EMBARGOED FOR 2 p When Marco Casolino flies on commercial airliners, he always hopes he'll see things, just like the astronauts do. So far he's had no luck. But a new study he led helps explain what it is he's looking for.
Since the Apollo 11 mission, and perhaps before, astronauts have been seeing things in space: colorful dots, streaks and flashes spotted when their eyes were closed or when the inside of the spacecraft was dark. During one trip to the Moon, astronauts observed a flurry of activity, in green, which they described as being like a St. Patrick's Day display.
Some scientists scoffed at the ghostly observations and at the prediction from the pre-Apollo era that such a phenomenon could occur.
Nobody is scoffing now. New results from Casolino, of the National Institute of Nuclear Physics at the University of Rome, Tor Vergata, move scientists closer to understanding how cosmic rays apparently generate these mysterious light flashes, as they are called.
Cosmic rays are highly energetic, charged particles -- mostly protons -- that originate throughout the galaxy when stars explode, scientists believe. They constantly bombard astronauts. They can penetrate a spacecraft and the human body. Earth's atmosphere and magnetic field, however, mostly protect the planet from this perpetual onslaught.
Before anyone ever went to space, Cornelius Tobias, a Lawrence Berkeley National Laboratory expert on the biological effects of radiation, suggested in 1952 that cosmic rays might interact in some way with the human visual system, which is designed to perceive photons, not protons. He later tested the idea -- on himself and colleagues -- using a particle accelerator, but the tests were discontinued because of health concerns.
"You see visual flashes," Tobias later said, prior to his death in 2000. "It is an exhilarating sensation. It is as though you are looking into the universe itself."
The eye turns out to be a more amazing detector than anyone but Tobias imagined.
"To our knowledge, light flashes are the only way that a human can 'see' elementary particles directly, without the use of instruments," Casolino told SPACE.com in an e-mail interview describing his new research.
Close your eyes and watch
To learn more about the strange phenomenon, Casolino and his collaborators outfitted cosmonauts aboard the Mir Space Station (before it was
de-orbited in 2001) with special helmets that contained built-in particle detectors. The cosmonauts measured particle rates while recording the number of flashes they saw. The work builds on similar but inconclusive experiments conducted aboard Apollo missions.The frequency of flashes aboard Mir did not correspond to the numbers of protons, suggesting another process was also at work, Casolino and his colleagues will report in tomorrow's issue of the journal Nature. The researchers conclude that rarer cosmic ray particles -- the nuclei of helium, carbon, nitrogen and oxygen -- are also involved.
The flashes can originate through direct interactions with the retina or the optic nerve, Casolino said, or nuclear interactions in the eye that in turn affect the retina, where normal images are received after light passes through the eye's lens.
There are no known health dangers associated with light flashes. But cosmic radiation in general is hazardous. Reactions can destroy cell nuclei and put astronauts at increased risk for cancer and make them more susceptible to other diseases, researchers believe.
Present knowledge of light flashes, Casolino said, suggests that merely monitoring radiation might not give a complete picture of the effects of cosmic rays, and a detailed understanding of the flashes could improve efforts to safeguard future space travelers.
Casolino's team is now analyzing data from a more sophisticated test conducted last year on the International Space Station. In addition to monitoring incoming particles, the study used an electroencephalograph to monitor brain activity during light flashes.
Do you see what I see?
For anyone on the ground who sees things and has been wondering if cosmic rays might be to blame, Casolino can't be sure, but he has doubts.
The observations of flashes are extremely subjective and vary from one person to another, he notes. But few cosmic rays survive the trip through Earth's atmosphere. Most decay into other particles, such as muons, which provide little or no opportunity for generating flashes.
Further, Casolino said, the brain may well dismiss flashes as unimportant, not even allowing us to notice them. Other physiological conditions, such as differing blood pressure, might cause similar apparent perceptions.
Jet passengers above much of the atmosphere ought to have a better opportunity, however, to get a taste of the odd visual experience astronauts describe.
"I try to look for light flashes when I'm on a plane, but up to now I have seen nothing," Casolino said. "The problem is that it is difficult to know what you are looking for."
Airline Pilots Report a Different Sort of Flash
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