With the abundance of discoveries in planetary science this year, none was truly more important to the future of human exploration of other planets than the long-awaited confirmation that liquid water flows on the surface of present-day Mars. The discovery by NASA’s Mars Reconnaissance Orbiter came during a year of increased public attention toward Martian exploration as orbiters and rovers of the red planet returned finding after finding.
The Waters of Mars: MRO’s landmark discovery
It was a search hundreds of years old.
On 28 September 2015, NASA announced what so many had sought for so long – a landmark discovery by the Mars Reconnaissance Orbiter (MRO) of definitive evidence of recent salt water flows on Mars.
The discovery confirmed long-held suspicions and mounting evidence from MRO and placed Mars into a category of planet that until then only had one occupant: planets with current water flow activity.
“Our quest on Mars has been to ‘follow the water’ in our search for life in the universe, and now we have convincing science that validates what we’ve long suspected,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate.
“This is a significant development, as it appears to confirm that water is flowing today on the surface of Mars.”
The confirmation came from an area of downhill flows, known as Recurring Slope Lineae (RSL), that have often been described as being possibly related to liquid water.
“The detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks,” said Lujendra Ojha, lead author of a report on these findings published 28 September by Nature Geoscience.
While the historic nature of the discovery cannot be understated, the confirmation of present-day liquid water on the surface of Mars continues to lend evidence to the hypothesis that Mars was once a habitable planet that could have harbored life.
Moreover, the discovery holds potentially significant implications for current-day life on Mars. For on Earth, where there’s liquid water, there’s life.
However, the more immediate consideration is how this discovery will influence future human missions to the red planet.
The presence of not only water ice at the Martian poles but flowing, briny water on other areas of the planet under certain conditions holds great significance for future human exploration and the use of in-situ resources that may be vital to any human exploration of Mars.
Nonetheless, the groundbreaking discovery of liquid water on Mars was not the only accomplishment of MRO in 2015.
In January, the MRO team revealed that cameras onboard the orbiter had located the Beagle 2 Mars Lander, built by the United Kingdom as part of an ESA mission to the red planet, that disappeared during landing operations on 25 December 2003.
A series of three observations with MRO’s High Resolution Imaging Science Experiment camera showed Beagle 2 partially deployed on the surface of Mars, ending the mystery of what happened to the mission.
The MRO images revealed that Beagle 2 survived its landing and at least partially deployed its solar arrays; however, the solar arrays under which the primary communications antenna was located failed to deploy, thus eliminating the chance of Beagle 2 establishing contact with Earth and having enough power to perform its mission.
In February, MRO completed is 40,000th orbit of Mars before passing smoothly through a communications blackout with its controllers as Mars and Earth entered conjunction – they were directly opposite the Sun from one another – in June.
In July, NASA announced that MRO’s orbit would be altered to place the spacecraft into a better orbit to serve as a communications relay for the 2016 arrival and landing of InSight – a mission that in December 2015 was delayed for at least two years due to an instrumentation problem that precluded the ability to make the March 2016 launch window.
This orbital change, combined with the additional maneuver to return MRO to its original orbit once InSight lands on Mars, are projected to leave MRO with more than 187 kilograms (413 lbs) of propellant – enough to ensure 19 years of additional operations of MRO as long as its systems and computers survive that long.
For arguably the most famous of NASA’s rovers, Curiosity began 2015 investigating the effects of water on the slopes of Mount Sharp.
Specifically, Curiosity drilled into rocks at Mount Sharp and discovered significant quantities of jarosite, an oxidized mineral containing iron and sulfur that forms in acidic environments.
The find hints at the long-ago effects of water far more acidic than any evidenced water effects thus far seen on Mars and raised questions of whether the more acidic water was part of the overall environmental conditions when sediments began building on the side of Mount Sharp or if it was deposited at the site afterward.
Moreover, by the end of March, Curiosity had analyzed rock samples drilled over the last several months at two-tone mineral veins (dark on both edges and white in the middle), resulting in more evidence and clues about multiple episodes of fluid movements across the surface of Mount Sharp.
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The mineral veins hold the geologic record of the area’s different stages of evolution because the mineral veins form when fluids moved through cracks in the rocks and deposit minerals in the fractures.
For these veins, the dark material that lines the fracture walls reflects an earlier episode of fluid flow than the white, calcium-sulfate-rich veins.
Overall, investigation of these veins fell directly into Curiosity’s primary scientific mission to examine environments that offered favorable conditions for microbial life on ancient Mars and the changes from those environments to drier conditions that have prevailed on Mars for more than three billion years.
Following this examination, Curiosity made a brief detour to conduct a closer look at a hillside site where the ancient valley was carved out and subsequently refilled.
The rover then continued its drive up Mount Sharp toward its next primary investigation site.
However, that target site proved too treacherous to reach because of slippery slopes the rover would have had to navigate.
Instead, in late-May Curiosity’s teams drove the rover to an alternate site where two distinctive types of bedrock meet, allowing scientists to investigate an outcrop that contains contact between the pale rock unit the mission analyzed lower on Mount Sharp and a darker, bedded rock unit that the mission had not yet examined up close.
Such contact zones can hold clues about ancient changes in environment, from conditions that produced the older rock type to conditions that produced the younger one.
Upon further investigation of the area, Curiosity also found sandstone with grains of different shapes and colors – indicating that some of the sandstone grains were local while others had travelled great distances to reach this location.
Curiosity subsequently spent most of May and June exploring the bedrock contact zone after moving slightly downhill, where it discovered high levels of silica, a rock forming compound containing silicon and oxygen commonly found on Earth as quartz, in the bedrock.
By August, investigations at the bedrock contact layer were complete, and Curiosity continued its southwest drive further up Mount Sharp.
At this time, approximately three years after its landing on Mars, Curiosity’s total odometry stood at 11.1 km (6.9 miles).
By the end of August, Curiosity’s onboard cameras identified an area of dark sandstone containing indications that the sandstone formed first as sand dunes that were subsequently cemented into rock.
This sandstone turned out to be just the kind of sandstone Curiosity’s teams were hoping to find and was also located near sandstone that appeared to have been altered by fluids – likely groundwater.
By mid-November, after investigating this sandstone, Curiosity was once again on the move toward higher layers of Mount Sharp when mission scientists decided to take advantage of a chance to study modern Martian activity at mobile sand dunes near the rover’s location.
The dunes, called Bagnold Dunes, skirt the northwestern flank of Mount Sharp and represented an opportunity for Curiosity to do what no rover had previously done: visit a sand dune.
Previous missions, such as Spirit and Opportunity, had observed sand ripples and drifts but not dunes.
“We’ve planned investigations that will not only tell us about modern dune activity on Mars but will also help us interpret the composition of sandstone layers made from dunes that turned into rock long ago,” said Bethany Ehlmann of the California Institute of Technology and NASA’s JPL.
By 10 December, Curiosity had begun up-close investigations of the sand dunes measuring two stories in height.
At the time, mission operators planned to use Curiosity’s arm to collect a sample of the dune material for analysis within the roving laboratory’s instruments.
NASA’s intrepid little rover began 2015 having traveled 41.62 kilometers (25.86 miles) while proceeding south along the rim of Endeavour Crater to a location known as Marathon Valley, where water-related minerals have been detected from orbit.
At the start of the year, Opportunity was operating in “no-flash mode,” meaning its flash memory was inoperable and the rover was incapable of storing images and data in its flash memory during overnight sleep hours, as its teams worked on a fix to the issue.
On 25 January (UTC), Opportunity and its teams marked the 11th anniversary of the rover’s landing on Mars for a mission that was only supposed to last 90 days.
Throughout February, Opportunity progressed across the Martian surface before its control teams stopped the rover at the edge of a plateau to investigate a series of highly unusual blocky, dark-grey rocks.
Opportunity’s investigations revealed the composition of at least one of the rocks to be high in concentrations of aluminum and silicon, a composition never-before observed on Mars.
Opportunity spent nearly an entire month observing these unusual rocks before its team stopped all activity on the rover to reformat Opportunity’s memory banks.
The reformatting followed several flash memory issues and nearly three months of “no flash memory” operations aboard the rover and was completed on 20 March.
The reformatting restored flash memory ability and overnight data storage on six of seven flash memory banks – the seventh of which was found to be the home of the error causing the flash memory issues aboard the rover.
With flash memory restored, Opportunity resumed driving on 23 March and surpassed a driving distance of over one marathon (42.195 km – 26.219 miles) over the course of an 11 year journey on 24 March 2015.
However, just three days later, Opportunity experienced yet another amnesia event related to its flash memory.
While this amnesia event did not result in the loss of any scientific data, the event nonetheless indicated that Opportunity’s teams had not yet identified the root cause of all of the amnesia events that plagued the rover prior to 2015.
Nonetheless, Opportunity soldiered on and passed without issue through the June solar conjunction between Earth and Mars and resumed normal operations once communication was reestablished.
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Following the solar conjunction, Opportunity’s teams began preparing the rover for is unprecedented seventh Martian winter.
Throughout July, Opportunity’s team drove the rover toward a north-facing slope in Marathon Valley to allow Opportunity to angle its solar panels toward the Sun during Mars’ southern hemisphere’s winter months – which began in August.
Moreover, the winter location allows Opportunity to continue exploring this area of Marathon Valley throughout winter, specifically allowing the rover to perform a walkabout of the valley to identify potential future investigation targets near the valley’s floor.
For Opportunity, the shortest daylight period for the seventh Martian winter will occur in January 2016.
As of 8 December, Opportunity’s solar arrays were producing 407 watt-hours of energy with an improved solar array dust factor of 0.66 – enough to allow teams to proceed with a planned rock grinding event to hopefully unlock clues as to the origin of clay spectral signatures detected in Marathon Valley.
NASA’s MAVEN orbiter, which arrived at the red planet in September 2014, began its primary science mission in 2015, had its mission officially extended by NASA, and accomplished one of its major objectives.
In the first half of 2015, NASA officially extended MAVEN’s mission from November 2015 to September 2016, thus allowing the spacecraft to remain active in orbit of Mars for nearly a full Martian year.
By the end of 2015, MAVEN had accomplished one of its primary mission objectives: determining the rate at which the Martian atmosphere is currently losing gas to space via stripping by the solar wind.
MAVEN measurements indicate that the solar wind strips away gas at a rate of about 100 grams (roughly 1/4 pound) every second.
In addition, a series of dramatic solar storms hit Mars in March 2015, and MAVEN found that atmospheric loss was accelerated during those events.
The combination of greater loss rates and increased solar storms in the past suggests that loss of atmosphere to space was likely a major process in changing the Martian climate.
“We’ve seen that the atmospheric erosion increases significantly during solar storms, so we think the loss rate was much higher billions of years ago when the sun was young and more active,” said Bruce Jakosky, MAVEN principal investigator.
However, it wasn’t just NASA that saw success at Mars in 2015.
India’s MOM spacecraft received the first of its mission extensions following the completion of its primary six-month orbital investigation.
The spacecraft and India also celebrated MOM’s one year arrival anniversary, which coincided with the Indian Space Research Organisation’s (ISRO’s) release of the “Mars Atlas” detailing the photographs and scientific discoveries MOM has made thus far.
Currently, MOM remains in Martian orbit continuing a multitude of observations of the red planet while its controllers monitor the spacecraft and plan for a variety of technical aspects regarding command of MOM as it continues to consume propellant, as that will be a driving force in the duration and longevity of the mission which has already surpassed initial expectations.
(Part four of NASASpaceflight.com’s four-part 2015 Year In Review will be published in the coming days.)
(Click here for Part 1 of NASASpaceflight.com’s 2015 Year In Review.)
(Click here for Part 2 of NASASpaceflight.com’s 2015 Year In Review.)