A Sonic Boom
The plane was an F/A-18 Hornet assigned to Strike Fighter Squadron One Five One (VFA-151). It was photographed over the Pacific on July 7, 1999 by Ensign John Gay.
Cones of condensation around planes are a fairly common phenomenon. They're formed when there is a combination of the right amount of humidity and enough aerodynamic pressure. A plane does not have to be breaking the sound barrier for a cone to form, but in this case the plane reportedly was about to do so.
The photo began circulating after it was featured on the Astronomy Picture of the Day site.
Links and References
• A Sonic Boom, Astronomy Picture of the Day.
Photo Categories: Real But Suspected Of Being Fake,