Planetary Protection is a “Wicked” Problem

The Viking landers were baked for 30 hours after assembly, a dry heat sterilization that is considered the gold standard for planetary protection.  Before the baking, the landers were given a preliminary cleaning to reduce the number of potential microbial spores.  The levels achieved with that preliminary cleaning are similar to what is now required for a mission to Mars unless the destination is an area known to be suitable for Martian life.  In that case, a sterilizing equivalent to the Viking baking is required.  (NASA)

The only time that a formally designated NASA “life detection” mission was flown to another planet or moon was when the two Viking landers headed to Mars forty years ago.

The odds of finding some kind of Martian life seemed so promising at the time that there was little dispute about how much energy, money and care should be allocated to making sure the capsule would not be carrying any Earth life to the planet.  And so after the two landers had been assembled, they were baked at more than 250 °F for three days to sterilize any parts that would come into contact with Mars.

Although the two landers successfully touched down on the Martian surface and did some impressive science, the life detection portion of the mission was something of a fiasco — with conflict, controversy and ultimately quite a bit of confusion.

Clearly, scientists did not yet know enough about how to search for life beyond Earth and the confounding results pretty much eliminated life-detection from NASA’s missions for decades.

But scientific and technological advances of the last ten years have put life detection squarely back on the agenda — in terms of future searches for fossil biosignatures on Mars and for potential life surviving in the oceans of Europa and Enceladus.  What’s more, both NASA and private space companies talk seriously of sending humans to Mars in the not-too-distant future.

With so many missions being planned, developed and proposed for solar system planets and moons, the issue of planetary protection has also gained a higher profile.  It seems to have become more contentious and to some seems far less straight-forward as it used to be.

A broad consensus appears to remain that bringing Earth life to another planet or moon, especially if it is potentially habitable, is a real possibility that is both scientifically and ethically fraught. But there are rumblings about just how much time, money and attention needs to be brought to satisfying the requirements of “planetary protection.”

In fact, it has become a sufficiently significant question that the first plenary session of the recent Astrobiology Science Conference in Mesa, Arizona was dedicated to it.  The issue, which was taken up in later technical sessions as well, was how to assess and weigh the risks of bringing Earth life to other bodies versus the benefits of potentially sending out more missions, more often and more cheaply.

It is not a simple problem, explained Andrew Maynard, director of the Risk Innovation Lab at Arizona State University.  Indeed, he told the audience of scientists that it was a “wicked problem,” a broadly used terms for issues that are especially complex and involve numerous issues and players.


A primary barrier to keeping microbes off spacecraft and instruments going to space is to build them in clean rooms, such as this one at JPL.  These large rooms with filtered air do help lower the count of microbes on surfaces, but the bacteria are everywhere and further steps are essential.  (NASA/JPL-Caltech)

As he later elaborated to me, other “wicked” risk-benefit problems include gene editing and autonomous driving — both filled with great potential and serious potential downsides.  Like travel to other planets and moons.

“This is subjective,” Maynard said, “but I’d put planetary protection on the more wicked end of the spectrum. It combines individual priorities and ethics  — what people and groups deeply believe is right — with huge uncertainties.  That makes it something never really experienced before and so escalates all factors of wickedness.”

Those groups include scientists (who very much don’t want Mars or another potentially habitable place to be contaminated with Earth life before they can get there), to advocates of greater space exploration (who worry that planetary protection will slow or eliminate some missions they very much want to proceed), to NASA mission managers (worried about delays and costs associated with planetary protections surprises.)

And then there’s the general public which might (or might not) have entirely different ethical concerns about the potential for contaminating other planets and moons with Earth life.

No wonder the problem is deemed wicked.

We’ll get into the pros and cons, but first some background:

I asked NASA’s Planetary Protection officer, Catharine Conley, whether Earth life has been transported to its most likely solar system destination, Mars.

Her reply:  “There are definitely Earth organisms that we’ve brought to Mars and are still alive on the spacecraft.”

Catharine “Cassie” Conley has been NASA’s Planetary Protection officer since 2006. There is only one other full-time official in the world with the same responsibilities, and he works for the European Space Agency. (NASA/W. Hrybyk)

She said it is quite possible that some of those organisms were brushed off the vehicles or otherwise were shed and fell to the surface. Because of the strong ultraviolet radiation and the Earth life-destroying chemical makeup of the soil, however, it’s unlikely the organisms could last for long, and equally unlikely that any would have made it below the surface.  Nonetheless, it is sobering to hear that Earth life has already made it to Mars.

Related to this reality is the understanding that Earth life, in the form of bacteria, algae and fungi and their spores, can be extraordinarily resilient.  Organisms have been discovered that can survive unimagined extremes of heat and cold, can withstand radiation that would kill us, and can survive as dormant spores for tens of thousands of years.

What’s more, Mars scientists now know that the planet was once much warmer and wetter, and that ice underlies substantial portions of the planet. There are even signs today of seasonal runs of what some scientists argue is very briny surface water.

So the risk of Earth life surviving a ride to another planet or moon is probably greater than imagined earlier, and the possibility of that Earth life potentially surviving and spreading on a distant surface (think the oceans of Europa and Enceladus, or maybe a briny, moist hideaway on Mars) is arguably greater too.  From a planetary protection perspective, all of this is worrisome.

The logic of planetary protection is, like almost everything involved with the subject, based on probabilities.  Discussed as far back as the 1950s and formalized in the 1967 Outer Space Treaty, the standard agreed on is to take steps that ensure there is less than a 1 in 10,000 chance of a spaceship or lander or instrument from Earth bringing life to another body.

This figure takes into account the number of microorganisms on the spacecraft, the probability of growth on the planet or moon where the mission is headed, and a series of potential sanitizing to sterilizing procedures that can be used.  A formula for assessing the risk of a mission for planetary protection purposes was worked out in 1965 by Carl Sagan, along with Harvard theoretical physicist Sidney Coleman.

Deinococcus radiodurans is an extremophilic bacterium, one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and is therefore known as a polyextremophile and is considered perhaps the world’s toughest bacterium. It can withstand a radiation dose 1,000 times stronger than what would kill a person.

A lot has been learned since that time, and some in the field say it’s time to re-address the basics of planetary protection.  They argue, for instance, that since we now know that Earth life can (theoretically, at least) be carried inside a meteorite from our planet to Mars, then Earth life may have long been on Mars — if it is robust enough to survive when it lands.

In addition, a great deal more is known about how to sanitize a space vehicle without baking it entirely — a step that is both very costly and could prove deadly to the more sophisticated capsules and instruments.  And more is known about the punishing environment on the surface of Mars and elsewhere.

People ranging from Mars Society founder Robert Zubrin to Cornell University Visiting Scientist Alberto G. Fairén in Nature Geoscience have argued — and sometimes railed — against planetary protection requirements. NASA mission managers have often voiced their concerns as well.  The regulations, some say, slow the pace of exploration and science to avoid a vanishingly small risk.

Brent Sherwood, planetary mission formulation manager for JPL, is currently overseeing two proposed projects for New Frontiers missions.  One is to search for signs of life on Saturn’s moon Enceladus and the other for habitability on the moon Titan. (Brent Sherwood)

Brent Sherwood, program manager for solar system mission formulation at JPL, spoke at AbSciCon about what he sees as the need for a review and possibly reassessment of the planetary protection rules and regulations.  As someone who helps scientists put together proposals for NASA missions in the solar system, he has practical and long considered views about planetary protection.

He and his co-authors argue that the broad conversation that needs to take place should include scientists, ethicists, managers, and policy makers; and especially should include the generations that will actually implement and live with the consequences of these missions.

In the abstract for his talk, Sherwood wrote:

“The (1 chance in 10,000) requirement may not be as logically sound or deserving of perpetuation as generally assumed.  What status should this requirement have within an ethical decision-making process? Do we need a meta-ethical discussion about absolute values, rather than an arbitrary number that purports to govern the absolute necessity of preserving scientific discovery or protecting alien life?”

As he  later he told me: “I’m recommending that we be proactive and engage the broadest possible range of stakeholder communities…. With these big, hairy risk problems, everything is probabilistic and open to argument.  People are bad at thinking of very small and very big numbers, and the same for risks.  They tend to substitute opinion for fact.”

Sherwood is no foe of planetary protection.  But he said planetary protection is a “foundational” part of the space program, and he wants to make sure it is properly adapted for the new space era we are entering.

Elon Musk of SpaceX, Jeff Bezos of Blue Origins and NASA have all talked about potentially sending astronauts to Mars or establishing a colony on Mars in the decades ahead.  Many obstacles remain, but planning is underway. (Bryan Versteeg/

Planetary protection officer Conley contends that regular reviews are already built into the system.  She told me that every mission gets a thorough planetary protection assessment early in the process, and that there is no one-size-fits-all approach.  Rather, the risks and architecture of the missions are studied within the context of the prevailing rules.

In addition, she said, the group that oversees planetary protection internationally — the Committee on Space Research (COSPAR) — meets every two years and its Panel on Planetary Protection takes up general topics and welcomes input from whomever might want to raise issues large or small.

“You hear it said that there are protected areas on Mars or Europa where missions can’t go, but that’s not the case,” she said.  “These are sensitive areas where life just might be present now or was present in the past.  If that’s the case, then the capsule or lander or rover has to be sterilized to the level of the Viking missions.”

She said that she understood that today’s spacecraft are different from Viking, which was designed and built from scratch with planetary protection in mind.  Today, JPL and other mission builders get some of their parts “off the shelf” in an effort to make space exploration less expensive.

“We do have to balance the goals of exploration and space science with making sure that Earth life does not take hold.  We also have to be aware that taxpayer money is being spent.  But if a mission sent out returns a signal of life, what have we achieved if it turns out to be life we brought there?

“I see planetary protection as a great success story.  People identified a potential contamination problem back in the ’50s, put regulations into place, and have succeeded in avoiding the problem.  This kind of global cooperation that leads to the preventing of a potentially major problem just doesn’t happen that often.”

The global cooperation has been robust, Conley said, despite the fact that only NASA and the European Space Agency have a full-time planetary protection officer.  She cited the planning for the joint Russian-Chinese mission to the Martian moon Phobos as an example of other nations agreeing to very high standards.  She and her European Space Agency (ESA) counterpart traveled twice to Moscow to discuss planetary protection steps being taken.

Andrew Maynard is the director of Arizona State University’s Risk Innovation Lab and is a professor in School for the Future of Innovation in Society.  (ASU.)

So far, she said private space companies have been attentive to planetary protection as well.  Some of the commercial space activity in the future involves efforts to mine on asteroids, and Conley said there is no planetary protection issues involved.  The same with mining on our moon.

But should the day arrive that private companies such as SpaceX and Blue Origin seriously propose a human mission to Mars — as they have said they plan to — Conley said they would have the same obligations as any NASA mission.  The US has not yet determined how to ensure that compliance, she said, but companies already would need Federal Aviation Administration approval for a launch, and planetary protection is part of that.

Risk innovation expert Maynard, however, was not so sure about those protections.  He said he could imagine a situation where Elon Musk of SpaceX or Jeff Bezos of Blue Origin or any other space entrepreneur around the world would decide to move their launch to a nation that would be willing to provide the service without intensive planetary protection oversight.

“The risk of this may be small, but this is all about the potentially outsize consequences of small risks,” he said.

Maynard said that was hardly a likely scenario — and that commercial space pioneers so far have been supportive of planetary protection guidelines — but that he was well aware of the displeasure among some mission managers and participating scientists about planetary protection requirements.

Given all this, it’s easy to see how and why planetary protection advocates might feel that the floodgates are being tested, and why space explorers looking forward to a time when Mars and other bodies might be visited by astronauts and later potentially colonized are concerned about potential obstacles to their visions.

An artist’s rendering of a sample return from Mars.  Both the 2020 NASA Mars mission and the ESA-Russian mission are designed to identify and cache intriguing rocks for delivery to Earth in the years ahead. (Wickman Spacecraft & Propulsion)

This column has addressed the issue of “forward contamination” — how to prevent Earth life from being carried to another potentially habitable solar system body and surviving there.  But there is another planetary protection worry and that involves “backward contamination” — how to handle the return of potentially living extraterrestrial organisms to Earth.

That will be the subject of a later column, but suffice it to say it is very much on the global space agenda, too.

The Apollo astronauts famously brought back pounds of moon rocks, and grains of asteroid and comet dust have also been retrieved and delivered.  A sample return mission by the Russian and Chinese space agencies was designed to return rock or grain samples from the Martian moon Phobos earlier this decade, but the spacecraft did not make it beyond low Earth orbit.

However, the future will see many more sample return attempts.  The Japanese space agency JAXA launched a mission to the asteroid 162173 Ryugu in 2014 (Hayabusa 2) and it will arrive there next year.  The plan is to collect rock and dust samples and bring them back to Earth.  NASA’s OSIRIS-REx is also making its way to an asteroid, 101955 Bennu, with the goal of collecting a sample as well for return to Earth.

And in 2020 both NASA and ESA (with Russian collaboration) will launch spacecraft for Mars with the intention of preparing for future sample returns.  Sample return is a very high priority in the Mars and space science communities, and many consider it essential for determining whether there has ever been life on Mars.

So the “wicked” challenges of planetary protection are only going to mount in the years ahead.









Supernovae Give, And Can Take Away

What is likely the brightest supernova in recorded human history, SN 1006 lit up planet Earth’s sky in the year 1006 AD. The expanding debris cloud from the stellar explosion, still puts on a cosmic light show across the electromagnetic spectrum. The supernova is located about 7,000 light-years from Earth, meaning that its thermonuclear explosion actually happened 7,000 years before the present day.  Shockwaves in the remnant accelerate particles to extreme energies and are thought to be a source of the mysterious cosmic rays. NASA, ESA, Zolt Levay (STScI)

We live in a dangerous universe. We know about meteor and comets, about harmful radiation that could extinguish life without an electromagnetic shield, about major changes in climate that are both natural and man-made.

There’s another risk out there that some scientists assert could cause large-scale extinctions even though it would occur scores of light-years away.  These are supernovae – explosions of massive stars that both create and spread the heavy elements needed for life and send out high energy cosmic rays that can travel far and cause enormous damage.

As with most of these potential threats, they fortunately occur on geological or astronomical time scales rather than human ones. But that doesn’t mean they don’t happen.

At the recent Astrobiology Science Conference (AbSciCon) a series of talks focused on that last threat – starting with a talk on “When Stars Attack.”

And together five different presenters made a persuasive case that Earth was on the receiving end of a distant supernova explosion some two to three million years ago, and probably around 7 or 8 million years ago as well. The effects of the cosmic ray bombardment have been debated and disputed, but the evidence for the occurrences is based on the rock record and is now strong.

“The evidence is there on the ocean floor:  in rocky crusts, nodules and sediment,” said Brian Fields, professor of astronomy at University of Illinois.  “We’ve been able to date it and provide some idea of how far away the star blew up.”  The answer is between about 90 and 300 light-years.

Supernova 1994D exploded on the outskirts of disk galaxy, and outshines even the center of the galaxy. Supernovae may expel much, if not all, of the material away from a star,  at velocities up to 30,000 km/s or 10% of the speed of light. This drives an expanding and fast-moving shock wave into the surrounding interstellar medium that, if close to Earth (or any other planet) can have dire consequences.  Supernovae also create, fuse and eject the bulk of the chemical elements produced by nucleosynthesis, the heavier elements needed to form planets and later make possible life.  ( High-Z Supernova Search Team, HST, NASA)

“Supernova explosions happen all the time– on average every 30 years in our galaxy, though they are most often distant and obscured from view,” Fields said.  “They generate cosmic rays that can spread through the galaxy for 30 million years.  These are the cosmic rays that make carbon-14 and can threaten astronauts in space.  But that’s not what we’re focused on — we look at the ones that are close to us and could have a far more dramatic effect, and they are pretty rare.”

What is deemed to be the “kill zone” for a planet nearby a supernova is 30 light-years; the high energy particles from an explosion that close would, he said, likely end all or most life on Earth by setting into motion a variety of atmospheric and surface changes. Fields there is no evidence of such a close and damaging supernove within the past 10 million years, the period that has been studied with some rigor.

But because a close supernova explosion hasn’t happened recently doesn’t mean that it didn’t happened during earlier times.  Or that it couldn’t happen in the far future.

“By nailing the signal of a close but not ‘kill zone’ supernova two to three million years ago, and most likely another at 7 to 8 million years ago, we make the case that supernova can and do have significant effects on Earth.”

The community of scientists who study supernovae and their effects on Earth, both potential and known, is small, and has been most active in the past decade.  There was an earlier time when scientists focused on supernovae as the potential cause for the massive dinosaur extinction, but the field shrank with confirmation in 1990 that a six-mile wide meteor landed on Mexico’s Yucatan Peninsula about 65 million years ago and was the likely cause of the global extinction.

Brian Fields, chair of the astronomy department at the University of Illinois and a professor of physics, focuses on cosmology, nuclear and particle astrophysics and astrobiology as well as supernovae — especially those of the near-Earth variety. (University of Illinois)

But now, with the advent of new theories and some very high tech and precise measuring the field and subject has come to life, with research nodes in Germany, Australia and the American Midwest.

The key to understanding the effects of distant supernovae on Earth involves a radioactive isotope of iron, iron-60.  It’s one of the many elements known to be sent into the cosmos by the massive thermonuclear blasts that define a supernova, that send out shock waves capable of spurring the formation of new stars as well as providing the universe with the heavier chemical elements needed to form everything from planets to genes.

It was the young Fields and colleagues who theorized some two decades ago that iron-60 could be a telltale sign of a relatively nearby supernova.  He told me that no other significant sources of iron-60 are known to exist, and so if it were found on Earth scientists would know where it came from.

With a half-life of some three million years, the iron-60 would be a potentially strong signal for that length of time and and then a weaker but potentially detectable signal after that.

The question was how do you find iron-60 on Earth? The answer came from the bottom of the ocean.

First in 1999 a group from the Technical University of Munich in Germany identified some iron-60 in iron-manganese crustal rocks at the bottom of the Pacific, and then in 2013 reported finding the telltale isotope in not only rocks but also in nodules and most important in fossil bacteria and sea-floor sediments.  They used ultra-sensitive accelerator mass spectrometry to isolate and identify the iron-60, which they reported was deposited some 1.6 to 3 million years ago.

These are transmission electron microscope images showing tiny magnetofossils containing iron-60, a form of iron produced during the violent explosion and death of a massive star in a supernova. They were deposited by bacteria in sediments found on the floor of the Pacific Ocean.© Marianne Hanzlik, Chemie Department, FG Elektronenmikroskopie, Technische Universität München

Last year as well the Australian group, led by Anton Wallner of the Australian National University, found the iron-60 to be deposited globally and to have arrived within the same general time frame.  And Gunther Korschinek, a physicist at the Technical University of Munich involved in the initial German iron-60 detections, led a team that found elevated amounts of iron-60 in lunar soil samples brought from to moon back to Earth during the Apollo program.

As Fields put it, the studies together gave a clear signal of a supernova explosion, or series of explosions, at 2 to 3 million years ago, and a less clear but likely signal of the same at 7 to 8 million years ago.

Since Fields and other scientists were presenting during the AbSciCon conference, the talks not surprisingly focused on potential biological implications of supernova explosions.  And while supernova impacts on the biosphere are not particularly well understood, a number of intriguing theories were presented.

Brian Thomas of Washburn University described how cosmic rays from close supernova would significantly increase levels of electrically charged elements and molecules in the atmosphere, lasting thousands of years.  In the upper atmosphere this would have the effect of setting into motion a chemical cascade that would deplete stratospheric ozone. In the lower atmosphere, the effect would likely be changes in climate and minor mass extinctions.

The “holy grail” of their supernova work is matching a detected one with a dramatic event in the Earth biosphere, most especially a mass extinction.  The 2 to 3 million years ago period includes the boundary between the Pleistocene and Pliocene epochs, when Earth climate changed and major glaciations periods began — possibly supernova-related changes but not the extreme change a close supernova could produce.

Another potential effect of the supernova event of 2 to 3 million years ago is increased rates of mutation and of lightning, and thus forest fires on Earth.

Adrian Melott of the University of Kansas suggested that expected mutations from radiation sources such as supernovae could explain evolutionary changes in a variety of groups of organisms and creatures during that period — as a result of increased deadly cancers in some species and increased positive mutations in others.

He also said that evidence of more widespread wildfires during that long period — as measured in charcoal deposits — could be the result of increased cloud to ground lightning induced by the additional high-energy particle environment created by a relatively close supernova explosion.

The Crab nebula – one of the most glorious images produced by the Hubble Space Telescope — is the remnant of supernovae explosions that occurred at a distance of some  6,700 light-years.  The very bright light of the explosion was noted in 1054 and remained visible for around two years. The event was recorded in contemporary Chinese astronomy, and references to it are also found in a later (13th-century) Japanese document,  perhaps in pictograph associated with the Anasazi people of the Southwest.  The supernova, SN 1054 has been widely studied and is often considered the best known supernova in astronomy.  (NASA).

The iron-60 signatures of a close supernova have been a great boon to the field, but they do not go back beyond that almost 10 million year period when the radioactivity was present.  To go back further than that, Fields said different radioactive signatures would be needed — and not those that go back to the formation of the planet.

“It’s a hard problem because nature has been unkind,”  he said.  “The early mass extinctions – 100 million and more years ago – need radioactivity that lasts that long.  And the only element we’ve found is plutonium-244, which is not stable in any form.”

Plutonium-244 has a half life of 80 million years, and so could potentially be used to identify close supernova explosions in a manner similar to iron-60, but during that much longer time frame.  And as Fields explained it, plutonium-244 is produced in a few dramatic ways:  during the explosion of a nuclear bomb, the explosion of a supernova, or the merging of a pair of neutron stars.”

Although the science around the formation and detection of plutonium-244 in nature is immature, he said it remains the best pathway to find that “holy grail” — a known mass extinction directly associated with a close supernova explosion.


Supernovae can burn with a luminosity of ten billion suns. This show a before and after for supernova 1987A, which exploded in 1987 in the Large Magellanic Cloud (LMC), a nearby galaxy. (Australian Astronomical Observatory/ David Malin)











NASA Panel Supports Life-Detecting Lander for Europa; Updated

Artist conception of water vapor plumes coming from beneath the thick ice of Jupiter’s moon Europa. The plumes have not been definitively detected, but Hubble Space Telescope images make public earlier this month appear to show plume activity in an area where it was detected once before.  How will this finding affect decision-making about a potential NASA Europa lander mission? (NASA)

As I prepare for the Astrobiology Science Conference (Abscicon) next week in Arizona, I’m struck by how many speakers will be discussing Europa missions, Europa science, ocean worlds and habitability under ice.  NASA’s Europa Clipper mission to orbit that moon, scheduled for launch to the Jupiter system in the mid 2020s, explains part of the interest, but so too does the unsettled fate of the Europa lander concept.

The NASA Science Definition Team that studied the Europa lander project will both give a science talk at the conference and hold an afternoon-long science community meeting on their conclusions.  The team argued that landing on Europa holds enormous scientific promise, most especially in the search for life beyond Earth.

But since the Europa lander SDT wrote its report and took its conclusions public early this year, the landscape has changed substantially.  First, in March, the Trump Administration 2018 budget eliminated funding for the lander project.  More than half a billion dollars have been spent on Europa lander research and development, but the full project was considered to be too expensive by the White House.

Administration budget proposals and what ultimately become budget reality can be quite different, and as soon as the Europa lander was cancelled supporters in Congress pushed back.  Rep. John Culberson (R-Tex.) and chair of the House subcommittee that oversees the NASA budget, replied to the proposed cancellation by saying “NASA is a strategic national asset and I have no doubt NASA will receive sufficient funding to complete the most important missions identified by the science community, including seeking out life in the oceans of Europa.”

More recently, researchers announced additional detections of plumes of water vapor apparently coming out of Europa — plumes in the same location as a previous apparent detection.  The observing team said they were confident the difficult observation was indeed water vapor, but remained less than 100 percent certain.  (Unlike for the detection of a water plume on Saturn’s moon Enceladeus, which the Cassini spacecraft photographed, measured and flew through.)

So while suffering a serious blow in the budgeting process, the case for a Europa lander has gotten considerably stronger from a science and logistics perspective.  Assuming that the plume detections are accurate, a lander touching down in that general area would potentially have some access to surface H20 that was in the vast global ocean under the ice not too long ago.

Science fiction writer and proto-astrobiologist Arthur C. Clarke famously wrote decades ago that the first life found beyond Earth would most likely be in the oceans of Europa.  In the early 1980s he wrote a sequel to “2001:  A Space Odyssey” called “2010:  Odyssey Two”, with life under the ice of Europa central to the plot.

At the climactic moment in the novel, the hero returns to the iconic computer HAL which sends out this message:


Hopefully Congress and the White House, if not HAL, can be persuaded otherwise.

Here is a column I wrote about the Europa lander SDT in February:


Artist rendering of a potential life-detecting lander mission to Europa that would follow on the Europa Clipper orbiter mission. In the background is Jupiter. NASA/JPL/Caltech

It has been four long decades since NASA has sent an officially-designated life detection mission into space.  The confused results of the Viking missions to Mars in the mid 1970s were so controversial and contradictory that scientists — or the agency at least — concluded that the knowledge needed to convincingly search for extraterrestrial life wasn’t available yet.

But now, a panel of scientists and engineers brought together by NASA has studied a proposal to send a lander to Jupiter’s moon Europa and, among other tasks, return to the effort of life-detection.

In their recommendation, in fact, the NASA-appointed Science Definition Team said that the primary goal of the mission would be “to search for evidence of life on Europa.”

The other goals are to assess the habitability of Europa by directly analyzing material from the surface, and to characterize the surface and subsurface to support future robotic exploration of Europa and its ocean.

Scientists agree that the evidence is quite strong that Europa, which is slightly smaller than Earth’s moon, has a global saltwater ocean beneath its deep ice crust, and that it contains twice as much water as exists on Earth.

For the ocean to be liquid there must be substantial sources of heat — from tidal heating based on the shape of its orbits, or from heat emanating from radioactive decay and entering the ocean through hydrothermal vents.  All could potentially provide an environment where life could emerge and survive.

Kevin Hand of the Jet Propulsion Laboratory is a specialist in icy worlds and is deputy project scientist for the Europa project.  He was one of the co-chairs of the Science Definition Team (SDT) and he said the group was ever mindful of the complicated history of the Viking missions.  He said that some people called Viking a “failure” because it did not clearly identify life, but he described that view as “entirely unscientific.”

“It would be misguided to set out to ‘find life’,” he told me.  “The real objective is to test an hypothesis – one we have that if you bring together the conditions for life as we know them, then they might come together and life can inhabit the environment.

“As far as we can tell, Europa has the water, the elements and the energy needed to create a habitable world.  If the origin of life involves some relatively easy processes, then it just might be there on Europa.”

This artist’s rendering shows NASA’s Europa orbiter mission spacecraft, which is being developed for a launch sometime in the 2020s. The mission would place a spacecraft in orbit around Jupiter in order to perform a detailed investigation of the planet’s moon Europa. The spacecraft will arrive at Jupiter after a multi-year journey, orbiting the gas giant every two weeks for a series of 45 flybys of Europa. NASA generally sends orbiters to a planet or moon before sending a lander. (NASA)

The conclusions of the SDT team, which is made is up of dozens of scientists and engineers, will set the stage for further review, rather than for immediate action.  The report goes to NASA, where it is assessed in relation to other compelling and competing missions.  Both the Congress and White House can and do weigh in

If it is approved, the Europa lander mission would be a companion to the already funded Europa multiple flyby mission scheduled to launch in the 2020s.  While that spacecraft, the Europa Clipper, would have some capacity to determine whether or not the icy moon is habitable, a lander would be needed to search for actual signs of life.

A mission to Europa was a top priority of the 2010 Decadal Review, a synthesis of potential projects in various disciplines that is reviewed by the National Research Council of the National Academy of Sciences.

Kevin Hand of JPL, the deputy science
lead for the Europa project.

Its recommendations from the Decadal Review are generally followed by NASA.  It remains unclear whether the Europa lander is a natural follow-on to the Europa Clipper or a new initiative to be judged on its own.  But the project does have strong support — last year Rep. John Culberson (R-Tex.) pushed a bill through Congress making it illegal to not send a lander to Europa.

Although there are many hurdles to clear for the Europa lander, the SDT report is nonetheless a rather momentous event since it strongly recommends a life-detection mission.  So I thought it was worthwhile to include the entire preface of the team’s conclusions.

“The Europa Lander Science Definition Team Report presents the integrated results of an intensive science and engineering team effort to develop and optimize a mission concept that would follow the Europa Multiple Flyby Mission and conduct the first in situ search for evidence of life on another world since the Viking spacecraft on Mars in the 1970s.

The Europa Lander mission would be a pathfinder for characterizing the biological potential of Europa’s ocean through direct study of any chemical, geological, and possibly biological, signatures as expressed on, and just below, the surface of Europa. The search for signs of life on Europa’s surface requires an analytical payload that performs quantitative organic compositional, microscopic, and spectroscopic analysis on five samples acquired from at least 10 cm beneath the surface, with supporting context imaging observations.

This mission would significantly advance our understanding of Europa as an ocean world, even in the absence of any definitive signs of life, and would provide the foundation for the future robotic exploration of Europa.”

(Here is the full Europa lander SDT report.)

Europa is slightly smaller than the size of our moon, and is broadly agreed to have a large ocean under its 10 to 15 miles ice crust. It orbits Jupiter every 3.5 days. That promixity, coupled with the fact that Europa has a slightly elliptical rather than circular orbit, create the tidal “flexing” and thus heating that can keep water liquid. (NASA)

Hand said that a lander would be a natural complement to the Europa Clipper, which is being designed to orbit Jupiter and pass by Europa 45 times at altitudes varying from 1675 miles to 16 miles.  The flybys, he said, could potentially identify cracks and fissures in the crust of the moon, and thereby help identify where a lander should touch down.

What’s more, images taken by the Hubble Space Telescope in 2012 suggest that Europa may be spitting out water in plumes that those clearly detected on Saturn’s moon, Enceladus.

“If a plume was identified during a flyby, you better believe that we would do all we could to land somewhere close to it.  The goal is to get as near as possible to the water coming out from under the crust because that’s how we’ll best learn whether that water has complex organic molecules, nitrogen compounds needed for life and possibly life itself.”

If the lander project does get the green light in the months (or years) ahead, NASA would then put out a call to propose instruments that could search for the various chemical building blocks and manifestations life, as well morphological signs that life once was present.  The search for life, in other words, would involve checking the boxes of building blocks or known molecular signs of possible life as they are found (or not found.)

This is quite a different approach from that used during the Viking missions.

Famously, the so-called “Labelled Release” experiments on both Viking 1 and Viking 2 met the criteria for having detected life as set out by NASA scientists before the mission began.  Those criteria involved the detection of metabolism, the chemical processes that occur within a living organism in order to maintain life.  A detection would imply the presence of life right on the harsh, irradiated Martian surface.

In the LR experiment, a drop of very dilute aqueous nutrient solution was dropped into a sample collected of Martian soil. The nutrients (seven molecules that were products of the Miller-Urey experiment) were tagged with radioactive carbon 14 and the air above the soil was monitored for the evolution of radioactive CO2 gas.  The presence of the gas was interpreted as evidence that microorganisms in the soil had metabolized one or more of the nutrients.

A picture of the Martian surface, as seen by NASA’s Viking 2 lander in 1976.

The LR was followed with a control experiment, and the results consistently met the criteria for having detected “life.”  Two other biology experiments on Viking,  however, came up negative, including the one considered most conclusive — that no carbon-based organic material was detected in the soil, except for one interpreted as contamination from Earth.

Subsequent Mars missions have strongly suggested that those organics interpreted as contamination were, in fact, organics interacting with perchlorate molecules now known to be common on the Martian surface.  But despite this revision, the Mars science community remains broadly skeptical of the Labelled Release results, arguing that the CO2 could have been produced without biology.  That, however, has not stopped LR principal investigator Gilbert Levin, and some others, from arguing now for forty years that the experiment did find life, creating  a controversy that NASA has long struggled with.

Hand said that in hindsight, “we can see that it didn’t make sense to look for metabolism until we knew a lot more.  We need to follow the water, follow the carbon, follow the nitrogen, follow the complex molecules, and if all of that succeeds then we look for a living, breathing creature.”

One of the inspirations for the hypothesis that Europa might harbor life under and within its ice is the recognition that frozen Antarctica also is home to microbial life.  The most significant laboratory is Lake Vostok, an enormous collection of water beneath more than two miles of Antarctic ice.

Researchers have determined that microbial life exists miles down through the ice.  The distribution is small — something like 100 cells per milliliter of melted ice — but researchers have been trying for years to drill down into the lake and determine if the lake itself is home to more abundant life.  The research has been done primarily by Russian scientists and engineers, and has been slowed by the harsh conditions and innumerable technical problems.

Three dimensional model of Lake Vostok drilling. (National Science Foundation)

But as a proof of concept, Hand said, Lake Vostok and other subglacial lakes in Antarctica show that life can survive in freezing conditions.  He said the science teams recommended that any life detection instrument that might go to Europa be able to identify life in the very low concentrations found at Vostok.

Tori Hoehler, a research scientist at NASA’s Ames Research Center, is a specialist in microbial life in low energy environments (like Vostok and perhaps Europa,) and he is also a member of the Europa lander science definition team.

“Our present understanding of Europa suggests that it is habitable, but it is more difficult to constrain how abundant or productive a Europan biosphere — should one exist — might be.  For that reason, a conservative approach is to look to some of Earth’s most sparsely populated ecosystems when setting measurement targets for the lander.”

But however low that abundance might be, the detection of anything with characteristics of life on Europa would be a huge advance for science.