An introduction to cosmic rays

It’s common knowledge that everyone on the planet is itching for the future of space exploration – which could very well include interplanetary travel, among other things. However, most experts agree that the idea of space travel isn’t going to be an easy task, especially since it puts us at the mercy of cosmic rays, which can spell bad news for those who are unprepared for it.

While the term itself looks like something out of a comic book, cosmic rays are actually atom fragments from outside the solar system that regularly strike the Earth. These rays, which travel at light-speed, are known to cause electronic problems, especially in satellites and other machinery.

For something that regularly rains down on the Earth, there’s a lot that we don’t know yet about cosmic rays. One thing that’s on everyone’s minds is where exactly they come from. Scientists, in general, believe that cosmic rays are related to supernovas; however, data from observatories around the world say otherwise, given that cosmic rays appear to be uniform in origin, something that supernovas aren’t.

That’s not to say that we’re completely stumped by cosmic rays. In a recent study published in Science, a team from Argentina’s Pierre Auger Observatory revealed that cosmic rays aren’t really that uniform. After measuring the arrival trajectories of over 30,000 cosmic particles, the researchers found that while their exact origins are still unclear, there is a difference in frequency of when the rays strike, based on its location. (Related: An introduction to the OMG particle: An ultrahigh-energy cosmic ray that is extremely fast.)

Practical applications of cosmic rays

Indeed, cosmic rays are nebulous at best, but that doesn’t mean that they can’t be used for real-world applications. As cosmic rays enter the earth’s atmosphere,they begin to interact with their surrounding atoms, creating a number of particles before finally reaching the ground. Among those that the interaction generates is a huge amount of particles called muons, which are able to get to the ground.

Muons, in particular, are able to deeply penetrate into matter, changing their absorption length to match the atomic number of the material. This behavior, which scientists refer to as muon tomography, can be used to detect the presence of heavy elements, radiation shielding, and fissile materials (or nuclear materials). This lends itself to industries like defense and national security, with some companies manufacturing cosmic ray detectors for this purpose.

However, the idea of using muon tomography for scanning objects isn’t a new or novel one. In 1965, physicist Luis Alvarez proffered the idea of muon tomography to look inside the Egyptian pyramids. By using cosmic rays and measuring their influx, Alvarez said that it could determine the presence of hidden chambers. While his experiment did not yield positive results, a recent survey on the Great Pyramid of Giza has found a “possible void” inside the structure using muon tomography.

Is it harmful?

While the jury is out on whether cosmic rays can cause damage for earth-dwellers (the World Health Organization says that our exposure isn’t high enough to have specific risks), scientists agree that it poses a real danger for those in outer space. Those on the Earth’s surface are protected from the full effects of cosmic rays and other forms of space radiation by its magnetic field; however, people outside of it are more likely to receive radiation equivalent to having a “whole-body CT scan every five or six days.”

In a study published in Scientific Reports, researchers from the University of Nevada, Las Vegas concluded that a person sent to a mission in Mars doubles his risk of developing cancer, following long-term missions outside the Earth’s magnetic field. According to study author and noted space physicist Francis Cucinotta, most long-term space missions and deep space missions expose a person to unavoidable levels of space radiation, including galactic cosmic rays.

“Current levels of radiation shielding would, at best, modestly decrease the exposure risks,” he added.

Learn more about cosmic rays and its other practical uses at

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