Concepts for Mars sample return missions, like this, have been around for decades, but there is now new and growing momentum to return samples from the Red Planet. (credit: NASA/JPL-Caltech)
In November 2018, NASA Associate Administrator for Science Thomas Zurbuchen announced the selection of Jezero Crater as the landing site of the Mars 2020 rover. Mars 2020—which will most likely be renamed next year to something a bit catchier—will launch in July 2020 and land on Mars on February 18, 2021. It will then rove around Jezero, using a highly sophisticated sampling system to gather pieces of Mars and seal them in tubes each about the size of a pencil. But this isn’t just another Mars mission. Mars 2020 represents the most concrete step in achieving a goal that has been a top priority for American planetary scientists for nearly 50 years: returning samples from Mars. Launching and landing Mars 2020 will not only be an important engineering achievement, but a major psychological one. After decades of false starts and even reversals, the goal of Mars sample return—or MSR as it has long been known in planetary circles—now has real momentum.
Mars already has hosted a small flotilla of orbiters, landers, and rovers. Another lander, three rovers, and two orbiters are scheduled to arrive in two years. Yet returning samples from the surface long has been the ultimate goal for Martian studies. The instruments humanity has sent to that world have been marvels of sophistication and miniaturization. However, they cannot begin to match the sophistication and breadth of instruments used by scientists on Earth.
As an example of the limitations of instruments we can send to Mars, consider a recent scientific paper that announced that organic molecules had been found in material analyzed by one of the Curiosity rover’s chemistry instruments. The fragments of carbon-containing molecules detected suggested that they may have come from much more complex organic molecules known as kerogens. These complex organic molecules, if they were indeed the source of the fragments, can come from meteorites, interplanetary dust, Martian geology, or biology. There’s simply not the room, mass, or power available on a lander or rover to definitively answer the question of what the parent molecules were or how they were formed. We are left with tantalizing and ultimately frustrating clues. If Curiosity’s samples were in Earth laboratories, scientists could both pursue the identity of these parent molecules and how they were created.
Similarly, an international science team recently claimed to have found the oldest known terrestrial fossils on Earth in western Australia, estimated to be 3.4 billion years old. Their methods illustrate the need to return samples to explore the question of life—ancient or contemporary—on Mars. The likely microfossils are just 10 micrometers across, found in the spaces between the sand grains of an ancient beach turned to sedimentary rock. Using a highly sensitive X-ray absorption spectroscopy enabled by the energy produced by a synchrotron, a combination that cannot be packaged aboard a rover, scientists found residual chemicals expected from fossilized biological remains. Tiny deposits of pyrite, fool’s gold, found on the microfossils could be the product of sulfur-based metabolisms that these creatures could have employed to extract energy in a world without an oxygenated atmosphere. Analyses at these tiny scales are beyond what instruments on a spacecraft can do. But they could be performed in terrestrial laboratories on samples returned from Mars.
NASA and the European Space Agency (ESA) have laid out an ambitious plan involving three launches and multiple craft as well as a terrestrial sample facility. (credit: Caltech/JPL)
The early origins of Mars Sample Return
Recognizing these needs, the first proposals for robotically returning a sample from Mars date from the early 1970s. As NASA was working on the Viking Mars missions, Martin Marietta conducted a study of robotic rendezvous and docking in Mars orbit, which was then considered one of the most difficult aspects of robotic sample return. Other major challenges included designing a Mars ascent vehicle that could survive the coldness of Mars and lift off the surface successfully to reach orbit. The two Viking missions in 1976 proved that NASA could land a spacecraft on Mars. Viking could have formed the basis of a sample return mission if one had been approved.
But by the mid-1970s, the American planetary science community viewed Mars sample return as a long-term goal, not a near-term one. Scientists didn’t know enough about the surface of Mars to identify the most compelling site to sample. The science community advocated for a precursor mission, or missions, to better characterize the Martian surface. Scientists speculated as to when they would know enough to confidently pursue a sample return mission. This debate continued throughout the 1970s and 1980s.
But the Viking experience had created a problem: although Viking had many science goals, the one that gained the most attention was detecting life on Mars; when Viking failed to do that, political and public support for further Mars missions evaporated. The American planetary science community continued to endorse Mars sample return, but they could not find support for any Mars missions throughout the 1980s, let alone an incredibly expensive one.
By the 1990s NASA finally restarted Mars exploration after a long hiatus. Unfortunately, the Mars Observer spacecraft failed to reach Mars orbit in 1993, again delaying Mars exploration. Then, in 1996, a science team claimed to have discovered evidence of fossilized life in a meteorite from Mars found in the Antarctic. While the claim was not been widely embraced by the science community, it did spark new White House interest in the red planet.
By the latter 1990s, Mars sample return gained increasing support within the scientific community and companies began conducting engineering studies. It looked as though NASA would start working on an actual Mars sample return mission by the early 2000s. But in 1999 NASA lost both the Mars Climate Orbiter and the Mars Polar Lander spacecraft, leading the agency to re-evaluate its Mars strategy. As part of NASA’s new strategy for exploring Mars, the agency called a halt to the sample return effort, concluding the science community still did not yet know enough about Mars to know where to obtain the best sample. It was pointless to spend billions of dollars to bring back a rock no different than several Martian meteorites that had already fallen to Earth. What they needed was a series of missions that would enable the selection of a high-quality sample.
The Mars Exploration Program
NASA, under its new Mars Exploration Program, was soon launching those kinds of missions: the rovers Spirit and Opportunity that landed in 2004, and the Mars Reconnaissance Orbiter, which reached Mars in 2006. Europe’s Mars Express orbiter began its studies in 2004. The Mars Science Laboratory, later named Curiosity, was originally scheduled for a 2009 launch that was delayed to 2011, at significant expense. Whereas Sprit and Opportunity were designed to follow the water, Curiosity was designed to follow the carbon, and Mars Reconnaissance Orbiter was intended to create a global database of how the water and other conditions required for the creation and sustainment of life fit together, collectively exploring the past or present “habitability” of Mars. One could argue that the missions that have been orbiting and roving on Mars for the past two decades are essentially part of the Mars sample return effort, or at least the first, necessary stage of a sample return strategy.
What these missions revealed about Mars led to a dramatic change in the goals for the sample return. The earliest concepts had the lander collect samples from the immediate vicinity of the lander, based on the belief that any material returned from Mars would be valuable. This strategy would have been similar to China’s plans to return samples from the Moon. The planned Chinese Chang’e-5 mission aims to understand how the youngest lunar mare formed, and a sample gathered directly at the landing site anywhere within a broad region will provide the material to answer this question. Similarly, a hoped-for American return mission to explore the Moon’s mantle and cratering history depends on impacts to disperse rock fragments of key geological units across the surface so that it can rake up a sample collection from next to the lander. A planned Chinese Mars sample return mission to launch in 2028 apparently also will take samples from the immediate landing site.
However, western scientists turned away from this approach for Mars. Partially, this was due to the discovery that more than 100 known samples of Mars were already on the Earth, expelled from the Martian surface by impacts and delivered to our world as meteorites. Second, scientists came to realize that the samples that best record the earliest history of Mars—from an epoch lost on the much more geologically active Earth—are found distributed across local regions. These are also fragile materials, such as sediments, that would not survive impacts to be delivered naturally to the Earth. Plans for a Martian sample return came to include a dedicated rover mission that would collect and cache a diversity of samples from across an ancient and geologically diverse site.
The Martian gambit
This brings us to the current decade. In 2011, the National Research Council produced Vision and Voyages for Planetary Science in the Decade 2013–2022, otherwise known as the planetary science decadal survey. The decadal survey recommended a Mars sample caching mission as the highest priority for a large-class mission (a mission costing over $1 billion at the time.). The Mars community did not recommend any other missions, putting all their chips on the table. This was a potentially controversial move because sample return would not address all the areas of pressing scientific inquiry at Mars, leaving some researchers in the Mars community without a mission to advance knowledge in their respective fields. There also was a possibility that NASA—and the decision makers who controlled the agency’s budget—might not fund the first steps for sample return because of concerns about the cost. But the decadal committee concluded that after more than four decades of waiting for samples from the Red Planet, placing any other mission on the list of priorities—allowing policymakers the option of choosing a lower-cost mission and kicking the can of sample return down the road yet again—was no longer practical. The Mars community had systematically worked through its list of scientific questions and the most important issues remaining required carefully selected samples from Mars to be brought back to Earth. Sample return is the mission that the Mars community believes has the greatest potential for advancing Mars science.
One of the benefits of Mars sample return is that samples can be shared around the world, taking advantage of non-American scientific capabilities. This also makes sample return attractive for international participation, something that many view as necessary for political support for such an expensive mission. At the time, NASA was in discussions with the European Space Agency (ESA) to participate in its ExoMars program. NASA and ESA would each build rovers for Mars, and NASA’s rover would focus on collecting samples for eventual return to Earth. ESA would build an orbiter on which NASA would provide instruments, and NASA would launch all the spacecraft. The program was an ambitious and costly undertaking. The 2011 decadal survey prioritized NASA’s involvement in ExoMars, but recommended that investment in the Mars Astrobiology Explorer-Cacher (MAX-C) rover be reduced from $3.5 billion to $2.5 billion. Mission planners at NASA worked to find efficiencies and descopes to the rover, while NASA management negotiated with ESA to encourage the Europeans to take on a greater share of the cost. After an extended effort in which the agencies were able to realize the recommended cost levels for NASA, the US Office of Management and Budget (OMB), concerned about cost overruns on Curiosity and the James Webb Space Telescope, and unwilling to commit the government to later missions required to retrieve the samples, ordered NASA to back out of the program, damaging NASA’s relationship with ESA.
NASA managers did not want to risk losing the workforce and capabilities developed over decades conducting Mars exploration—particularly regarding entry, descent, and landing—and quickly began looking for another Mars mission. John Grunsfeld, then associate administrator for science, initially proposed a medium-class ($700 million) orbiter or rover for Mars but immediately encountered resistance from the science community over the fact that neither mission followed the recommendation of the decadal survey. He established a working group at NASA to determine a path forward for NASA’s Mars program. The group found that NASA could follow any of several paths at Mars to meet its objectives, but all of them required a mission leading to eventual sample return. In essence, the group said, “follow the recommendations of the decadal survey.”
There have been reports that the success of the Curiosity landing in summer 2012 prompted President Barack Obama to ask what other exciting missions NASA was planning for Mars. This high-level political interest, combined with the working group’s report, prompted approval of the Mars 2020 mission late that same year. Mars 2020 would be based upon the successful Curiosity entry descent and landing system and the successful rover design.
Informed sources have told us that for several years, up to around 2016, officials at OMB fought the inclusion of the sample caching system on Mars 2020. OMB likely could not do this unless there was at the very least indifference to the sample return mission within the Obama Administration. OMB takes its cues from the senior elected leadership, and without active and continued support for major initiatives, OMB budget examiners revert to their baseline skepticism of expensive programs and long-term project commitments. If the Mars 2020 project had gone over budget at that time, OMB might have gutted it by forcing removal of the sample caching equipment, effectively neutering the spacecraft. Mars 2020 stayed on budget during this time.
What OMB reportedly was able to do at this time was prevent the expenditure of nearly any money on developing technology required to return samples from Mars—another key recommendation of the 2011 decadal survey. Mars sample return technology development funding could have started in 2013, but for four years it was nearly non-existent. We are told that NASA officials were forbidden from even publicly mentioning Mars sample return or engaging in talks with potential foreign partners about such a mission. OMB’s opposition was apparently based upon their general opposition to all expensive space missions, and their skepticism that NASA could control the costs of such a mission.
On the way to bringing back pieces of Mars
The situation was different after the change in administrations starting in 2017. New people in the executive branch apparently applied pressure to OMB officials to stop their opposition to further Mars missions, and in the summer of 2017 NASA was finally able to indicate that it had begun working on a “focused and rapid” Mars sample return design architecture. The Jet Propulsion Laboratory, with approval from NASA, began developing technology required for capturing a sample canister about the size of a soccer ball into orbit around Mars. By fall 2017, two companies also began testing technology for rocket motors to lift a sample canister off Mars.
By April 2018, NASA announced the signing of “a joint statement of intent” with the European Space Agency to develop a Mars sample return plan. ESA has issued contracts to study the fetch rover that would retrieve the samples on Mars and a robotic arm that would load them into the return capsule. ESA is also studying the return vehicle that would capture the capsule in orbit. With ESA building the fetch rover and the arm and possibly the return spacecraft, NASA will not have to build these expensive components of the mission. But the agency will certainly have its hands full developing the complex and expensive Mars ascent vehicle.
To return the Mars 2020’s samples, both NASA and ESA must formally approve their portions of missions to follow the 2020 rover. ESA’s approval would come through its ministerial meeting to be held this coming November. In the meantime, that agency’s managers have released a call for proposals for sample return orbiter. This would allow ESA to quickly start on development if its ministers approve participation in the sample return program.
NASA and ESA’s plans call for careful choreograph of launches and operations to return samples to Earth as early as 2031. (credit: Caltech/JPL)
On the American side of the Atlantic, Congress has provided NASA with $50 million this year for preparatory work. The administration has proposed $109 million for the next fiscal year to work on future Mars missions with most of that to go to preparing for a sample return. (The House of Representatives’ bill supports this funding and supports a 2026 launch date. The Senate has yet to act.) Within NASA, the Mars program has received permission to formally develop the budget for its potential contributions to allow a NASA decision on the program next year.
After decades of considering and planning a Mars sample return, it appears that the critical momentum finally may be in place for the program. The first mission in the series, the 2020 rover, is on track to launch next summer. All the right preparatory steps are being taken on both sides of the Atlantic. The crucial decisions will come this fall for ESA and likely for NASA with the release of the President’s fiscal year 2021 budget, which could provide a formal new start authority and budget—or not.
If America has a new president the following year, his or her administration would need to confirm its support. Still, this seems to be a good time to be hopeful. By then the Mars 2020 rover will be traversing Jezero Crater collecting carefully curated samples of Mars. That may truly change the psychology concerning Mars sample return. With actual samples resting on Mars, there will be increasing calls—and possibly political support—to bring them back to Earth for analysis. Those samples may not definitively answer whether life once existed on Mars, but they will get humanity much closer to answering that question than we have ever been in all the millennia since humans have stared at the Red Planet and wondered if there was anything alive on it.
For more information on the developing NASA and ESA Mars sample return program, we recommend this presentation from June 2019.
- National Research Council. Opportunities and Choices in Space Science, 1974. Washington, D.C.: The National Academies Press, 1975.
- NASA Press Release, “NASA Outlines Mars Exploration Program for Next Two Decades.” October 26, 2000.
- Mars Program Planning Group, “Summary of the Final Report.” September 25, 2012.
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