Greetings, E.T. (Please Don’t Murder Us.)

Greetings, E.T. (Please Don’t Murder Us.)
Writing in Scientific American, the former chairman of SETI, John Gertz, argued
that ‘‘a civilization with malign intent that is only modestly more advanced than we are might be able to annihilate Earth with ease by means of a small projectile filled with a self-replicating toxin or nano gray goo; a kinetic missile traveling at an appreciable percentage of the speed of light; or weaponry beyond our imagination.’’
With exobiology, Vakoch realized, he didn’t have to settle on one discipline: ‘‘When
you think about life outside the earth, you get to dabble in all of them.’’
As early as high school, Vakoch began thinking about how you might communicate with an organism
that had evolved on another planet, the animating question of a relatively obscure subfield of exobiology known as exosemiotics.
Your guess about each value in the Drake Equation winds up revealing a whole worldview: Perhaps you think life is rare,
but when it does emerge, intelligent life usually follows; or perhaps you think microbial life is ubiquitous throughout the cosmos, but more complex organisms almost never form.
Even if a small fraction of alien civilizations out there would be inclined to shoot a two-kilogram pellet toward us at half the speed of light, is it worth sending a message if there’s even the slightest chance
that the reply could result in the destruction of all life on earth?