The Scale of a Martian Hydrothermal System Explored through the Nakhla Martian Meteorite

Neutron and X-ray tomography show that the meteorite had limited exposure to water. Credit: Josefin Martell, Lund University, Sweden.

The presence of water on Mars has been crucial in determining whether or not life might have existed there. The Viking Landers in the 1970s first detected the presence of phyllosilicates, which are hydrous minerals, on Mars. Since then, hydrous phases on Mars have been detected by rovers and remote sensing instruments and also in martian meteorites. However, until a Mars sample-return (MSR) mission succeeds, detailed laboratory studies of such hydrous phases remain limited to those in the martian meteorites. Nakhlite meteorites are martian igneous (of volcanic origin) rocks and are rich in pyroxene and olivine (originally anhydrous phases) that show evidence of having been aqueously altered about 630 million years ago. This aqueous alteration on Mars is believed to be associated with hydrothermal systems that might provide microhabitats. Understanding the extent and duration of hydrothermal systems on Mars is crucial to determining whether they might have supported life.

A research team led by Josefin Martell of Lund University in Sweden has investigated the three-dimensional distribution of hydrous phases within the Nakhla meteorite using neutron and X-ray tomography to determine whether hydrothermal alteration is pervasive. Neutron tomography is sensitive to light elements such as hydrogen, allowing it to detect the location of hydrogen atoms and thus track the effects of hydrothermal alteration. Results of this work show that clusters of hydrous phases called iddingsite within and around olivine grains are restricted to discrete volumes and are not likely part of wider and interconnected fractures. The lack of interconnectivity suggests that hydrothermal alteration was localized within the Nakhla meteorite, involving only small volumes of fluid. This implies that the alteration of the Nakhla source region on Mars was not caused by large-scale hydrothermal systems. Consequently, the hydrothermal systems were most likely short-lived, meaning the martian subsurface sampled by Nakhlite meteorites could not have provided habitable environments. READ MORE