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Exploration by Martian Landers

• Seven U.S. spacecraft have successfully landed on the Martian surface, conducting detailed geological and chemical analyses of Martian surface rocks, and searching for life and water.- Based on data from studies of it, a group of scientists pointed to spherical structures like those produced by bacteria on Earth, the presence of chemical compounds sometimes associated with Earth biology, and curved, rod-like structures resembling Earth bacteria, which the researchers interpreted as fossils of primitive Martian organisms.- The Curiosity rover landed to study Mars' climate and geology, investigate water's past and present roles, determine if the landing site (with in Gale Crater) was ever favorable for microbial life, and assess the planet's suitability for future human exploration.- In 1997, the Mars Pathfinder lander measured the Martian atmosphere and atmospheric dust, while its Sojourner rover performed chemical analyses of soil and rocks.- The Spirit landing site was rocky, similar to terrain encountered by previous landers, though close study revealed that most rocks in the lander's vicinity appeared to have been significantly altered by water long ago.- The Gas Exchange experiment provided a nutrient solution to any residents in a Martian soil sample and looked for gases indicating metabolic activity.

Exploration by Martian Landers

• Seven U.S. spacecraft have successfully landed on the Martian surface, conducting detailed geological and chemical analyses of Martian surface rocks, and searching for life and water.


• Both U.S. Viking missions sent landers to a desolate, wind-swept plain near the Martian equator just east of Tharsis, scattered with rocks of all sizes. The Viking landers performed several chemical analyses of surface rocks and conducted experiments designed to test for life. One important result was the high iron content in the planet's crust.


• Chemical reactions between the iron-rich surface soil and oxygen in the atmosphere are responsible for the iron oxide (rust) that gives Mars its distinctive red color.


• In 1997, the Mars Pathfinder lander measured the Martian atmosphere and atmospheric dust, while its Sojourner rover performed chemical analyses of soil and rocks. It revealed chemical compositions different from those in Martian meteorites found on Earth.


• The Pathfinder landing site was chosen to be near the mouth of an outflow channel, and the characteristics of many rocks surrounding the lander were consistent with the idea they had been deposited there by floodwaters.


• In 2004, the twin Mars Exploration Rovers, Spirit and Opportunity, reached their targets on opposite sides of the planet and conducted chemical and geological studies of the rocks they encountered. Their search for evidence of liquid water on ancient Mars provided strong evidence for ancient standing water, changing the minds of many skeptical scientists.


• The Spirit landing site was rocky, similar to terrain encountered by previous landers, though close study revealed that most rocks in the lander's vicinity appeared to have been significantly altered by water long ago.


• Opportunity found itself surrounded by rocks that showed every chemical and geological indication of having been very wet, and possibly submerged in briny water, in the distant past. The rocks near Opportunity's landing site appear to have been alternately underwater and dry for long periods of time, perhaps as a shallow lake that alternately filled and evaporated many times over Mars' history.


• The Phoenix mission landed in late autumn in the planet's north polar region. During its final weeks, its sensors reported the first snowfall as winter approached. It confirmed the presence of water ice beneath the surface at the landing site and found clay and carbonates in the soil, both indicators of a past wet environment. The mission ended when diminishing sunlight and extremely low temperatures shut down the lander's power supply.


• The Curiosity rover landed to study Mars' climate and geology, investigate water's past and present roles, determine if the landing site (with in Gale Crater) was ever favorable for microbial life, and assess the planet's suitability for future human exploration.


• Curiosity landed in an area believed to have been an ancient streambed. Its analysis revealed complex chemistry within the Martian soil, including minerals containing what are thought to be life's basic building blocks carbon, hydrogen, oxygen, phosphorus, sulfur, and chlorine. The origin of these minerals biological or non-biological remains unclear.


• By analyzing the soil's salinity, the rover found the environment may have been habitable billions of years ago. Curiosity also measured a rise in atmospheric methane in its vicinity. Since living things, as we know them, can produce methane, its discovery supports the idea that life may have once existed there.


• Martian soil contains significant amounts of water and carbon dioxide.


• In 2014, samples from a rock called Cumberland provided the first definitive detection of organic molecules on the Martian surface.
  Life on Mars?


• Scientists knew there were no extensive canal systems, no surface water, almost no atmospheric oxygen, and no seasonal vegetation changes. The current lack of liquid water on Mars makes the chances of life there now particularly low. However, flowing water and a possibly thicker atmosphere in the past may have created conditions for life to emerge long ago.


• The Viking landers conducted experiments designed to detect current biological activity. All three Viking biology experiments assumed some basic similarity between hypothetical Martian bacteria and those on Earth.


• The Gas Exchange experiment provided a nutrient solution to any residents in a Martian soil sample and looked for gases indicating metabolic activity.


• Another experiment added compounds with radioactive carbon to the soil and waited for results suggesting Martian organisms had eaten or inhaled this carbon.


• Finally, the Labeled Release experiment added radioactively tagged carbon dioxide to a soil and Martian atmosphere sample, waited, then removed the gas and tested the soil (by heating it) for signs that something had absorbed the tagged gas.


• Initially, all three experiments seemed to give positive signals! However, studies showed all results could be explained by inorganic (non-living) chemical reactions. Thus, we have no evidence of even microbial life on the Martian surface.


• The Viking robots detected odd reactions that mimicked basic chemistry of living things, but they didn't detect life itself.


• If bacterial life did arise on an early, Earth-like Mars, we might find its fossilized remains preserved on or near the Martian surface.


• One alternative place to search for evidence of life on Mars is here on Earth. ALH84001, a 2 kg black meteorite, was found in Antarctica. Chemical analysis indicates it originated on Mars. It was blasted off that planet long ago by some kind of meteorite impact.


• Based on data from studies of it, a group of scientists pointed to spherical structures like those produced by bacteria on Earth, the presence of chemical compounds sometimes associated with Earth biology, and curved, rod-like structures resembling Earth bacteria, which the researchers interpreted as fossils of primitive Martian organisms.


• The team released an analysis of a second meteorite, also believed to be from Mars, and again reported evidence for microbial life with a size, shape, and arrangement similar to known nanobacteria cells on Earth.


• Some scientists maintain that all evidence could be due to chemical reactions that don't require any biology. Many key experiments have yet to be conducted, like testing the suspected fossils for evidence of cell walls or any internal cavities. No one has found any amino acids, the building blocks of life as we know it.


• Most people in the field have concluded that the findings, in their totality, don't support the claim of ancient life on Mars.