THE most sensitive detector ever built to study cosmic rays from both normal and exotic sources was sent into orbit last week. The instrument will also look for hints of antimatter.
The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (Pamela) was launched from Kazakhstan on 15 June. The 470-kilogram experiment, a collaboration of German, Russian, Italian and Swedish scientists, will study all kinds of cosmic rays for three years, far longer than the few days provided by earlier space-based detectors, flown either on balloons or on the space shuttle.
Key to Pamela鈥檚 success will be its ability to study the properties of individual cosmic ray particles. 鈥淲e can recognise the particles鈥� charge, momentum, energy, everything,鈥� says team member Piergiorgio Picozza of the University of Rome Tor Vergata in Italy.
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Pamela will be able to detect cosmic rays from known sources such as supernovae, and possibly from other sources such as stars made of antimatter. Matter and antimatter have the same mass, but the opposite charge. The universe is thought to have contained equal amounts of the two immediately after the big bang, although we can only detect matter today. Some theorists think that while matter and antimatter annihilated each other, a slight excess of matter was created in the big bang, giving us the universe of today. Others believe that the primordial antimatter was not destroyed but simply ended up in a region of the universe that does not come into contact with normal matter.
If so, some charged antiparticles from those regions could make their way into our cosmic neighbourhood. Pamela will look for heavier antimatter particles that would have been forged in the early universe or in antimatter stars. This may help determine whether any antimatter regions exist in the universe.
鈥淢ost people would agree it is a long shot,鈥� says Richard Mewaldt of the California Institute of Technology in Pasadena, who is not part of the team. Nevertheless he says the mission will provide a valuable insight into antimatter. 鈥淭his has long been a search that people have wanted to conduct.鈥�
