In addition, Thomas Gold has conjectured that life may begin deep below the surface. The search for extant life on Mars should begin with a thorough global examination of possible ecological niches. Of particular concern is the distribution of water. As much as 500 meters of rock and soil may isolate Martian ground ice near the equator from the atmosphere. Accurate instruments are not yet available for measuring the depth and horizontal distribution of water.
Orbiters can detect seasonal changes in permafrost-induced ground patterns.
A radar altimeter of a wavelength which can penetrate the surface is a good indicator of subsurface changes and could be flown on an early mission. In the past, radar has located subterranean water formations in the Sahara. Information derived from many sources will help locate the most suitable sites. But careful site selection is crucial to reduce the number of future rover missions. A Call for Caution Even if a suitable site and a method of safely returning a sample to Earth is found, another problem remains to be solved.