Understanding geological process on Earth is fundamental to understanding those on most other planetary bodies. Equally, geological studies on other planets where physical conditions such gravity and atmospheric pressure (or lack of it) may be different, provide testing grounds for physical models of processes that occur on Earth. This is particularly true of Mars where many processes familiar to Earth-based geologists have moulded its surface. Mary Chapman, a US Geological Survey-based scientist, is therefore to be congratulated on conceiving and bringing together this book of chapters on geological processes common to Earth and Mars.
The book is timely. After a long time gap between the NASA Viking mission that arrived at Mars in 1976, we are now embarking on a comprehensive programme of investigation of the Red Planet. Viking had the task of putting two spacecraft in orbit round the planet to make surface observations, and put two landers on the surface in an attempt to look for life. Large though this database is, it was all there was to work on for those involved in Martian studies. Now we have data from new orbital missions from both NASA and the European Space Agency, together with highly successful NASA landers, capable of roving across the surface to investigate the geology.
The first chapter sets the Martian scene with some of the latest discoveries on the surface geology from these recent missions, and identifying questions for the future. A chapter on impact craters comes next, and although most of Earth's craters have been eroded and do not show pristine surfaces, here we have the opportunity to examine them from those in almost perfect condition like Meteor Crater in Arizona, to those that are deeply dissected exposing their internal structures.
Volcanism takes up six chapters. Mars has some huge volcanoes each of which has a summit caldera complex: observations of terrestrial volcanoes are introduced to attempt to interpret those of Mars. The New Mexico (USA) volcanic field is rich in volcanic landforms and provides many analogues that provide a basis for understanding Martian volcanism, and flood lavas on Earth also provide clues to mechanisms of emplacement of flows often much larger than those on Earth. Finally, on the volcanic front, do rootless volcanic cones in Iceland have analogues on Mars?
Six chapters discuss analogues of aeolian-, lacustrine- and gravity-induced processes. Sand dunes and deposits in the western United States are seen in relation to Mars. Greenland, with its periglacial conditions, is seen as a suitable location for interpretation of Martian hillslope debris flows. Two chapters cover fluvial erosion comparing those of Mars with valleys and cataclysmic flood channels on Earth; and a third chapter considers terrestrial playa as possible analogues for some Martian surface features.
In further chapters, meteorites are used to identify Martian rock compositions, and the Canyonlands (USA) provide analogues for graben. The search for life on Mars is still high on the scientific agenda and lakes in the high Andes have been studied in an astrobiological context. Finally, the importance of analogue studies for planetary exploration by humans and robots is emphasized. A thought-provoking book – highly recommended.
