Several variations of this image were transmitted to Telstar Logistics within the last week, so we'll take that as an indication of demand and go with the flow...
What's going on in this fabulous picture? The image shows a US Navy F-18 traveling at supersonic speed in humid air at or near sea level. It is not (as one of our Associates wondered) a Photoshopped fake. Here's another photo of a different F-18 experiencing the same phenomenon:
The fluffy cloud around the aircraft is a cone of vapor created as the jet approaches or exceeds the speed of sound. The Astronomy Picture of the Day website explains how the vapor cone is formed:
When an airplane travels at a speed faster than sound, density waves of sound emitted by the plane cannot precede the plane, and so accumulate in a cone behind the plane. When this shock wave passes, a listener hears all at once the sound emitted over a longer period: a sonic boom. As a plane accelerates to just break the sound barrier, however, an unusual cloud might form. The origin of this cloud is still debated. A leading theory is that a drop in air pressure at the plane described by the Prandtl-Glauert Singularity occurs so that moist air condenses there to form water droplets.
Frankly, they had us at "Prandtl-Glauert Singularity." But perhaps you get the idea: The sound waves produced by the speeding jet generate sufficient pressure and temperature change to create instantaneous clouds of water condensation. (Vapor cones can also occur at subsonic speeds, but the higher pressures created by supersonic flight make the effect more likely.) This remarkable video of an F-14 Tomcat demonstrates what the effect looks like in slow-motion:
Still curious? Follow the links below to continue your self-guided study.
Breaking the Sound Barrier and Vapor Cones around Jets (Excellent collection of resources on the topic)
Prandtl-Glauert Singularity (Wikipedia entry)
Condensation Due to the Prandtl-Glauert Singularity (Useful summary with lots of photo links)
B1-B Breaking the Sound Barrier (Photo of an Air Force Bomber generating a vapor cone)
F-18 Goes Supersonic (YouTube video of the sonic boom cloud)