Object moving very slowly with smoke or vapor trailing behind it.

Last summer in the evening my husband came in from outside and asked me to come look at something in the sky.  In the southwestern sky you could see a small object with something trailing behind it.  
At first we thought it was a flock of geese, but when we looked through binoculars we could see that it was some kind of craft with vapor or smoke coming out the back.  First thought, plane in distress, but it was moving extremely slow and kept on the same trajectory until we couldn’t see it because of the trees in our yard.  
I got in the car and drove to an open spot to see if I could spot it, again, afraid it was a plane in distress, but I could not locate it.   We watched the news that evening to see if a plane crashed, or nearly crashed had taken place, but there was no mention of anything.  It was definitely not a flock of geese, and it could not have been a meteorite as the vapor didn’t trail that far behind and it moved VERY slowly.  
We like to know if anyone else experienced this event.
Witness indicates that the date of the sighting is approximate.  PD