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The Plan to Make the Moon an Enormous Detector of Cosmic Rays

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About once a century on any given square kilometer of Earth, a cosmic ray hits with mind-boggling intensity. The teeny tiny subatomic particle from space comes careening in with more than 10 million times the energy of particles shot out by the LHC. Where do these ultrahigh energy cosmic rays come from? Astronomers have a plan to find out, using the moon and a massive new radio telescope array.

The array, which is in development now, is so massive that doesn't fit on one continent. Spread out over thousands of miles across Australia and South Africa will be thousands of radio telescopes that, together, add up to the Square Kilometer Array. The total collecting area of the array is one million square meters, or one square kilometer, hence its name. When it's completed in 2024, it will be the world's biggest and most sensitive radio telescope.


Artist impression of the Square Kilometer Array. Credit: SKA

But what about the moon? Here's where things get interesting. In a paper recently posted to ArXiv, a group of astronomers detail how the entire moon can be turned into an instrument for studying the mysterious cosmic rays. That's because upon impact, cosmic rays generate a cascade of secondary particles, which can be seen as nanosecond burst of radio waves. By analyzing these radio waves, we might figure out where the rays are coming from.


There is a catch, of course, which explains why the moon isn't already a cosmic ray detector. The Physics ArXiv blog explains:

This effect is complicated by the fact that radio pulses are projected forward in a cone and cannot travel far through the lunar surface before being absorbed. That means that astronomers will only be able to see the radio pulses from ultrahigh energy cosmic rays that graze the edge of the Moon coming our way. So the gear they need to detect the signal is a highly sensitive radio telescope on Earth.

That is where the Square Kilometer Array comes in. If all goes according to plan in the next decade, we could see these small perturbations on the moon—and begin to solve some of the mysteries of space. [The Physics ArXiv Blog, ArXiv]

Top image: Peter Freiman/Creative Commons