While the U.S. National Aeronautics and Space Administration's (NASA) human-manned space-travel efforts have stalled in recent years, the agency has enjoyed a relatively strong string of successes with unmanned exploration of Mars.
I. Take me to the River
The latest in a string of robotic explorers has achieved an important milestone -- NASA's Curiosity rover has observed first had one of the dried up stream beds that NASA scientists long speculated existed.
While past NASA rovers had found signs of water, they did not observe a definitive streambed -- until now.
By imaging the pebbles in the streambed, which were smoothed by the current and cemented into conglomerate rocks, researchers were able to derive in startling detail how the Martian stream likely looked.
University of California, Berkley professor and Curiosity science co-investigator William Dietrich elaborates, "From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep. Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."
II. An Odd Location
The streambed lies within the floor of the Gale Crater, in which Curiosity is currently puttering about. The rover's find lies on the north rim, the deepest part of the unusual crater; with elevation reach over 4,000 ft. below Martian "sea level" (defined as the average elevation around the equator).
What makes the crater so unusual -- and a key reason why NASA landed Curiosity nearby -- is the presence of a massive mountain at the crater's center, named Mount Sharp (formally Aeolis Mons). Mount Sharp is 5.5 km (18,000 ft.) high -- make it three times as tall as the Grand Canyon is deep.
Most craters are created by collisions with extraplanetary objects. But the presence of the inner mountain suggests some sort of erosion process gave birth to the crater, making a promising target for water.
And indeed, stretching down the northern rim towards the central mountain was a streambed. Images indicate that a channel named Peace Vallis brought water from outside the crater into a so-called "alluvial-fan" -- a fan shape arrangement of smaller streams. NASA said the presence of the fan indicates the stream was active for a long period of time.
Rebecca Williams a researcher at the Planetary Science Institute in Tucson, Arizona and member of the Curiosity team, comments, "The shapes tell you they were transported and the sizes tell you they couldn't be transported by wind. They were transported by water flow."
III. Rover Prepares to Dig for Water, Organics
The success comes after the NASA rover used its telephoto camera to examine a couple of outcroppings -- "Hottah" and "Link" during the first 40 days of its mission. Remarks Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology (CalTech) in Pasadena, Calif., "Hottah looks like someone jack-hammered up a slab of city sidewalk, but it's really a tilted block of an ancient streambed."
Now the rover gets to use its 10 instruments to try to examine the chemical composition of the sediment that binds the pebbles together. The rover is equipped with four spectrometers, including an alpha particle X-ray spectrometer (APXS) and an X-ray powder diffraction and fluorescence module dubbed Chemical and Mineralogy (CheMin).
The best may yet lie ahead for the rover, though. It is equipped with Dynamic Albedo of Neutrons (DAN) device to try to spot hydrogen or ice/water at the surface of the streambed. Researchers also hope to possibly find carbon-rich organic molecules on the lower slopes of the mountain.
Images showed the mountain to be rich in sulfate and clay deposits, which researchers hypothesize could preserve organic molecules in the harsh Martin climate. Potential organics will be examined with the Sample Analysis at Mars (SAM) package, which consists of a Quadruple Mass Spectrometer (QMS) and a gas chromatograph (GC).
Prof. Grotzinger hints at his team's hope of discovering signs of life, commenting, "A long-flowing stream can be a habitable environment. It is not our top choice as an environment for preservation of organics, though. We're still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment."
The discovery is also useful as it offers evidence reaffirming the long-held notion that Mars could be made habitable/semi-habitable if its ice caps were melted and its atmosphere rebuilt.
IV. A Third Generation Design
The Curiosity mission was preceded by the 2003 Mars Exploration Rover Mission (MER) -- a mission which featured the six-wheeled solar-powered robots Spirit and Opportunity. The 1997 Mars Pathfinder and its Sojourner rover, a far tinier six-wheeled solar-powered design, preceded that mission. Sojourner was the first rover to operate on Mars.
Curiosity is bigger than the mid-size MER rovers and the tiny Sojourner rover. NASA used the lessons learned from its predecessors' malfunctions, along with modern electronics to produce a more rugged, robust, and function design, the third time around.
NASA first reached Martian orbit with the Mariner probes in the mid-1960s, as did the Soviets with their Mars series of fly-by probes. The first spacecraft to land on Mars was NASA's 1975 Viking lander.
It took Curiosity just under 9 months to reach the red planet, slightly longer than its predecessor MER, which took seven months. Reaching the red planet isn't cheap, despite NASA's experience.
The Pathfinder mission cost around $150M USD, the MER cost roughly $950M USD of which roughly eight-ninths went towards the construction, launch, with the remainder going towards operating the twin rovers. Curiosity was even more of a pricier beast. NASA spent $2.5B USD, struggling with cost overruns before it finally launched the ambitious design to the skies.
Source: JPL
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