On September 29, 2009, the Messenger spacecraft flew by the planet Mercury.  The approach data was successfully obtained, but thanks to a safe mode incident, the departure data was lost.  On October 3, the spacecraft finally recovered.  It took this image through its wide angle camera that day

Only albedo features can be seen.  Had the Narrow Angle Camera taken data that day, good imagery could have been obtained, but since it would have been of little value had closer data been taken, none were scheduled until October 10th.  In that view, shown below, a few large craters can still be seen on the terminator despite a distance of 2 million kilometers - it is still better than the image above. 

While the loss of departure imagery is disappointing, all in all the Messenger flybys proved very successful.  One can only look forward to the beginning of the orbital mission next year!

Raw Data Courtesy APL/JHU/NASA   Processed Images Copyright Ted Stryk