Forward Contamination of Mars

Mars illustration

Submitted by Esma Bozlak to fulfill the ethics in science requirement for the Young Scientist Program at BMSIS.

Mars has attracted the attention of scientists from the past to present, and going to Mars to explore with robots as well as with humans has been of interest to many people. Many successful, as well as unsuccessful, Mars missions have been attempted since the beginning of the space age. The first successful launch was done with Mariner 4 in 1964. It was the spacecraft that took the first photographs of another planet from space (1). Since Mariner 4, many other spacecraft have been sent to Mars, with three missions being launched in less than two weeks in 2020 alone. There are 61 missions in total, both successful and unsuccessful, that have been sent to Mars. Through these missions, some questions that have been posed are: “What if those spacecraft have carried terrestrial organisms to Mars?”; “If this has been the case, could they have survived in Martian conditions?”; and “How do we protect the Red Planet from this kind of contamination (or, even, should we do so)?”* Everything we’ve learned about Mars suggests that the planet may once have been able to host ecosystems (if life ever did arise there), and Mars may even still be an incubator for life today. Research suggests that Mars once had abundant liquid water at its surface, a warmer and thicker atmosphere, and, because of these features, it could have been a potentially habitable environment (2). If Mars ever did have life, or currently has life, should we do our best to avoid forward contamination that may then affect that life and/or our ability to detect it?

What is Forward Contamination?

The number of Mars missions continues to increase and this has, in turn, increased the risk of the biological contamination of Mars. However, microorganisms that are potential contaminants on the Martian surface may be exposed to a variety of harmful conditions, both during travel to Mars as well as on the Martian surface itself. During the transit in space, these microorganisms will have been exposed to the space environment, which can damage cells severely and causes dehydration, exposure to low temperature, and increased exposure to solar UV radiation. Then, on the Martian surface, there are sandstorms covering everything in dust and the temperature difference between day and night is very high. Also, Mars does not have an ozone layer or magnetic field to help shield from harmful UV and other radiation. However, cells may still be transported to the ground from the surface of the spacecraft and it is a possibility for those microorganisms, once on the Martian surface, that they may come into contact with the dust and be disseminated over long distances during dust storms (4).

The organic chemicals produced by the emerging life are unique to the biosignatures of living or ancient indigenous life. If contamination occurs, life is no longer specific to that area. From this point of view, there are two types of contamination: forward contamination and backward contamination. Contamination of another planetary body with living organisms or biological material from the Earth is called forward contamination. This contamination has the potential to override future scientific discoveries by disrupting other planetary environments or potential endogenous ecosystems. Meanwhile, backward contamination involves the potential for harmful contamination of the Earth as well as the spacecraft and habitats of human missions, with possible immediate and long-term effects on the health of astronauts (3).

Ethical Stances with Regard to the Forward Contamination of Mars

The question of whether we should care about the forward contamination of Mars is discussed below with regard to the major approaches to ethics.


A deontological ethical system is one based upon a rule or set of rules, such that one assesses the rightness or wrongness of an action according to whether or not it is consistent with a particular ruleset.
Is forward contamination on Mars important to planetary protection? There are two possible views that I foresee from a deontological point of view: In the first approach, one may argue ‘No, it is not important, this solar system is for everyone, Earth or Mars does not matter. We have to investigate other planets and for this, we need to send rovers to other planets. It is possible that signs of ancient or even extant life are on Mars to be found, but to be sure about that we need to explore Mars with rovers.’ However, in a second approach based on ethical rules, one may argue, ‘Yes, it is important, we should protect Mars from forward contamination. If life has already occurred, it could be damaged by contamination. Trying to explore life, we could change the nature of the planet and maybe that could cause life on that planet to perish.’


A consequentialist ethical system judges the rightness or wrongness of an action based upon the resulting consequences. Consequentialism compares the relative desirability of all the various options and selects the action that leads to the best foreseeable results.

When rovers are sent to Mars, it can be argued that the exploration and discovery will be beneficial for humanity. Thus, consequently, Mars missions will be useful for the knowledge to be gained and this is ethically important when the risk of contamination is avoided as much as possible. For example, thanks to missions such as InSight, we have learned that Mars was geologically for much of its history. If we hadn’t taken the risk of contamination and sent such missions, we wouldn’t have reached this important result.

Virtue Ethics

A system based on virtue ethics considers the role of a person’s character in making decisions. Virtue ethics suggests that personal adherence to virtuous qualities provides a basis for making decisions. Those who think it is morally wrong to destroy the habitats of potential forms of life on Mars (or to potentially negatively affect any living Martian beings) through biological contamination with Earth life are using the ethics of virtue to oppose the forward contamination of Mars. However, people with this ethical approach may also claim that the knowledge people gain as a result of tasks is important in terms of science and is thus a virtuous behavior, favoring instead to risk the biological contamination of Mars for the return in scientific knowledge.


Because of the concerns for the forward contamination of Mars, some space agencies have applied stringent sterilization and cleaning of spacecraft. For instance, NASA has applied such sterilization methods on the Viking spacecraft that landed on the Martian surface successfully in 1975 (1). NASA has also taken various measures against contamination risk on all subsequent space missions (4). Although we know that we still cannot completely sterilize our spacecraft, efforts are being made to sterilize them as much as possible. These policies are based on the consequentialist approach that polluting the area makes exploring there more difficult and the results of experiments inaccurate. But there are still people who oppose planetary protection because they think the costs outweigh the risks. We have to organize space missions to learn about the planetary history of Mars, to explore it. However, when we get this information, we need to take into account the risk of contamination and reduce it to as low as possible.


3), Planetary protection for human exploration of Mars
4) Assessment of the Forward Contamination Risk of Mars by Clean Room Isolates from Space-Craft Assembly Facilities through Aeolian Transport – a Model Study ,

*Most of the information in this section was written using an essay that was written by me and Nehir Altan during an internship at Aarhus University, Institute of Bioscience.

Esma Bozlak is a graduate of Hacettepe University and is currently a Masters student in molecular biology and genetics at Izmir Institute of Technology (IZTECH). She is also a Research Associate with the Young Scientist Program at BMSIS.