There are thousands of known exoplanets, but we can only detect a small fraction of planets in the cosmos. Currently, the bright light of stars blots out the meager light from exoplanets, and aliens looking our way would have a similar problem. A study from MIT’s Department of Aeronautics and Astronautics suggests Earth could make itself more visible to invite alien contact. All we’d need is a giant laser and an even bigger telescope.
The paper, which has been published in the Astrophysical Journal, is not a full plan for how to build the necessary apparatus. Instead, it’s more of a “feasibility study,” according to MIT graduate student and author James Clark. We would need a 1 or 2-megawatt laser, with is powerful but not unprecedented. In the laboratory, scientists have created lasers in the petawatt range. Simply shining that laser upward isn’t going to get the job done, though. Clark’s study also calls for the laser to be focused through a giant 30 to 45-meter telescope.
An energy emission on this scale should overcome the brightness of the sun, giving Earth a “porch light” to attract attention from other star systems. The signal should be easy to detect from as far away as 20,000 light years. Of course, it would take 20,000 years for the signal to get out there. The laser would be even more noticeable in closer star systems like Proxima Centauri and TRAPPIST-1, which are about three and 40 light years away respectively.
Theoretically, another civilization could spot our laser signal with a small 1-meter telescope. They could use a smaller laser to reply if it were pointed directly at Earth. By modulating the intensity of the light, we could exchange simple messages in binary with a data rate of a few hundred bits per second. It would take years for the message to get to another solar system and at least as long to receive a reply.
The megawatt laser is workable — the US military experimented with megawatt-scale systems on jets to shoot down missiles. The 30-meter telescope would be much larger than any we currently have as the trend is toward building multiple smaller observatories. It should be possible to build one, though. Clark also suggests building the apparatus atop a mountain where it would encounter less atmosphere before reaching space. The beam from such a laser would be dangerous, but the risks would be minimized if it’s locked into a skyward orientation.
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