Could WE Probe ET With Interstellar Radar?

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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.

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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.

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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.

Electrical engineer Louis Scheffer of the Howard Hughes Medical Institute in Chevy Chase, Maryland, in a recent paper, envisions the a radar transmitter facility measuring 200 miles on a side, and containing a mosaic of over 1 trillion small antennas. The transmitter — ideally located in space — would need to suck up 10 terawatts of solar power to operate.  The transmitter would be so awesomely powerful it could be used to Death Star blast debris out of Earth orbit, or beam power to distant space probes.

A companion receiving antenna array would consists of 100,000 Arecibo antenna-sized dishes — each 1,000 feet across — spread over an area of 70 square miles. I think this would be an ideal lunar engineering project. An army of robots and lunar soil fabrication machines on the moon’s radio-quiet farside could build the array.

Such a facility, which I would call the Cyclops Radar Array (with apologies to the 1971 NASA SETI study of a mega-radio telescope with the same mythological name), would be our equivalent of building the pyramids, rather than to honor pharaohs, it would serve inquisitive scientists for centuries. Antennas could be added to the “orchard” over time to boost the range of the receiver. Eventually the Cyclops be use to communicate with our first interstellar probes.

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The price tag for such a mega-project is roughly $20 trillion. But it is significantly cheaper and far more versatile that building and launching a single ultra high velocity interstellar probe that would take centuries to finally return data — if it survived the voyage.

The Cyclops radar as described would have an effective range of 20 light-years, encompassing at least 100 stars. The primary target would be the neighboring Alpha Centauri binary system, which already has one confirmed planet, and no doubt many more. Other targets in order of distance would be Proxima Centauri, Barnard’s Star, and the newly discovered brown dwarf binary WISE J104915.57-531906.

A lingering question is that if this is such a good idea, why haven’t we already been radar scanned by nearby advanced civilizations?

Publication: “Investigating Nearby Exoplanets via Interstellar Radar,” arXiv:1301.0825 [astro-ph.IM]

Image credit: NASA, NRAO, University of Puerto Rico

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