The two greatest heroes of my adult life are not people, but machines: the twin Mars rovers, Spirit and Opportunity. This apparent idolatry might seem almost fundamentally misanthropic or oddly fetishist, yet rather it is born of a tendency to personify and anthropomorphise everything. David Attenborough remains firmly in place as my favourite human, alongside several mentors and acquaintances from whom I’ve had the good fortune to draw inspiration and wisdom. Yet no one, nor anything for that matter, in recent memory, has achieved the level of admiration I have developed for the two Mars rovers.
The rovers were of identical design and carried a range of instruments with which to carry out geological exploration: Panoramic cameras, a Thermal Emission Spectrometer for identifying and closely examining rock types and profiling the temperature of the Martian atmosphere, a so-calledMössbauer Spectrometer for closer investigation of rock mineralogy, an Alpha Particle X-Ray Spectrometer for analysis of the elements that make up rocks and soils, magnets for collecting dust particles, a microscopic imager for high-resolution imaging of rocks and soils, and a Rock Abrasion Tool for exposing fresh material beneath the rock and dust. Despite their six-wheeled design, the rovers were, in effect, made to mimic a human geologist, with the panoramic camera mounted on a 1.5 metre-high mast and a robotic arm which replicated the movement of a human elbow and wrist. The microscopic camera and rock abrasion tool in the rovers’ “fist” were designed to replicate the work of the geologist’s magnifying glass and hammer. With these sophisticated tools, it was hoped that the two rovers would be able to provide sufficient evidence to support the wet-Mars theory.
The two missions were launched on June 10 and July 7, 2003 and successfully landed on Mars on January 3 and January 24, 2004. The principal goal of both missions was to search for evidence of water, or a history thereof, and the rovers were sent to two different locations on opposite sides of Mars: Spirit to the Gusev Crater – a possible ancient lake-bed, roughly 14 degrees south of the Martian equator, into which the Ma’adim Vallis channel system drains, and Opportunity to the Meridiani Planum – a plain just two degrees south of the equator in the westernmost portion of Terra Meridiani, which hosts a rare occurrence of gray crystalline hematite. Hematite is usually found in hot springs or pools of water on Earth, whilst the apparent channels at Gusev closely resemble natural water courses on Earth. Hence both sites held promise of answering the question as to whether or not the surface of Mars was once partly covered with liquid water, which was strongly believed to be the case.
It is a difficult enough job landing a probe successfully on Mars – as several expensive failures have proven – let alone communicating with and driving a rover on the surface. The first successful landings on Mars were the two Viking missions of 1975, which arrived in 1976.
Both missions consisted of orbiting probes and landers, which were highly successful in providing detailed images and information about the surface of Mars, paving the way for future missions. Both landers were not mobile; they were designed to act, in effect, as stationary laboratories, testing soil samples for evidence of microbial life or organic compounds. The Viking 1 and 2 landers operated for six years and three months, and three years and seven months respectively, an extraordinary achievement in itself.
Despite this lengthy operation time, neither lander was able to discover any biosignatures that might suggest life was present or had previously existed on Mars.
Ultimately the missions only ended when the landers and orbiters failed in various ways, one by one. Whilst Viking 2’s battery failed in 1980, the tragic death of Viking 2 on November 13, 1982, was due to human error – during a software upgrade the antenna was accidentally retracted, permanently shutting off communication and terminating the mission.
It was not until 1997 that another probe successfully landed on the surface of Mars: the Pathfinder mission, which also consisted of an orbiter and lander. The major difference with the Pathfinder mission was the introduction of a mobile, roving lander -Mars Sojourner. Sojourner was just a little guy – a mere 65cm by 48cm, with a height of 30cm – it weighed in at just over ten kilograms. Operating in the Ares Vallis “flood plain”, one of the rockiest places on Mars, roughly nineteen degrees north of the equator, Sojourner’s rock analysis was able to confirm a history of volcanic activity on Mars, along with identifying erosion patterns consistent with wind and water erosion.
The mission was designed in large part as a proof of concept – that rover missions could be sent to Mars successfully for a fraction of the cost of the vastly expensive Viking missions, and to test new technologies, particularly the means by which craft were landed on other planets. Pathfinder used an innovative airbag system and effectively bounced along the surface like a giant ball.
The Pathfinder mission was considered a resounding success on all fronts – in cost-effectiveness, research significance and mission duration, which was extended two months beyond its initial target of just one month. During a mission of 83 sols (1 sol = 1 Martian day, approximately 24 hours, 39 minutes) Sojourner travelled a total of roughly 100 metres, never venturing more than 12 metres from its base-station. We thus have many lovely images of Sojourner at work on Mars photographed from its base station, a rare treat for a rover mission.
Without Pathfinder’s pioneering efforts, the successful landing of Nasa’s Spirit and Opportunity probes might not have been so easily achieved. Not to suggest for a second that it is ever easy to land a probe on another planet.
There is much more that could be said about human exploration of Mars by proxy – the Mars Voyager missions, the failed Soviet attempts to land a rover in the 1970s, the Mars Global Surveyor, the more recent Phoenix mission which landed in the northern polar region and after a successful operation, froze to death during the bitter winter, but that would be to stray too far from the base-station, as it were, and require far too many words.
Returning to the topic at hand, I’d first like to mention the dedicated teams of men and women behind Nasa’s Mars Exploration Rover Missions. From the mission designers to the people who control and monitor the activity of the rovers, to the scientists who examine the data returned by the probes, many thousands of hours of hard graft have gone into this project. Not only have the teams at Nasa worked long and gruelling hours, those controlling and monitoring the rovers have been forced to operate on Martian time – a 24 hour, 39 minute and 35 second day, sometimes for months on end. Team members were issued with special watches and expected to adjust their schedule to stay in alignment with Martian time – meaning roughly forty minutes of jet-lag every day! The watches were also fitted with accelerometers as part of a study into the effects of such a time-cycle on the human body and mind. This is no mean feat, especially when we consider that initially the mission was due to run for three months in total and yet, it is still going – eight years (!) after the rovers first landed on Mars.
It is for this reason that I have become so deeply attached to these brave little rovers, and, it must be said, to those who have kept them running through all this time. Just recently, in June 2012, Opportunity, after waking from a semi-sleep during the Martian winter, provided us with a stunning panorama of the location at which it stopped to rest back in January.
Opportunity is not only still alive, but it is doing very well in a cold world of rock, sand and fine dust. With temperatures ranging from between -5 to -87 degrees Celsius, Opportunity has survived not only freezing conditions, but also dust storms and getting bogged in a sand dune.
During the last eight years, Opportunity, which was designed to travel up to forty metres a day for a total odometry of roughly 1 kilometre, has travelled a distance of just over thirty-five kilometres. Opportunity landed, by chance, in an impact crater dubbed “Eagle” in an otherwise flat plain. On account of its airbag-aided bouncy landing, the mission controllers could hardly predict exactly where either probe would land, and the landing in Eagle was referred to humourously as a hole-in-one. It also proved to be of immense scientific interest, particularly a sedimentary outcropping dubbed El Capitan. Despite being unable to determine whether or not the layers of sediment were deposited by volcanic ash, wind or water, the discovery of the mineral Jarosite, containing an abundance of hydroxide ions, indicated it had formed in water. When Opportunity dug a trench and exposed more of the rock, it uncovered small hematite spheres, nicknamed blueberries, which are strongly believed to have formed in water. Already the mission was proving a resounding success.
Leaving the Eagle Crater, Opportunity travelled to another crater, Endurance, which it investigated between June and December 2004, methodically working its way into and around the crater.
When it moved on, Opportunity passed the some of the debris from its own heatshield, and, in an unexpectedly fortunate discovery, an intact meteorite, now known as Heat Shield Rock, was discovered nearby. This proved to be the first meteorite identified on another planet.
Shortly afterwards, as it drove towards the so-called Erebus Crater, Opportunity became perilously stuck in the sand – a problem that took six weeks to solve via Earth-based simulations, which were then successfully implemented.
Erebus Crater was a large shallow, partially buried crater, with a significant number of rocky outcrops to explore. Of course, the mission of the rovers was not merely to study the geology of the planet, but whilst at Erebus, Opportunity also photographed a transit of Mars’ moon Phobos across the face of the sun.
In September 2006, Opportunity arrived at the even more spectacular Victoria Crater. It explored the rim of the crater in detail, before returning to its original arrival point, Duck Bay. The wonderful panoramic views of the crater are some of the most evocative ever to come from the surface of another planet.
The rippled sand at the centre of the crater also makes a very alluring photographic subject.
In June of that year, Opportunity entered the crater where it remained until August 2008, conducting various analyses of the rocks and soil.
Without wishing to go into too much further detail about Opportunity’s journey across the surface of Mars, it will suffice to say that over the following years Opportunity made several stops at various other craters, including Conception, Intrepid and Santa Maria.
Ultimately, Opportunity’s destination was the much larger Endeavour Crater – no less than 23 kilometres wide – which it reached in August 2011. After spending another freezing winter sitting on the crater’s rim, Opportunity is now back in operation, doing what it does best – sophisticated geological investigation.
Of course, Opportunity has not merely been cruising about the surface taking photographs of the Martian landscape. During its travels the roverhas made many important observations and discoveries which have greatly expanded our understanding of the red planet. Principal among these were the identification of spherules – concretions which form in water, vugs – voids in rocks left by water erosion, and sulfates, which on Earth generally form when standing water evaporates. Whilst the data has been rigorously subjected to all alternative hypotheses, the nature and context of the evidence convincingly suggests the prior presence of liquid water on the surface of Mars. So much so, that this is no longer in dispute. We cannot as yet prove that there was once life on Mars, or that it may indeed continue to exist there in some form, yet we can now confidently say that Mars was once wet, and consequently, would have provided almost ideal conditions for life to emerge.
Opportunity has so far performed well beyond all expectations and provided vast amounts of data about the nature of Mars. The sheer length of the mission, and the incredible utility of having a working, mobile rover on the surface of Mars, means that more discoveries are inevitable. The Nasa website for the missions contains archives of the raw photographic images taken by both Opportunity and Spirit, along with logs of the rovers’ progress for each day of the mission, should anyone wish for more detail about the progress of the rovers. Sadly, however, whilst Opportunity continues to provide valuable data and sustain a proxy human presence on Mars, the same cannot be said of its twin, Spirit.
The Spirit rover had a rather more difficult life on Mars from the very beginning. On January 21, a mere eighteen days after its arrival, Spirit suffered a crippling problem with its flash memory that threatened to end the rover’s mission prematurely. The rover seemed to be stuck in an endless reboot loop and was not responding as it should. It was not until the 3rd of February that mission controllers identified the problem as a file-system error and remotely reformatted the entire flash memory system, allowing Spirit to resume its mission.
To make matters more difficult, the Gusev crater site where Spirit landed, turned out not to be a sedimentary lakebed after all, but rather a plain of volcanic material. Spirit was sent as fast as possible across the plains to the so-called Columbia Hills, which were believed to be geologically more ancient.
Spirit made numerous pitstops en route, perhaps most notably at the so-called Humphrey Rock, a volcanic rock which appeared to show evidence of liquid water flow in its formation.
Little of interest was found at various other craters which Spirit passed, and eventually, after 129 Sols, Spirit finally clambered up the slopes of the Columbia Hills. Over the following two years, Spirit explored these hills– places with names such as Husband Hill, Cumberland Ridge, Larry’s Lookout, Tennessee Valley, Home Plate, McCool Hill, Low Ridge Haven and so on.
In 2006, Spirit finally came down from the hills to explore an area known as Home Plate, where it was to remain for the rest of its working life. Home Plate turned out to be a large “explosive” volanic deposit, surrounded by basalt which is believed to have exploded upon contact with water. The presence of salty water seemed confirmed by the high concentration of chloride ions in the surrounding rocks.
Throughout this time, Spirit encountered more difficult conditions and mechanical problems than Opportunity. One of Spirit’s front wheels had long been playing up, and on March 16, 2006, the wheel stopped working altogether. Spirit attempted to crawl backwards, dragging its wheel, to the north face of McCool Hill, where it was to spend the Martian winter, yet was unable to manage the ascent and was instead sent to winter in Low Ridge Haven.
The broken wheel on Spirit laterturned out to be a blessing of sorts, when its dragging through the soil uncovered a subsurface layer of silica rich dust in December 2007.
The resulting analysis suggested the silica was likely produced in a hot-spring environment, again suggestive of a water-rich history.
The site near the Gusev Crater was especially dusty and throughout its mission, Spirit’s solar arrays faced increasingly reduced capacity on account of the dust coating.
In 2007 dust storms threatened to shut Spirit down altogether, reducing the production capacity of its solar panels from 700 watt-hours per day to a mere 128, below the minimum threshold for sustaining battery charge to power the rover’s heaters.
To avoid risk of the rover shutting down completely, Spirit was kept in temporary hibernation on its lowest possible power setting. For two weeks between November 29 and December 13, 2008, on account of the so-called Solar Conjunction – when the sun is between Earth and Mars –no communication was possible with either rover.
Even when Spirit revived from its troubled hibernation, its solar arrays still struggled to produce sufficient power. It was not until February 2009, when a fortunate wind cleaned some of the dust off Spirit’s panels, increasing its energy production to roughly 240 watts per day, that the rover seemed ready to reach full exploration capacity once again. Unfortunately, however, on the first of May 2009, Spirit became stuck in soft soil and proved unable to free itself. With the failure of another wheel, the engineers and controllers were unable to extract Spirit from its location after numerous attempts to do so, via various simulations and manoeuvres. Eventually the rover’s purpose had to be redefined as a stationary research platform, but in truth, Spirit’s run had come to an end. The last communication was on March 22, 2010, the 2210th day of the mission. The cold, it appears, was the ultimate culprit. In previous winters, Spirit had been able to park itself on a sun-facing slope, allowing it to winter in temperatures averaging -40. Stuck out on the plains, however, Spirit endured temperatures of closer to -55 Celsius – more than its reduced energy production could cope with.
Many attempts were made to regain contact with Spirit, and it was not until May 2011 that the mission was officially declared over. The final entry for Spirit’s log on the Nasa website reads as follows:
SPIRIT UPDATE: Spirit Remains Silent at Troy - sols 2621-2627, May 18-24, 2011:
More than 1,300 commands were radiated to Spirit as part of the recovery effort in an attempt to elicit a response from the rover. No communication has been received from Spirit since Sol 2210 (March 22, 2010). The project concluded the Spirit recovery efforts on May 25, 2011. The remaining, pre-sequenced ultra-high frequency (UHF) relay passes scheduled for Spirit on board the Odyssey orbiter will complete on June 8, 2011. Total odometry is unchanged at 7,730.50 meters (4.80 miles).
Despite its incredible successes and the unimaginable extension of its mission, the loss of Spirit was a great disappointment for the mission controllers. Once it had become clear how well the rovers were performing on Mars, Nasa had made the decision to drive them until they broke down, and this was certainly the fate of Spirit. When the mission was finally abandoned, Mars Exploration Rover Project Manager John Callas, sent a letter to his team, both celebrating and farewelling the great success of the tough little rover. An abridged version follows:
Last night, just after midnight, the last recovery command was sent to Spirit. It would be an understatement to say that this was a significant moment. Since the last communication from Spirit on March 22, 2010 (Sol 2210), as she entered her fourth Martian winter, nothing has been heard from her. There is a continued silence from the Gusev site on Mars.
Importantly, it is not how long the rover lasted, but how much exploration and discovery Spirit has done.
Each winter was hard for Spirit. But with ever-accumulating dust and the failed wheel that limited the maximum achievable slope, Spirit had no options for surviving the looming fourth winter. So we made a hard push toward some high-value science to the south. But the first path there, up onto Home Plate, was not passable. So we went for Plan B, around to the northeast of Home Plate. That too was not passable and the clock was ticking. We were left with our last choice, the longest and most risky, to head around Home Plate to the west.
It was along this path that Spirit, with her degraded 5-wheel driving, broke through an unseen hazard and became embedded in unconsolidated fine material that trapped the rover. Even this unfortunate event turned into another exciting scientific discovery. We conducted a very ambitious extrication effort, but the extrication on Mars ran out of time with the fourth winter and was further complicated by another wheel failure.
With no favorable tilt and more dust on the arrays, Spirit likely ran out of energy and succumbed to the cold temperatures during the fourth winter. There was a plausible expectation that the rover might survive the cold and wake up in the spring, but a lack of response from the rover after more than 1,200 recovery commands were sent to rouse her indicates that Spirit will sleep forever.
But let’s remember the adventure we have had. Spirit has climbed mountains, survived rover-killing dust storms, rode out three cold, dark winters and made some of the most spectacular discoveries on Mars. She has told us that Mars was once like Earth. There was water and hot springs, the conditions that could have supported life. She has given us a foundation to further explore the Red Planet and to understand ourselves and our place in the universe.
But in addition to all the scientific discoveries Spirit has given us in her long, productive rover life, she has also given us a great intangible. Mars is no longer a strange, distant and unknown place. Mars is now our neighborhood. And we all go to work on Mars every day. Thank you, Spirit. Well done, little rover.
And to all of you, well done, too.
Indeed, to all of those people who made this possible, well done. I rank this among the greatest of human achievements. Not merely landing a robotic vehicle on an inhospitable planet thousands of kilometers from the Earth, but successfully exploring the surface of said planet for eights years ongoing, is truly incredible.
People may well wonder what the point of all this is and whether or not we can justify the cost of extra-planetary exploration. I would argue that the question of whether or not life exists on other planets, whether or not its genesis has occurred independently on other worlds and is, perhaps, endemic to the universe, is worth answering. If not merely for the reassurance that the universe might be teeming with life, then also as a means of addressing long-standing religious and philosophical understandings of the origins of life and its uniqueness. This a fundamental question that lies at the heart of human enquiry, and yet such exploration is by no means merely for philosophical purposes. There are also many practical reasons for exploring other planets, particularly one which has had a water-rich past, and yet appears now to be as dry as a bone. Where did Mars’ water go, and was it the result of catastrophic climate change, or the result of the solar wind’s stripping away the atmosphere once Mars’ magnetic field had weakened?
The cost of these missions is negligible when cast against the vast spending on military budgets the world over, and, it must be said, when compared to the cost of putting people in space. There have long been advocates of abandoning attempts to maintain the international space station, or put people back into orbit or on the moon. Do we really need to go ourselves when we can send probes there for a fraction of the cost and risk? Even were it only for the sake of satisfying our insatiable curiosity to know what is out there, the exploration of our solar system and the attempts to answer fundamental questions about our own origins and future via planetary geological survey are worth conducting. Ultimately, it will become a target of economic exploration – indeed, recently, several start-ups have begun to raise capital for near-earth asteroid mining. If we can pull the resources we need from space efficiently, where they exist in an unimaginable abundance, then it would greatly relax pressures on our own planet to dig up and destroy valuable ecosystems.
If you have not already done so, I strongly recommend logging into Google Earth and, using the drop down menu at the top, switching from Earth to Mars. Google Mars is a fantastic tool for exploring the surface of the red planet and learning more about its geology and geography. Mars might be just over half the size of Earth, yet it holds the largest mountain in the known solar system – Olympos Mons, which rises to a height of just under 22,000 metres – Everest clocks 8853. It also has one of the largest known canyon systems – Valles Marineris – which is 4,000 km long, 200 km wide and up to 7 km deep. The Grand Canyon, by comparison, would be a mere tributary. Simply searching for Spirit or Opportunity will take you to their landing sites, from which their journeys might be followed. The panoramic photographs are well worth delving into.
There are further missions planned to Mars, though recent budget constraints have also seen various mission abandoned. This year, on August 5, in what may prove to be the last touchdown for a while, Nasa will attempt to land its latest rover dubbed Curiosity or the Mars Science Laboratory. This will be the largest rover ever sent to Mars – weighing in one tonne and roughly the size of an SUV – and it is hoped that it too might perform far beyond its initial mission plan.
I will be keeping my fingers crossed that all goes well and hoping for an early birthday present of some magnificent new images from the surface of the planet.
So, enough said! Long live Spirit and Opportunity! - Two of the most incredible machines ever built and a testament to the brilliance of humans when they work tirelessly in pursuit of answers to the eternal questions of life, the universe and everything. Hear hear!
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