The next time your car radar detector goes off it may not be due to the state police, but instead a snoopy beam from a nearby extraterrestrial civilization. The aliens wouldn't care less if you were breaking the speed limit, but they would use radar to study Earth's rotation, surface topography, and even the footprint of major cities. (Hopefully not for targeting weapons of mass destruction!)
Though it's improbable that alien radar would pack so much energy to trigger a dashboard radar detector, the idea of aliens probing us with radar isn't as outlandish as it sounds.
PHOTOS: 13 Ways to Hunt Intelligent Aliens
Interstellar beams powerful enough to bounce off extrasolar planets are well within the laws of physics and achievable technology - unlike the warp drive. The only showstopper is the price tag, it would be sky high.
Nevertheless, "radar probing" of nearby exoplanets offers a lot more potential information than teasing out a planet's chemical composition via a huge space telescope. Radar observations could tell us about the planet's rotation rate, axial tilt, surface roughness, penetrate cloud cover to map ocean shorelines, detect the presence of megacities, and even determine if there are rings and moons encircling the world. Even better, this will work for planets that are too close to their star to easily be observed by telescopes.
Ground based radar observations of cloud-shrouded Venus in the 1970s (shown above) first identified the highly radar reflective mountainous regions.
In the case of probing extrasolar planets, a super-radar would fill the gap between optical and infrared space astronomy, and an eventual interstellar mission to a target planet. And, unlike star-travel, the data could be returned within the lifetime of the experiment's builders.
PICTURES: Top 10 Places To Find Alien Life
The facility also might be good for a SETI experiment because the beam would be 25 times brighter than the sun and therefore attract the attention of extraterrestrial astronomers. The radar beam could also pick up alien artifacts such as large radio telescopes that would reflect a bright beam back to Earth like the reflective optical tape on a stop sign.