Berlin, September 24 : The High Resolution Imaging Science Experiment (HiRISE), carried by NASA's Mars Reconnaissance Orbiter is helping scientists make leaps forward in understanding both the ongoing and ancient processes that shaped the surface of Mars.
A study of the nature and distribution of ancient megabreccia, led by Professor Alfred McEwen, HiRISE's Principal Investigator, suggests that this bedrock was formed during the late heavy bombardment period.
Megabreccia consists of angular, randomly-orientated blocks that formed suddenly in energetic events such as meteorite impacts. It is thought to contain fragments of the oldest and deepest bedrock exposed on the surface of Mars.
According to McEwen, "We think that the megabreccia was formed during a period of heightened meteorite activity about 3.9 billion years ago. This is around the time life appears to have begun on Earth, but we have very little record of that era in our terrestrial geology because ancient rocks are heavily metamorphosed."
"Mars preserves a much better record of the heavy bombardment and, unlike the dry lunar surface, it shows the environmental effects in a water-rich crust," he added.
The HiRISE team has identified megabreccia in more than 50 locations consistent with the most ancient terrains on Mars. These include the central uplifts of large craters and deep exposures such as the floor of parts of Valles Marineris.
Well-exposed rock outcrops are needed to identify megabreccia, in particular from the diversity of colours and textures indicating diverse rock types.
Megabreccia contains rock fragments from the earliest geological period on Mars, the Noachian era, which is more than 3.8 billion years ago.
The megabreccia blocks vary in size from relatively small (1-5 metres) to larger than 10 metres in diameter.
The small blocks were probably formed by post Noachian cratering, particularly when found in material filling crater floors. The large blocks are only found in locations consistent with hard, deep bedrock, such as the central uplifts.
McEwen suggests that the blocks are largely cemented by melt from impacts and hydrothermal alteration.
"We are in the midst of a paradigm shift in understanding the Noachian crust of Mars, thanks to the high-resolution data from the Mars Express and MRO missions," said McEwen.
"The spectrometers on these missions found evidence of alteration due to water in the bedrock in many, if not most Noachian aged places. However, the younger Noachian era may have been relatively dry, so we may need to study the oldest outcrops of megabreccia to understand this era," he added.
McEwen will also be presenting results of processes that may be shaping the surface of Mars today.