The Hunt for Life on Mars

As a result of NASA's Viking Project in the 1970s, scientists confirmed that the atmosphere of Mars is primarily carbon dioxide (CO2). Nitrogen, argon, and oxygen are present in small percentages, along with trace amounts of neon, xenon, and krypton. The Martian atmosphere contains only a wisp of water (about 1/1000th as much as found in Earth's atmosphere). But even this tiny amount can condense and form clouds that ride high in the Martian atmosphere or form patches of morning fog in valleys. There is also evidence that Mars had a much denser atmosphere in the past—one that was capable of permitting liquid water to flow on the planet's surface. Physical features resembling riverbeds, canyons and gorges, shorelines, and even islands hint that large rivers and maybe even small seas once existed on the Red Planet.

Among the many scientific discoveries about Mars that were made as a result of early space age exploration, exobiologists regard the possible presence of liquid water on Mars—either in its ancient past or presently preserved somewhere beneath the surface of the planet—as the most important. These scientists consider water as the key in their search for extraterrestrial life because everywhere they find water on Earth, they also find life. So, if Mars once had liquid water or still does today (in some special subsurface niche), there arises a very compelling argument that at least microscopic life could have emerged on the Red Planet.

In the mid-1990s, stimulated by the exciting possibility of life on Mars (extinct or perhaps still existing there today), NASA and other space-exploration organizations launched a variety of robot spacecraft to accomplish more-focused scientific investigations of the Red Planet. Beginning in 1996, some of these missions have proven highly successful, while others have ended as disappointing failures.

In December 2004, NASA planners published a strategic roadmap that defines the civilian space agency's space exploration objectives for the planet Mars, extending to the year 2035 and beyond. The central scientific theme of the focused exploration effort is simply "Follow the water." NASA management views sequenced exploration by a series of sophisticated robot spacecraft as paving the way for larger-scale human exploration missions.

NASA is conducting robotic exploration of Mars to search for evidence of life, to understand the history of the solar system, and to prepare the way for future missions to Mars by human explorers. After acquiring adequate knowledge about the Red Planet through versatile and progressively more-complex robot spacecraft missions, NASA plans to send the first human-crewed mission to Mars sometime around 2035. The discovery of existing microbial life on the Red Planet and concerns about planetary contamination (forward or back) could modify the schedule for human expeditions to the surface of the planet. Robot spacecraft might also discover fossil records on Mars that provide clear evidence of extinct creatures (including microbial life-forms) that once inhabited the Red Planet. This type of momentous discovery would also alter the current, multidecade exploration roadmap.

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