Selections from 2018: Using Lasers to Talk to ET


Editor’s note: In these last two weeks of 2018, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Optical Detection of Lasers with Near-Term Technology at Interstellar Distances

Published November 2018

Main takeaway:

Could we communicate with distant extraterrestrial intelligence using lasers? Two scientists from the Massachusetts Institute of Technology, James Clark and Kerri Cahoy, have determined that we could produce a detectable laser signal out to 20,000 light-years using current or near-term technology.

Why it’s interesting:

The challenges of communicating with hypothesized life beyond our solar system are numerous. One of the most fundamental questions is whether we are technologically capable of producing a strong signal that could be easily detected at large distances. In their feasibility study, Clark and Cahoy show that we can — and, moreover, that such a signal could have a broad enough beam that we could target nearby exoplanets with uncertain orbits (like the planet Proxima Centauri b) or the entire habitable zones of more distant systems (like the TRAPPIST-1 system).

Other challenges to communication:

European Extremely Large Telescope

The European Extremely Large Telescope, a proposed upcoming telescope with a 39-meter mirror. A telescope of this size could be used to focus a megawatt laser to communicate with distant intelligence. [Swinburne Astronomy Productions/ESO]

To be spotted by a hypothetical civilization orbiting a distant star, our communicating laser beam must be bright enough to stand out above the background light of our own star, the Sun. If this is possible — which Clark and Cahoy suggest would be with a megawatt-class laser focused by a telescope of tens of meters in diameter — then we still run up against low odds of an actual conversation within human lifetimes due to the long time it would likely take to send and receive signals. Nonetheless, it would be a good start!


James R. Clark and Kerri Cahoy 2018 ApJ 867 97. doi:10.3847/1538-4357/aae380