LEADVILLE, Colorado — Several 9NEWS veiwers sent in photos of a mysterious looking circle shaped cloud on Friday. It was seen by mountain residents from Aspen to Leadville.

Circle contrail
View from Crested Butte
Brandon Blomberg

The cloud is called a condensation trail or contrail, It is cause by warm exhaust from jet airplanes mixing with the cold atmosphere. It is a very high level cirrus cloud, which explains why it was seen in so many different locations. 

circle contrail
Circular jet contrail seen from Crawford, Colorado
Jason Martin

It was also fairly long-lasting. When there is more humidity in the upper air, jet contrails will last longer. There was a storm system just starting to move in Friday, that was bringing the added moisture in with it. If there is low humidity in the upper air, contrails will be short-lived, or may not even form at all. 

Circle contrai
The circle con-trail seen from Crested Butte
Callie Koch

The National Weather Service office in Grand Junction caught the contrail on satellite imagery, as a plane made a circle over the Grand Mesa. 

The likely culprit for this circular contrail was Delta Flight 442 bound for Salt Lake City from Ft. Lauderdale. The flight data shows the circle in its course. The reason for the loop is still a mystery, but planes will sometimes loop if the destination airport is busy.

Another meteorologist from the Grand Junction office added the flight data to a previous Tweet. 

Delta Flight 442
Delta Flight 442 course from Flightrader24