Because resurfacing ages were derived from crater statistics, these secondary ages were used to define the unit age rather than the base age.Using the methods described herein, we modelled ages that are consistent with the interpreted stratigraphy." and of particular interest to some recent claims of young ages with great accuracy (e.g 5 /- 2 My) for quite small areas - "William Bottke of the Southwest Research Institute in Boulder, Colorado, US, who is an expert on the dynamics of the asteroid belt, also concludes that small craters are predominantly secondaries.He says there are just not enough small objects in the asteroid belt to account for the observed rates of small impacts on Mars.A surprising feature of ALH 84001 has been its extremely ancient age, 4.50 billion years, as determined by samarium-neodymium (Sm-Nd) and rubidium-strontium (Rb-Sr) isotopic dating.If correct, the ancient age implies that the magma in which ALH 84001 formed intruded the primordial crust, perhaps forming in a deep ocean of magma that surrounded Mars during its initial differentiation into metallic core, rocky mantle, and primary crust.
Equally important to many cosmochemists, the meteorite also contains important information about the construction of the Martian crust by magmas derived from the interior, and the subsequent modification of those igneous rocks by large impacts and circulating water.The new, post-Viking generation of Mars orbital imaging and topographical data provide significant higher-resolution details of surface morphologies, which induced a new effort to photo-geologically map the surface of Mars at ,000,000 scale.Although from unit superposition relations a relative stratigraphical framework can be compiled, it was the ambition of this mapping project to provide absolute unit age constraints through crater statistics.In this study, the crater counting method is described in detail, starting with the selection of image data, type locations (both from the mapper’s and crater counter’s perspectives) and the identification of impact craters.We describe the criteria used to validate and analyse measured crater populations, and to derive and interpret crater model ages."Small craters may not be telling you much," Bottke says.As people all around Earth partied and watched fireworks signal the launch of 2017, some 45 million miles away the New Year got off to a start that was unprecedented in every good way: the Mars Exploration Rover (MER) mission completed its 13. “I don't think anyone in 2004 thought that we'd be commanding this bad girl in 2017,” said MER Deputy Principal Investigator Ray Arvidson of Washington University St. “It's just truly amazing.” And Opportunity is not slowing down.Reference: t the risk of revealing my deep-seated biases, I have to say that ALH 84001, whether it ever teemed with microorganisms or not, is one great igneous rock.And igneous rocks are wondrous products that reveal the composition of planetary interiors, the processes that operated in magmas as they migrated to the crust, and how the magmas crystallized far beneath the surface or in lava flows that erupted onto it, shaping the landscape. And thin sections of them look great in a polarizing microscope.In fact, this robot field geologist is on her way to an ancient gully and traversing now some of the most treacherous terrain she has ever encountered to get to what just may be most significant research site the mission will visit on its quest to “Follow the Water” and find evidence for past environments that once may have been inhabitable.“This gully has been calling us for years now,” said MER Principal Investigator, Steve Squyres, of Cornell University.