Accessing the Martian deep subsurface to search for life

To date there have been no data indicating that the surface of Mars is inha bited. Research conducted on Earth has revealed that life can exist deep be neath the surface of a planet. Current data from Mars missions suggesting t he presence of liquid water early in Mars' history and mathematical modelin g of the fate of water on Mars imply that liquid water may exist deep benea th the surface of Mars. The existence of liquid water beneath the Martian s urface, combined with life's ability to live chemolithoautotrophically, lea ds to the hypothesis that life may exist deep beneath the Martian surface. Acquisition and analyses of Martian subsurface samples will shed light on t he possibility of extant or extinct life, in permafrost and liquid water, o n Mars, the processes leading to the origin of life, and the size of the So lar System's habitable zone. The results of a workshop convened by NASA in 1998 suggest that no fewer than two missions could be considered for access ing the deep subsurface of Mars. This two mission scenario includes a missi on penetrating to a depth of similar to 300 m and a mission penetrating to a depth of similar to 3 km. As in all space missions the power, mass and vo lume of the penetration system and all associated equipment to be used to g ain access to the Martian subsurface must be kept to a minimum. One techniq ue that may be applicable, but in need of further development, is an electr ically heated probe (bit) that penetrates and cores by melting through rock . The probe is attached to an umbilical cable to provide power and to allow periodic retrieval of the probe. This approach appears to address planetar y protection concerns and may decrease the mass, power and volume requireme nts of conventional drilling systems by eliminating the need for casing mat erial, drilling fluids, and handling potentially contaminated debris from t he bore hole. Deep drilling on Mars presents several planetary protection f orward and back contamination issues. These issues include sample handling at the surface as well as upon return to Earth. (C) 2000 Elsevier Science L td. All rights reserved.