Planetary Protection:
Ethical Implications of Evidence of Life on Mars
Planetary Protection: Ethical Implications of Evidence of Life on Mars
Journal of Astrobiology and Space Science Reviews, 1, 363-368, 2019

Planetary Protection: Ethical Implications of Evidence of Life on Mars
Ian Stoner
Saint Paul College


This commentary argues that the reviewed evidence for life on Mars places ethical constraints on future Mars missions. In order to conserve Mars’s scientific value, the international community should tighten planetary protection protocols and ban crewed missions to the surface of Mars.

Key Words: Mars, Planetary Protection

1. Introduction

Joseph et al (2019). review a range of evidence in support of two claims: that there is already life on Mars, and that a variety of microorganisms endemic to Earth can survive on, or just below, the surface of Mars. The evidence for the second claim is strong. The evidence for the first is suggestive, but we should take it seriously. Taking that evidence seriously has ethical implications that should shape space policy. In this commentary I argue that the reviewed evidence for Martian life suggests that the international community should tighten standards of planetary protection for Mars, including enforcing an indefinite pause on all plans to send crewed missions to the surface. I close by asking readers interested in astrobiology to be more assertive in explaining and defending the scientific value of Mars.

2. Background

Joseph et al. (2019) survey the evidence in support of several claims related to the possibility of life on Mars. Some of these claims are more robustly supported than others. Simulation studies establish that a variety of Earth microorganisms can survive the Martian environment. There is thus substantial evidence of current life on Mars in the form of extremophile microbes we inadvertently sent there on probes. It is also likely that Earth life has previously traveled to Mars via ejecta from meteorite impacts, and it is possible that some microbes transmitted in this way could have survived the trip and reproduced on Mars. Mars displays seasonal fluctuations in atmospheric methane concentrations and Joseph et al. argue that biological processes are currently the best explanation of these fluctuations. That would imply Mars hosts not just isolated or dormant life, but some kind of limited ecosystem.

That is the descriptive background I assume for this commentary. In addition, I assume a value judgement I expect is widely shared among readers of this journal: Mars is scientifically valuable, and scientific value cannot be fully accounted in economic terms. The contributions Mars can make to our understanding of the universe and our place in it are worth pursuing, quite apart from market motives, because improving our understanding of the universe is itself good.

In any catalog of the exciting scientific questions Mars can potentially answer, biological questions loom large. If there is life on Mars, the discoveries that follow from it will almost certainly have important implications for biology, organic chemistry, ecology, philosophy, theology, and other academic disciplines. Such discoveries would almost certainly have social and political ramifications as well. There are few projects in basic science that are more scientifically valuable than the search for life on Mars.

3. Argument

Preserving Mars’s scientific value is a moral imperative. Human activities that would destroy Mars’s ability to answer centrally important scientific questions (or that would cavalierly risk such destruction) aren’t merely foolish and short-sighted, they are morally wrong. So will I argue in this section.

For lack of a better term, allow me to use “destructive scientific investigation” to identify any means of investigation of an object of scientific interest that alters the studied object in such a way that it forecloses the possibility of using that same object to answer other scientific questions. Some destructive scientific investigations are morally permissible, but scientists generally recognize moral constraints on the use of destructive techniques. I have elsewhere defended a principle that attempts to articulate the conditions of morally permissible destructive investigation (Stoner 2017: Section 3). The principle of scientific conservation holds that destructive investigation is morally permissible only when (1) it does not foreclose the possibility of future investigations the threatened object could support and (2) no adequate non-destructive alternatives are available.

This principle of scientific conservation is probably best explained and defended through examples.

Suppose there is a geologic question about beach formation that could only be answered by grinding and dissolving in acid 400 kilograms of sand from a Florida beach. If the scientific question and the means proposed to answer it are legitimate, this investigation is probably permissible, because the sand destroyed is a miniscule fraction of the sand on the beach, and so destroying that sample does not threaten the possibility of other research on that beach's sand.

Contrast that scenario with an exogeologic question that could only be answered by grinding and dissolving in acid all 400 kilograms of moon rock collected by the Apollo missions. In this case it doesn't matter if the scientific question and proposed means of exploration are legitimate. To pursue this research would be morally wrong, because it forecloses the possibility of future scientific investigations that could only be pursued using those rocks. Destructive investigation in this case is morally wrong because it fails to conserve the scientific value of those moon rocks, and if our imaginary exogeologists went ahead with their destructive investigation, they would deserve moral outrage from the rest of us.

Destructive investigation is also wrong in cases in which an adequate non-destructive alternative is available. For example, suppose exogeologists have a scientifically legitimate question they can only answer through the study of 100 grams of moon rock. They have two methods available to them. Method one is an entirely non-invasive imaging technique, after which they could return the sample to the archive for future research. Method two involves grinding the sample and dissolving it in acid. If they chose the destructive method (perhaps because it is somewhat cheaper, or more convenient, or faster) they would wrongfully destroy those rocks.

How does this principle of scientific conservation apply to Mars exploration? Mars is an object of significant scientific interest. We should be careful, when designing research programs, that we only pursue programs we can be confident will leave Mars in a condition in which it can potentially answer a broad range of future scientific questions. We should be careful to conserve Mars’s scientific value in anticipation of future scientific questions we have not yet thought of, or questions we do not yet have the technology to pursue. And we should be careful, too, to employ adequate non-destructive alternatives whenever they are available, never opting for destructive methods even if the destructive methods are somewhat cheaper, or more convenient, or faster.

The challenge for translating these relatively uncontroversial moral claims into science policy is that we cannot be sure what the effects of our presence on Mars will be. If we were certain that Mars does not and cannot host life, then most experiments we might reasonably propose to do there would pass the standard set by the principle of scientific conservation. If we were certain that Mars has its own ecosystems, and that microbes introduced from Earth would alter the functioning of those ecosystems, then the principle of scientific conservation would require stringent planetary protections including a ban on human explorers on the surface. (Note that it makes no difference whether the origin of Martian ecosystems can be traced to ejecta from Earth. An ecosystem on another planet is scientifically invaluable, regardless of its origin (Conley & Rummel 2013).)

Our actual epistemic position lies between these boundaries of certainty. We must, as always, make our plans under conditions of uncertainty. The greater the chance that Mars hosts life that could be disrupted by Earth life, the more powerful the moral case for strict planetary protection. Only if we were very confident that Mars has no life, and that the microbial life human explorers would inevitably introduce could not take hold there, could we permissibly send humans to the surface, or otherwise relax planetary protections.

The evidence reviewed by Joseph et al. is sufficient to establish that we are nowhere near the no-life end of the confidence spectrum. It is of course possible that the authors are wrong in some of the interpretations they endorse. They might, for example, be wrong that Martian life is the cause of observed changes in atmospheric methane. But until we can establish that they are systematically wrong, until we can confidently rule out the possibility of Martian life, missions that risk introducing new microorganisms to Mars are scientifically and morally irresponsible.

We have, in robotic probes carefully cleaned according to COSPAR’s planetary protection protocol, an adequate non-destructive method of scientific investigation. Those protections should not be relaxed. If anything, in light of growing evidence of the possibility of Martian life, the international science community has moral reason to tighten them. One appropriate amendment to planetary protection agreements would be an explicit ban on crewed missions to the surface of Mars, along with mechanisms of effective enforcement.

4. Plea

The current state of public discourse concerning Mars exploration is largely shaped by people who speak in terms of colonization and exploitation and show little interest in Mars’s scientific value (Billings 2017). Bas Lansdorp wants to film people on the surface of Mars to auction the broadcasting rights. Robert Zubrin wants to settle Mars to fulfill humanity’s alleged pioneer nature. Elon Musk wants to colonize Mars as a planetary refuge.

Some in the space sciences community have viewed industry supporters of space development as natural allies. Early in the present era of public/private partnerships, in which the the most prominent entities on the paying side of launch-services contracts were governments who were, in turn, funding basic science, the illusion of allyship was possible to maintain. As industrious developers turn their attention to Mars, the illusion of alliance should be shattered. Though the goals of space science and space development are not in principle in conflict, in practice they usually are (Schwartz 2019), and the plans of Zubrin, Musk, and the others undoubtedly threaten the scientific value of Mars.

The basic trouble is that from the perspective of colonizers, settlers, and exploiters, planetary protection is irrelevant. We can of course succeed in colonizing and exploiting Mars in the absence of planetary protection. The thing we cannot do successfully, in the absence of effective planetary protections, is to learn from Mars.

I hope space science advocates will be able to secure a more prominent position in the public discourse about space exploration. And I hope that if they do, they will be willing to draw a sharp contrast between the values they exhibit in their pursuit of knowledge and the values industry exhibits in its pursuit of development. Part of making the scientific case for Mars is making the case for robust planetary protection. But more fundamentally, making the scientific case for Mars requires a vocabulary of value that is currently missing from the public conversation.

Industry on Earth has standardly viewed ecological damage as part of economic progress. Scientists can model an alternative understanding of the relationship between ecological damage and progress. Destruction of potential Martian ecosystems constitutes the destruction of scientific value; learning from Mars and protecting it from us are not goals in tension with one another, they are goals that can only be met in tandem. On a potentially biotic Mars, it is clear as can be that environmental protection and scientific progress are mutually reinforcing values. That is a lesson we would do well to import to Earth.


Billings, L. (2017), Should Humans Colonize Other Planets? No. Theology and Science, 15(3): 321–332.

Conley, C. A. and Rummel, J. D. (2013), Appropriate Protection of Mars. Nature Geoscience, 6: 587–588.

Joseph, R. G, Dass, R. S., Rizzo, V., Cantasano, N. and Bianciardi, G. (2019), Evidence of Life on Mars? Journal of Astrobiology and Space Science Reviews, 1: 40–81.

Schwartz, J. S. J. (2019), Space Settlement: What’s the Rush? Futures, (forthcoming).

Stoner, I. (2017), Humans Should Not Colonize Mars. Journal of the American Philosophical Association, 3(3): 334–353.