Some of the Martian impact craters imaged by the UA's HiRISE camera on the Mars Reconnaissance Orbiter were formed in the last 10 years or less.
The HiRISE team met in Tucson the past two days and some of the discussion centered on recognition of craters that were not present in images dating back 10 years, meaning the impacts occurred sometime in the past decade.
It sounds like the planetary scientists are surprised by the number and size of new craters discovered.
[right, HiRISE image released Jan. 21, showing a small very fresh crater (roughly 300 meters across) in the image center with dark ejecta. It was probably formed by the impact of a small asteroid less than 20 m in diameter. This is not necessarily one of the craters formed in the past few years.]