Nuts & Volts - September 2004

Near Space

even hundreds of thousands. Such events can last for only a few hours or several days. Solar cosmic rays represent a hazard for astronauts traveling outside of the Earth’s protective magnetosphere. Fortunately, our Apollo astronauts made their lunar expeditions during a time of solar quiet.

Anomalous Cosmic Rays

These are the nuclei of difficult to ionize atoms. They originate as neutral atoms drifting into the solar system from interstellar space. When exposed to solar ultraviolet radiation, these atoms become ionized. Once ionized, the solar wind can capture them and carry them away from the solar system. When traveling with the solar wind, these ions are called “pickup ions.”

Pickup ions are carried to a point where the solar wind is forced to slow down from supersonic to subsonic speeds by the resistance of the local interstellar medium. This region — where solar wind flow goes from supersonic to subsonic — is called the terminal shock. Smaller versions of terminal shocks are seen within the solar system when the solar wind plows into the magnetosphere of planets.

The passage through a terminal shock can accelerate pickup ions and change their direction of travel.

After multiple passes through the terminal shock, these cosmic rays can break free and travel back into the solar system, where they can be detected. The remaining, anomalous cosmic rays escape the solar system and travel between the stars.

Anomalous cosmic rays have intermediate energy levels and are representative of the atoms found in nearby interstellar space. They are influenced by the 11 year solar cycle, which changes the location of the Sun’s terminal shock.

Galactic Cosmic Rays

These cosmic rays are the highest energy cosmic rays we find. They are fully stripped of their electrons. Galactic cosmic rays probably originate in supernova remnants, which are the expanding clouds of gas and dust that were once the outer layer of a massive star. The explosion itself didn’t create the cosmic rays. Instead, the powerful and expanding magnetic fields and shock waves associated with supernova remnants accelerate ionized atoms.

After the ions pick up enough energy, they can escape from the supernova remnant as galactic cosmic rays and travel interstellar space. We know supernova remnants can accelerate charged subatomic particles because the

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NUTS & VOLTS E v e r y t h i n g

In an effort to share current information with this column’s readers, I have created an Email distribution list under Yahoo! Groups. My Email list is not designed to replace the many lists for amateur near space groups that already exist. I plan to make announcements, update column information, and answer reader questions in this list. I will also keep subscribers up-to-date on the status of my book on amateur near space exploration.

To join the Near Space Email group, go to

http://groups.yahoo.com/

Sign in if you’re already a member of Yahoo!

— if not, click under New Users, then Click Here To Register.

Under the Join a Group field, type NearSpace and then press Enter.

Under the list of groups displayed, click NearSpace (it will be the only group listed).

In the upper right of the screen, click to join the group.

I hope you find the Email list useful in your efforts to begin your own program of amateur near space exploration.

radio signals the remnants emit indicate the presence of powerful magnetic fields that are accelerating electrons.

When the charged electron accelerates, it emits a radio wave called synchrotron radiation. The study of the isotopes found in galactic cosmic rays and their half lives indicates that these cosmic rays can travel for several million years before being detected on Earth.

Most galactic cosmic rays have low enough energies that the Milky Way’s magnetic field bends their paths around a radius smaller than the galaxy. This effectively traps these lower energy galactic cosmic rays within the Milky Way galaxy. However, a small percentage of the galactic cosmic rays contain more energy than is available in supernova remnants.

Their energies are too great for them to be held within the galaxy’s magnetic field. So, these ultra-high energy cosmic rays must originate outside the galaxy. However, these high speed cosmic rays cannot travel for long through intergalactic space before their collisions with photons left over from the Big Bang (the cosmic microwave background) significantly lower their energies.

It’s believed these ultra-high energy cosmic rays originate in nearby, active nuclei galaxies, which appear to be powered by massive black holes. Perhaps, instead, these cosmic rays are trying to tell us about exotic physics occurring deep within intergalactic space.

One of the benefits of galactic cosmic rays is that their collisions with atoms in interstellar gas create some of the rare elements needed for life, but that are not synthesized by the fusion reactions within the stars.