Antimatter galaxies and dark matter have long haunted
physicists' theories, but no instrument in orbit has had the power to confirm
or deny their existence. Now a $1.5 billion cosmic ray detector scheduled for
launch in 2010 could usher in a new era for discovering all that's weird and
wonderful about the universe.
Cosmic rays consist of high-energy particles that emerge
from catastrophic events such as
supernovas, and may also hold the clues to whether antimatter galaxies and dark
matter truly exist. Detecting cosmic rays firsthand from the ground has
proved difficult, because they collide with atoms in Earth's atmosphere and
break up into a shower of secondary particles.
"Earth's atmosphere absorbs everything, so you cannot
study primary cosmic rays until you go to space," said Samuel Ting, an MIT
physicist who first proposed a large cosmic ray detector back in 1994.
Now just months from completion, the Alpha Magnetic
Spectrometer (AMS) represents years of work by NASA and the Department of
Energy to overcome the challenges of putting a superconducting magnet into
space. It also holds the hopes of an international physics community that wants
to finally tackle some of the longest-standing questions behind the universe.
The mission to launch the spectrometer was initially canceled by NASA in the wake of the 2003 Columbia tragedy. But NASA reinstated it after Congress approved funding for an extra shuttle flight to the International Space Station. That flight is slated to launch in either July or September 2010.
Bend it like a magnet
A large superconducting magnet allows AMS to analyze the
charged particles of cosmic rays, given that the particle paths curve in the
presence of magnetic fields. The charged particles then pass through a number
of detectors that allow scientists to figure out whether the particles are
protons or electrons, or even anti-electrons known as positrons that might
signal the existence of dark matter.
Crunching the data from the sensors requires an onboard
supercomputer that combines 650 computer units and uses 2.5 kilowatts of power
— far more power than a satellite's solar panels can normally provide. That
means AMS must find a home on the International Space Station, where the Canadian
robot arm will help install the instrument on an outside truss.
But putting a magnet in space has long frustrated scientists
because of the magnetic compass effect, Ting told SPACE.com. Just as the
magnet in a compass rotates to point north due to Earth's magnetic field, the
large AMS magnet would want to rotate along with the entire space station.
"The task of building a space-qualified superconducting
magnet is a very, very hard one," said Ben Monreal, a physicist at the University
of California in Santa Barbara. He worked on one of the AMS sensors as a grad
student at MIT, but also observed how engineers at NASA and Space
Cryomagnetics, Ltd. worked around the magnet problem.
Engineers ultimately used a set of racetrack coils that canceled
out the dipole magnetic field outside AMS, and will prevent the instrument from
giving space station residents a case of the dizzies.
Catching bigger fish than CERN
An Italian satellite called
PAMELA launched in 2006 with the capability of detecting some antimatter
particles such as positrons. But AMS has about 250 times the sensitivity of
such existing instruments for detecting high-energy particles.
The AMS magnetic setup also resembles that of the Large
Hadron Collider, or the most powerful particle accelerator in the world located
at CERN in Switzerland. The underground particle accelerator sends protons
zooming around a 17-mile-long circular track and smashes them together to
create combined energies of 7 tera-electronvolts (TeV).
Still, that fades in comparison to cosmic ray particles that
may have energies of 100 million TeV or more.
"The space station [AMS device] can detect particles of
practically unlimited energy," Ting noted. Those include positrons that may
suggest collisions between particles of dark matter thought to make up 90
percent of the universe.
Finding evidence of anti-helium or heavier antimatter
elements could also provide strong proof of antimatter galaxies, given that the
heavier elements would only emerge from stars in an antimatter galaxy. AMS
would cover any possible antimatter galaxies out to about 1,000 megaparsecs, or
about the edge of the observable universe.
Bumpy space odyssey
The 15,000 pound cosmic ray detector remains just months
away from delivery to NASA's Kennedy Space Center in Florida, where it can prep
for a 2010 launch to the space station aboard one of the last space shuttle
flights. But physicists can still recall the long battle to move AMS forward to
this point.
One of the bleaker moments came after NASA lost the space
shuttle Columbia in a 2003 tragedy. The space agency told physicists that
no room existed for AMS aboard remaining shuttle flights, at least until more
recent schedule reshufflings that added shuttle flights.
"It's been up and down," Monreal recalled. "I
can think of three or four cycles where it looked [like] it was completely
dead, and then things looked up."
Ting and other physicists have already begun working around
the clock to ensure that everything checks out with the cosmic ray detector.
They also plan to monitor AMS 24 hours a day, seven days a week after launch using a control room and working in shifts. The plan, they hope, will help to hit scientific pay dirt when the instrument begins analyzing the
heavens.
"Certainly for me, it's the most difficult experiment
I've ever done," Ting said. "That's why we want to take the time to
get it right."
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