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Ask Dr. SETI ®

Chapter 1: Astrophysics

Can SETI Detect Asteroids?

Dear Dr. SETI:
Could SETI data be used to detect near Earth asteroids? With so much interest in asteroids being generated by the news media, it would be interesting to see if SETI data could be used to find these objects. Would a large asteroid be able to block enough of the microwave background noise to show up as a hole in the data?

Terry (via the Internet)

The Doctor Responds:
Great question, Terry. The short answer is, probably not. Although the universal microwave background radiation is about 3 Kelvin, most celestial objects (including asteroids) are much warmer, and give off thermal radiation of their own. Thus they do not decrease, but rather increase received signal levels. Unfortunately, the angle subtended by asteroids as viewed from Earth is many orders of magnitude less than the beamwidth of even our largest radio telescopes. Thus, it is unlikely we will resolve them at microwave frequencies. But wait, there's more.

Near Earth asteroids bode well for SETI for a completely different reason. If other civiliations, perhaps just a little more advanced than ours, are concerned about their planets being smacked flat by a falling mountain, then they probably have asteroid alert search radars. We know what the general characteristics of such radars would need to be to fulfill their mission. And such radar signals, if they happen to glance in our general direction, can be easily detected on Earth, from hundreds of light years away. So SETI has yet another class of artificial emissions to search for in our quest for our cosmic companions.

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