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Out Of The Noise
"One person's noise is another's signal"
A Cosmic Effect - Good & Bad, But Not Indifferent!

by WKT
February 15, 2002 ::
HDFN
Hubble Deep Field - North
(Credit: NASA/Penn State)
"Why should we care what happens in our galaxy and beyond? Sure it's nice to know something about galaxies, black holes, supernovas, etc.,... but it's all so far away and there are so many pressing problems on Earth that need our attention!"

Granted, there are lots of problems here on Earth that are deserving of attention, but that's not the point. We are in fact very much affected by the cosmic environment that we inhabit. Maybe not in the way the daily astrology columns portend, but in real, practical ways. Some of these effects may be the source of "Earthly" problems, and some of them can be used in the search for solutions to problems. Take for example, cosmic rays.

X-ray image of our Sun
X-ray image of our Sun, courtesy of The Soft X-ray Telescope on board the Yohkoh satellite
Spaceship Earth makes a 500-million mile journey around the sun each year. Throughout this journey a thin rain of cosmic rays - high-energy particles - produce a background of ionizing radiation on Earth. Some of these cosmic rays are produced by flares on the sun. Others come from explosive events in our galaxy, and still others, with very high-energies, may come from other galaxies.

The bad news is that our bodies are continually bombarded by cosmic rays which damage or disrupt our molecules, and are thereby potentially harmful to our health. The radiation doses increase at higher altitudes and can become especially dangerous to astronauts, and passengers and crew on high-altitude airplanes during a solar flare. Another bit of bad news is that cosmic rays can and do cause glitches in the operation of our computers.

The good news is that all this cosmic disruption of atomic and subatomic particles can be put to use to help answer questions and solve problems. As cosmic rays, which are mostly high-energy protons, tear through Earth's upper atmosphere, they initiate nuclear reactions that change the nuclei of certain atoms. Some of these mutated nuclei, in the form of carbon-14 nuclei, can be identified and used as clocks to date the charred embers of ancient campfires as well as bones and cloth.

Recently, with the development of powerful new mass spectrometers - particle accelerators that whirl nuclei around at dizzying speeds and use their orbits to determine their masses - scientists are using cosmic ray produced nuclei - called cosmogenic nuclides- to study the history of the Earth itself.

The principle is the similar to that for carbon-14. Cosmic rays produce cosmogenic nuclides of beryllium-10 and aluminum-26 in quartz crystals of rock and sand while they are exposed to the cosmic weather. The longer a quartz crystal is exposed, the more nuclides it accumulates. Erosion then dumps the quartz crystals into lakes and rivers where geologists can scoop them up and determine how long the crystals were exposed.

Cosmic Ray Schematic Stream
Isotopes formed by collisions with cosmic rays (wavy blue lines) in exposed rock and sand crystals (left) are washed down into streams where the sediment can be collected by geologists. (Credits: Cosmic Ray Schematic: C. Slayden; Photograph: Jim Kirchner)
This new technique has been used by Darryl Granger of Purdue University to show that the ice sheet that formed Mammoth Cave in Kentucky arrived about 1.5 million years ago, about 700,000 years earlier than previously thought. At the other end of the scale, a group led by Friedhlem von Blanckenburg in Switzerland found that the onset of cultivation in the rain forest of Sri Lanka increased erosion as much as 100-fold. Cosmic rays help us to understand the importance of sustainable agricultural practices.

Over the long haul, one might think that mountains wear down at a fairly steady rate. Not so, discovered Jim Kirchner of the University of California, Berkeley. His study of Idaho's mountains revealed that erosion rates over the past 5,000 to 27,000 years were 17 times higher than modern-day rates. Kirchner concluded that rare catastrophic events, such as wildfires followed by floods were responsible for most of the erosion. This information is useful for engineers in estimating the time it will take reservoirs to fill with debris.

That cosmic-ray dating techniques should demonstrate the importance of catastrophes in shaping the Earth is fitting in a way, because most of the cosmic rays that rain down on Earth are probably due to cosmic catastrophes known as supernovas.

E0102
X-ray/Optical/Radio Overlay of E0102-72.3
(Credit: X-ray: NASA/CXC/SAO, Optical: NASA/HST, Radio: CSIRO/ATNF/ATCA)
Supernovas, which signal the end of the life of a massive star, produce brilliant flashes of light and awesome shock waves that rip through interstellar space at speeds of millions of miles per hour. Part of the energy of a supernova shock wave goes into the production of hot gas that can be observed with an X-ray telescope. Another portion goes into the acceleration of electrons, protons and heavier nuclei to speeds approaching the speed of light. These particles eventually escape into the Galaxy and become part of the cosmic ray flux through which the Earth moves.

John P. Hughes of Rutgers University and his colleagues used the high spatial resolution of the Chandra X-ray Observatory to make a detailed study of amounts of energy in hot gas and cosmic rays produced by a supernova shock wave. They found that as much as 25 percent of the energy could go into cosmic rays. This is strong evidence in support of the idea that supernovas in our galaxy produce many of the cosmic rays that affect our lives and inform us about life on Earth.

References: J.P. Hughes et al. 2000 Astrophys. J., 543, 61 L. Greensfelder, Science, 295, 256 (11 Jan 2002) M. Friedlander, Cosmic Rays, (1989, Harvard U. Press)

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