although normal matter particles
outweigh the antiprotons by thousands to one, 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