Cosmic rays from space hit Earth's atmosphere all the time. When a high-energy cosmic ray enters the atmosphere, it can cause an "air shower". The cosmic ray hits a molecule in the atmosphere and "breaks up", producing lots more sub-atomic particles. A real air shower can make millions of particles. This picture shows a simple version of an air shower. The cosmic ray (in red, at the top) makes lots of other particles, many with odd names. The sub-atomic particles shown here include protons (green), neutrons (orange), pions (yellow), muons (purple), photons (blue), and electrons & positrons (pink).  Windows to the Universe original artwork by Randy Russell using a photo courtesy UCAR (Nicole Gordon).  This image and text is from Windows to the Universe®( http://windows2univers.org ) © 2010 National Earth Science Teachers Association.   This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.  [5]

Cosmic rays from space hit Earth's atmosphere all the time. When a high-energy cosmic ray enters the atmosphere, it can cause an "air shower". The cosmic ray hits a molecule in the atmosphere and "breaks up", producing lots more sub-atomic particles. A real air shower can make millions of particles. This picture shows a simple version of an air shower. The cosmic ray (in red, at the top) makes lots of other particles, many with odd names. The sub-atomic particles shown here include protons (green), neutrons (orange), pions (yellow), muons (purple), photons (blue), and electrons & positrons (pink).

Windows to the Universe original artwork by Randy Russell using a photo courtesy UCAR (Nicole Gordon).

This image and text is from Windows to the Universe®(http://windows2univers.org) © 2010 National Earth Science Teachers Association.   This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.  [5]

The Science Behind the Cosmic-Connection

The core of our sculpture is a spark chamber which produces electric arcs along the path that cosmic rays take through the sculpture.   Spark chambers were the primary means that physicists used in the 1970s to visualize particle paths before modern electronics were developed.  The cosmic rays ionize the helium gas in the chamber and the voltage between the plates causes current to flow.   All this happens very rapidly; the particle passes though in a billionth of a second and the 10,000 volts must be applied within ½ of a millionth of a second or the electrons recombine with their helium atoms, no arc will occur, and you can’t see anything. 

But what are these cosmic rays which we are observing?

Cosmic Rays are high energy particles originating in space coming down into the atmosphere.   They were discovered in 1912 when Victor Hess measured radiation from a balloon launch and determined that the radiation increased with altitude [1,2].   Low energy cosmic rays are produced by our sun and are almost entirely blocked by our atmosphere.  These particles can pose a hazard to astronauts, though, and are a significant issue to deal with on a flight to Mars.   The higher energy cosmic rays are born in our galaxy and beyond.  Some come down with energies significantly higher than that produced by the largest particle accelerators on Earth.  They come in from all directions of space.   Most of the particles are hydrogen and helium nuclei but some are heavier elements such as iron.  The composition and energy of these particles can teach us many things.

For example we know that they are mostly normal matter; not antimatter.   This shows us that our galaxy is made of normal and not antimatter (matter with the opposite electric charge).  One of the mysteries of the origin of our universe is why it is primarily made of normal matter and not half of each.   Another thing we can determine from the radioactive decay of the iron nuclei cosmic rays is that they come from places like the Crab Nebula which is filled with hot young stars [3].   We determine this by knowing how much of the iron has decayed and how fast it is travelling.  We then know how long ago it was created and how far it has traveled.   Some other very high energy cosmic rays are thought to originate in explosions of stars (supernovae) or black holes [4].

When the particles strike the atmosphere they can set off a cascade shower of various particles which come down to the ground (see the illustration).  Many of the particles which reach the ground are muons, a charged particle which weighs about 400 times what an electron does.  These cascade particles still have high energy and one goes through your body about every second.    You’d need to be shielded by more than 6 feet of concrete to get rid of most of them.   Even then some of the highest energy particles would get through.   This radiation represents about 1/3 of the natural radiation exposure your body receives.  Airplane pilots get about three times as much because they are flying above much of the shielding effect of the atmosphere.   You get a bit more in Black Rock City than in San Francisco (but less than in Denver!).

You’ve probably heard of carbon dating of artifacts.  This radioactive carbon (carbon-14) is produced in the atmosphere when a cosmic ray strikes a nitrogen nucleus.  The constant production rate and known radioactive decay rate allow us to estimate how old things are by seeing how much of the carbon -14 remains after the organism grew and incorporated the carbon.

Though they were discovered over 100 years ago the study of cosmic rays continues to teach about the universe, astro-, and nuclear physics.  See the references below for more information.

References

 [1] https://en.wikipedia.org/wiki/Cosmic_ray

[2] https://home.cern/about/physics/cosmic-rays-particles-outer-space

[3] https://www.nasa.gov/press-release/goddard/2016/ace-cosmic-ray

[4] Ackermann, M., et al. "Detection of the Characteristic Pion-Decay Signature in Supernova Remnants". Science. American Association for the Advancement of Science. 339 (6424): 807–811 (2013).

[5] http://www.windows2universe.org/physical_science/physics/atom_particle/cosmic_rays.html&nl=2