Interstellar Semaphores?

This article by Luc Arnold (2005) explores light curves from aspherical transiting objects – namely a triangle, two screen, and a six screen. By analyzing the resultant light curve and its deviation from a standard light curve (due to a spherical object), it argues  that these can be potential signatures of Extra Terrestrial Intelligence (ETI) and even as a means of interstellar communication .

Louver like six screen object

Arnold first establishes the premise for the detectability by space based telescopes of such irregular shaped objects (shown above), and then the ability to distinguish these asymmetric shapes from spherical planets. He then considers not one such object, but a series of objects of different sizes and spacing (gaps). These objects could encode a pattern (say prime numbers) to be used as a means of transmitting information. This is reminiscent of late 18th century communication during the Anglo – Franco wars using optical telegraphs and semaphores (as shown below).

Here, they used various ON and OFF positions of the shutter to transfer 6 bits of information – 2^6 – 1 = 63.


Murray’s 6 shutter telegraph 


A similar concept is hypothesized by Arnold, as a means of interstellar information transfer. The variations in the light curve will be akin to the shutters in the telegraph changing state. He then compares the data transfer rate per steradian of this method with that of laser beacons. Though they have a higher transfer rate if focussed on one star due to their small cone angle, if one aims to transmit over a greater area, then the interstellar semaphores are faster.

I think it is a very novel method for communication that has parallels with techniques used by humanity a few centuries ago. Further, using this technique we may communicate with civilizations which are not in the Earth Transit Zone by giant sails and solar panels in polar orbits of the Sun, perhaps a viable alternative to energy intensive beamed transmission?