Sunday, April 22, 2012

Mars Science Laboratory

Mars Science Laboratory (MSL) is a NASA mission to Mars, whose goal is to search for organic material and microbial life on the Martian surface. To do this, the mission landed the rover Curiosity on Mars, whence it will navigate the surface and conduct scientific experiments.

The spacecraft successfully launched from Cape Canaveral, Florida on November 26, 2011. After leaving the Earth's atmosphere, it began a cruise stage that lasted until MSL approaches Mars in the summer of 2012. It successfully landed on the red planet on August 6, 2012.

This mission makes use of innovative technologies essential for any future landings on Mars. At over 2000 pounds, Curiosity is by far the largest Mars rover ever to be constructed, five times the size of the rovers Spirit and Opportunity of the early 2000's. In order to land intact on the Martian surface, a precision landing was necessary.

Previous rovers used inflatable airbags to cushion their landings, and simply bounced until settling to their destination. This did not allow high precision in landing. However, Curiosity is too large for such techniques, and made use of a more complicated landing sequence.

The landing procedure that was used to lower the Curiosity rover to the surface (click to enlarge). In the atmosphere, parachutes and braking thrusts were used to decelerate the craft. Then, a device known as a  sky crane lowered the rover to the ground on cables to ensure proper orientation.  Once Curiosity was safely on the surface, the crane detached and propelled itself away, as to not interfere with the rover.

After the landing, the first images sent back from Curiosity confirmed its position.

One of the first images from Curiosity showing the Martian surface. The venue from which the rover explored its environment was Gale Crater. This crater was selected due to the exposed sediment along its banks, which hold millions of years of Martian geologic history.

Over the next few days, the rover, remaining stationary, tested its scientific equipment, checking all of its instruments and cameras in preparation for its first motorized movement on the surface of Mars, which occurred on August 29.

On August 19, Curiosity performed its first sample analysis, using its on-board laser and spectral analyzer to determine its composition. In the following months, the rover conducted numerous experiments involving samples, both of soil and of atmosphere. In early November 2012, the atmosphere was found to contain an unusual concentration of heavy isotopes of its constituent elements (mainly carbon and oxygen, forming CO2. This indicates that the lighter isotopes were lost to space in the distant past, and this could explain the thinness of the Martian atmosphere.

During the first few months of the mission, the rover also took weather data, identifying some meteorological events on Mars. Most changes were related to dust storms and whirlwinds, and in fact the dust was discovered to catalyze a convective process in the Martian atmosphere: the dust on the side of Mars facing the Sun is lifted by wind into the atmosphere where it warms it, causing a greater differential in temperature between one half of the Martian atmosphere and the other (where it is night). This causes a flow of air from the cool to the warm side, restarting the process.

In January 2013, Curiosity imaged rocks at night, illuminating them with lights on the spacecraft. Using ultraviolet lamps, the rover searched for fluorescent minerals during the Martian night, at which time they would be visible (see image below).

In early February 2013, the rover completed its first drilling, obtaining a sample from several inches below the surface of bedrock. After obtaining a good number of rock samples and performing numerous other tests at Gale Crater, the rover prepared in June to begin a journey to its next destination, Mount Sharp. By the time Curiosity had spent one year on Mars in August 2013, it had already transmitted over 70,000 images, and had traveled about a mile along Mars's surface.

In October 2013, Curiosity performed a detailed analysis of the argon present in the Martian atmosphere, identifying the abundance of different isotopes. From this result, scientists deduced that some meteorites on Earth do indeed have their origin on Mars. Also, the prevalence (relative to on Earth) of a heavier isotope of argon suggests that Mars did undergo massive atmospheric loss earlier in its history. Early that December, scientists, using data collected by Curiosity announced that the rover had discovered evidence of an ancient lake (which last existed about 3.7 billion years ago) in Gale crater. Remarkably, this lake would have had very low salinity, and so, unlike most other similar findings, would have been nearly freshwater. This is significant as freshwater lakes could have supported a wider variety of life.

In March 2014, Curiosity began moving toward an interesting geological site known as "the Kimberley" (shown above). This gave the rover its first opportunity to conduct geological investigations of the several sandstone varieties (rather than mudstone, which it had been previously examining) to be found at the new site. It arrived at the site at the beginning of April and began analysis, including a new drilling in May.

On June 24, 2014, Curiosity completed scheduled its primary mission of one Martian year (687 Earth days). During this time, Curiosity systematically investigated the soil composition, radiation exposure, and abundance of organic molecules. At the time of the primary mission's completion, the evidence gathered by the rover was enough to confirm that the environment of Mars had once been favorable for "supporting microbial life".

Later in June, the rover moved out of its landing area into new terrain. It ultimately arrived at the base of Aeolis Mons (also called Mount Sharp), the mountain at the center of Gale Crater, in August. Exploration of the mountain is the primary goal for MSL's first mission extension. The 5.5 km (18,000 ft) high mountain was captured in the image below, taken by the rover:

Data gathered on the lower slopes of Mount Sharp in late 2014 included a series of sediment deposits which indicated the presence of a large lake at Gale Crater early in Mars's history that lasted tens of millions of years or more. This was the first major evidence for such a long-lasting, stable body of water on the red planet.

By early 2015, Curiosity had moved out of the bottom 33 feet of altitude of Mount Sharp and had entered a region with prominent mineral veins (as shown in the image above taken on March 18, 2015, which includes a scale). Such mineral veins forms when fluids move through cracks in existing rock and leave deposits. The light and dark minerals indicate a variety of fluid compositions.

In April 2015, the rover made another exciting discovery. Data from Curiosity indicated that water vapor condenses into liquid water in the Martian soil every night and reevaporates in the morning. Even though the Martian night temperatures are well below the normal freezing point of water (they may drop to -100°F), perchlorate salts in the soil reduce the freezing point of water (just as salting roads prevents them from freezing) enough that liquid water can form. This unexpected discovery suggests that a great deal more water could exist on Mars than previously thought.

The rover spent several months investigating sand dunes as it continued its journey, learning a great deal concerning the wind patterns on the planet's surface through the inspection of sand dune "ripples" (see below). The appearance of the sand dunes was comparable in appearance to those found on Earth.

After the sand dune investigation, Curiosity crossed the Naukluft Plateau towards the upward slopes of the mountain. This journey encompassed much of the first half of 2016, during which time the rover analyzed a few additional rock samples. During its investigation of Mount Sharp, Curiosity aimed to determine what geological environments are most suitable for the preservation of organic compounds and to identify geological layers and transitions. As well as being informative in their own right, these new objectives will guide future Mars missions.

On October 1, 2016, a second extension of two years to the mission began, allowing the rover to travel further up Mount Sharp. Later that month, Curiosity made an interesting discovery: a golf-ball sized meteorite on the Martian surface.

Laser spectrometry of this darkly colored rock indicated that it was primarily composed of iron, along with some nickel and phosphorus. This type of meteorite is usually formed from the core of asteroids. Further, the study of Mars meteorites allows the comparison between its population of impacting bodies and Earth's, revealing a great deal about how the inner Solar System evolved over time.

Early in 2017, an analysis of Curiosity data brought a curious paradox into focus by not making a particular expected discovery. While investigating what is believed to be an ancient lake floor, the rover did not discover significant carbonate minerals. It was expected that in Mars's early days, an atmosphere with more carbon dioxide allowed the trapping of heat by the greenhouse effect to melt ice into liquid lakes. Were this the case, some of the CO2 would have dissolved in water, resulting in carbonates. However, no such discovery was made. This led scientists to seek alternate mechanisms for the presence of liquid water on early Mars.

In June 2017, a comprehensive study of Curiosity's findings at Gale Crater were assembled into a more complete picture of the ancient lake that existed there billions of years ago.

Of particular interest is the stratification of this lake, suggested by the differing mineral compositions of the "shallow" and "deep" walls of the crater. The stratification of lakes in this way is a phenomenon seen on Earth, and may have been conducive to different types of microbial life.

The next month, the rover began its investigation of Vera Rubin ridge, a geologic layer of Mount Sharp particularly rich in the iron oxide mineral hematite. The above image shows the location of this ridge as well as the rover's July 2017 position. Since hematite can form under wet conditions, analyzing the ridge revealed clues to Mars's ancient environments. Drilling at this site was difficult for Curiosity because an important part of the drill used to stabilize it as it pulverized rock stopped functioning back in December 2016. On the ridge, engineers experimented with a new drilling technique that did not require the stabilizers. This yielded results by early 2018, when the rover was able to obtain new samples.

Sources: Mars Science Laboratory, Wikipedia,,,,,,,,,,,,

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