Sometimes people like to get away from civilization, all civilization. Unfortunately, that's becoming harder and harder between the increasing population and the advancement of technology. If you go to most isolated parts of our Chihuahuan Desert, you may think, "Finally, free from civilization". But wait! What's that white streak cutting across the blue sky? Yep, a contrail—the rest of the world isn't that far away after all.
What is a contrail, anyway? Oh, you know what it looks like. A long, cloud-like, narrow white line, sometimes stretching across the whole sky. But what is it? Well, it's not only cloud-like—it is a cloud, albeit a man-made one. Clouds form when warm, water-containing gases cool to the point that the water condenses out. The resulting small water droplets reflect light, appearing white to us on the ground. Jet-propelled airplanes spew out enormous amounts of very hot gases into a very cold atmosphere. If the surrounding air isn't so dry that the water immediately evaporates again, that tell-tale sign of civilization lingers on, telling you once again, there's no escape.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.
More accurately, the water-containing gases almost immediately produce particles of ice, rather than droplets of liquid water.