Radar astronomy is a crucial tool in measuring the trajectories of Earth-crossing asteroids. If we’re going to be hit, radar is how we’ll work out when. The technique has also been used to image various bodies such as the asteroid 216 Kleopatra, to measure distances with extreme accuracy and to test relativity by monitoring the orbit of Mercury.
The technique was first used in the 1960s and since then astronomers have broadcast some 1400 radar transmissions towards the heavens, says Alexander Zaitsev at the Institute of Radioengineering and Electronics, Russian Academy of Sciences, in Fryazino near Moscow. These transmissions have lit up about 2×10^-3 part of the sky.
By contrast, humanity has broadcast only 16 messages intended for extraterretrial consumption. And these have illuminated an area of sky some 2000 times less than the radar astronomy signals.
Since the radar signals were 500 times longer than the ET messages, Zaitsev says that ET is about 1 million times more likely to pick these up first. So first contact is likely to be a little more prosaic than most of us had anticipated.
The purpose of Zaitsev’s calculation is to take on the chicken little’s who say that we should keep our interstellar gobs shut lest some hostile super-civilisation decide to turn us all to astroslavery. He says these people should be more worried about radio astronomy than ET messages and since we can’t stop monitoring Earth-crossing asteroids, the party poopers might as well give up and go home.
It’s all irrelevant anyway. If ET was going to make herself known, she’d have done it by now.
Ref: arxiv.org/abs/0804.2754: Detection Probability of Terrestrial Radio Signals by a Hostile Super-civilization