in the martian meteorite, ALH 84001—prompted the federal government to devote greater resources to NASA’s Mars Exploration Program.4
The failure in 1999 of both of NASA’s next two Mars missions—Mars Polar Lander and Mars Climate Orbiter—led to major revisions in the Mars Exploration Program and to the abandonment of many aspects of the faster-cheaper-better philosophy.5 Despite the two failures, scientific interest in Mars did not wane; nor did political and financial support for a robust program of Mars Exploration. The lander mission planned for launch in 2001 was canceled, but the 2001 orbiter mission, Mars Odyssey, proceeded on schedule and has, subsequently, provided much valuable scientific data concerning Mars’s global geochemistry.
Interest in Mars exploration is not confined to NASA. In 1998, Japan’s Institute for Space and Astronautical Science launched Nozomi, a small orbiter designed to focus on studies of Mars’s upper atmosphere and interactions with the solar wind. Unfortunately, this spacecraft suffered multiple failures and was unable to enter orbit around Mars. In 2003, the European Space Agency launched Mars Express and NASA launched the twin Mars Exploration Rovers. Finally, in August 2005 NASA launched the Mars Reconnaissance Orbiter, and this spacecraft successfully entered orbit around Mars in March 2006. As a result of this unprecedented level of activity, there are currently six operating spacecraft on or in orbit about Mars.
The resilience of the Mars Exploration Rovers, Spirit and Opportunity, and the wealth of data that they and their companion spacecraft have gathered on Mars, are opening a new chapter in understanding of the Red Planet. Discoveries of stratigraphic layers, evaporite deposits, and mineral forms show clearly that Mars experienced a somewhat Earth-like warmer and wetter era.6,7 Questions remain as to how this era came to be and how Mars changed to its current cold and dry climate. Another significant set of results from Mars concerns the putative spectroscopic detection of methane in the planet’s atmosphere by ground-based telescopes8,9 and the Mars Express spacecraft.10 Although the result obtained from Mars Express is still somewhat controversial, all three sets of observations indicate methane at concentrations of about 10 parts per billion. This is significant in that methane is unstable in the martian atmosphere and would disappear in ~300 years if not replenished. Although the origin of the methane has not yet been determined, possible sources include volcanic activity, chemical reactions between water and iron-bearing minerals in a hydrothermal system, and biological activity.11
These and other recent advances are not the only factors influencing NASA’s Mars Exploration Program. Other factors include the following:
The development of a highly effective, community-based group, the Mars Exploration Program Analysis Group (MEPAG), which devised a comprehensive series of Mars exploration goals and priorities and has drafted topical reports on specific Mars exploration opportunities;12
The publication in 2003 of the NRC’s first solar system exploration (SSE) decadal survey report, New Frontiers in the Solar System: An Integrated Exploration Strategy,13 which places the exploration of Mars in the context of other SSE activities and also provides specific recommendations and priorities for a variety of Mars exploration activities;
The enunciation on January 14, 2004, of the Vision for Space Exploration, President Bush’s overarching plan for “a sustained and affordable human and robotic program to explore the solar system and beyond”;14 and
Changes in the Mars Exploration Program’s budgetary expectations for fiscal years 2006 and 2007, which resulted in various programmatic adjustments, including the cancellation of the planned 2009 launch of the Mars Telecommunications Orbiter, the loss of several Mars Scout missions in the post-2011 period, the termination of a series of robotic human-precursor missions, and the deletion of a variety of technology-development activities.15
These factors and, in particular, the last, compelled NASA’s Science Mission Directorate to revisit the sequence of missions the agency plans to launch to Mars in the period 2007-2016. After several months of study, consideration and incorporation of the guidance from NRC studies and the Vision for Space Exploration, and community consultations via individual inputs and a MEPAG-sponsored working group, the Jet Propulsion Laboratory’s Mars Advanced Planning Group developed a revised program architecture for the coming decade of Mars robotic exploration. This architecture is embodied in the report Mars Exploration Strategy 2007-2016.16