Work is continuing to refine and apply the system for dating Martian surface features by counting impact craters. I've been developing this system since the 1960s. It has the potential for allowing approximate dating of surfaces on all planets. We are moving toward more application to the erosion/deposition history of Mars.
A major development came at the end of 2006, when Malin et al. announced they had detected formation of small craters (~10 to 20 m in size) on Mars during the Mars Global Surveyor mission. Their measurement of detection rate agreed with the rate we have been using within about a factor two or three. This diffused recent criticisms that our crater formation numbers at those sizes are off by factors as much as 2000 (a suggestion based on studies of secondary impacts, which involved erroneous assumptions about our method.) I published a 2007 paper in Icarus on this work.
During 2007, I have been a member of the European Mars Express imaging team. A paper in Geophysical Research Letters, was prepared in 2007, confirming the shape of the small-crater size distribution used in our "isochron" system of dating, and empirically confirms earlier theoretical discussions of how the shape of that distribution can be distorted by obliteration events. This paper opens the door to better analysis of the complex erosion/deposition history of Mars.
New studies of the effects of secondary cratering and use of small craters for dating have been begun with through the International Space Science Institute (ISSI, Bern, Switzerland) with an international team including Olga Popova (Moscow), Cathy Quantin (Lyon), and Stephanie Werner (Oslo).
Currently I am working to apply these principles to the study of an extraordinary unnamed Martian crater that contains lobate glacier-like flow features and other modification. We date the crater as some 109 y old, but the topographic structures, at scales of 10-20 m, on the surface of the apparent glacier feature give ages of only some 106-107 y, supporting the view that may be associated with recent mantling and accumulation of by ice-rich dust due to climate changes driven by 10-My obliquity cycles. A partial draft paper involves collaboration with PSI researchers Dan Berman and Frank Chuang, as well as Veronique Ansan and Nicolas Mangold of Orsay, France.
Hartmann, W. K. 2007. Martian cratering 9. Toward resolution of the controversy about small craters. Icarus, 189, 274-278.
Hartmann, W. K., Cathy Quantin, Nicolas Mangold. (2007) Possible long-term decline in impact rates 2: Lunar impact-melt data regarding impact history. Icarus, 186: 11-23.
Quantin, Cathy; N. Mangold, W. K. Hartmann, P. Allemand 2007 Possible long-term decline in impact rates 1: Icarus, 186, 1-10.
Popova, Olga, William K. Hartmann, Ivan V. Nemtchinov, Derek C. Richardson, and Daniel C. Berman. (2007) Crater clusters on Mars: Shedding light on Martian ejecta launch conditions. Icarus.
Hartmann, W. K., Gerhard Neukum, and Stephanie Werner 2008. Confirmation and utilization of size-frequency distributions of impact craters produced on Mars. Geophys. Res. Lett. 35, L02205, doi:10.1029/2007GL031557.