Description: Discover whether life on Mars is really possible in 2026. An honest, science-based guide to what we know, what we don't, and what human settlement on Mars would actually require.
Humanity Has Always Asked Whether We Are Alone. Mars Is Where We Are Closest to an Answer.
Let me start with something that I find genuinely extraordinary when I sit with it properly.
Right now, as you read this, there are active robots on the surface of Mars. Not metaphorically. Not in science fiction. Actually, physically, on the surface of another planet, forty-four million to four hundred and one million kilometers away depending on where Earth and Mars are in their respective orbits.
NASA's Perseverance rover is driving across the floor of Jezero Crater — an ancient lake bed that dried up approximately three and a half billion years ago — collecting rock samples from sedimentary formations that may preserve evidence of microbial life that existed when Mars was warm and wet. Its companion helicopter Ingenuity has completed dozens of powered flights in Mars's thin atmosphere, becoming the first powered aircraft to fly on another world.
The Curiosity rover, which has been operating since 2012, is still driving across the Gale Crater, analyzing the chemical composition of rocks and soil, measuring radiation levels, and characterizing the environment that any future human visitor would need to survive.
And orbiting above them, multiple spacecraft from NASA, ESA, China, the UAE, and India are mapping the planet's surface, characterizing its atmosphere, and monitoring its magnetic field — collectively building a picture of a world that is simultaneously deeply alien and surprisingly familiar.
We are not merely theorizing about Mars anymore. We are studying it in extraordinary detail, with hardware we put there. And what we are finding is both more encouraging and more challenging than most public discussion of Mars colonization fully acknowledges.
This guide covers both dimensions honestly — the genuine scientific basis for believing Mars could support life, the genuine challenges that make establishing that life extraordinarily difficult, and the honest current state of our knowledge about whether Mars has ever hosted life or could host it in the future.
Mars Then and Now — The Planet That Changed
To understand whether life on Mars is possible, you first need to understand what Mars was and what it became — because the gap between those two states is the central fact that shapes every dimension of the life-on-Mars question.
What Mars was approximately four billion years ago:
Mars was, in its early history, a remarkably different world from the frozen, thin-aired desert it is today. Evidence gathered from multiple Mars missions paints a consistent picture of an early Mars that was — for at least hundreds of millions of years — warm enough for liquid water to exist on its surface, wet enough for rivers to carve valleys and lakes to fill crater basins, and thick-atmosphered enough for water to persist rather than immediately freeze or evaporate.
The evidence for this ancient wet Mars is now extensive and robust. The Curiosity rover found ancient lake sediments in Gale Crater — rock formations that only form in the presence of standing liquid water over long periods. The Perseverance rover is driving across a fossil river delta in Jezero Crater. Mars's surface is covered in valley networks that could only have been carved by flowing water. Multiple orbital missions have identified hydrated minerals — clays and sulfates that form in the presence of liquid water — across Mars's ancient terrain.
For hundreds of millions of years, Mars had liquid water on its surface. And on Earth, everywhere we have found liquid water, we have found life. The implications of this parallel are significant.
What happened to Mars:
The transition from warm, wet Mars to the cold, thin-aired desert of today is one of planetary science's most significant questions. The most accepted explanation involves Mars's loss of its global magnetic field — which occurred approximately four billion years ago as Mars's smaller iron core cooled and its dynamo effect ceased.
A planet's magnetic field is its shield against the solar wind — the continuous stream of charged particles ejected by the Sun. Earth's magnetic field deflects most of this solar wind, preserving our atmosphere. Without a magnetic field, Mars's early thick atmosphere was gradually stripped away by the solar wind over millions and billions of years. As the atmosphere thinned, the greenhouse effect that had kept Mars warm diminished. Temperatures fell. Surface water froze or was lost to space. The planet transformed.
Mars today has an atmosphere approximately one percent as dense as Earth's — too thin to retain significant heat, too thin to provide meaningful protection from cosmic radiation, too thin to allow liquid water on the surface under most conditions. The average surface temperature is approximately negative sixty degrees Celsius, with extremes ranging from negative one hundred and twenty-five degrees at the poles in winter to approximately twenty degrees Celsius at the equator in summer.
This is the world we are asking whether life is possible on. Not the warm, wet Mars of four billion years ago — though we are also asking whether that ancient Mars hosted life — but the cold, thin, radiation-exposed Mars that exists today.
The Search for Past Life — What Perseverance Is Actually Doing
The Mars Sample Return mission — for which Perseverance is currently collecting samples — is designed specifically to answer the question of whether Mars ever hosted microbial life during its ancient warm, wet period.
Why ancient Mars is the best candidate:
The conditions of ancient Mars were, by the evidence we have gathered, genuinely habitable by the standards of Earth's early microbial life. Liquid water. A thicker, warmer atmosphere. Chemical gradients that could power microbial metabolism. The elements required for life as we know it — carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur — are all present on Mars.
If life emerged on Earth under conditions similar to or harder than ancient Mars offered — and the evidence suggests life emerged on Earth relatively quickly after the planet became habitable, as early as 3.5 billion years ago — there is no obvious reason it could not have emerged on Mars under comparable conditions.
The question is not whether the conditions were right. The conditions appear to have been right. The question is whether the emergence of life was a near-inevitable consequence of those conditions — a common outcome whenever suitable chemistry exists for long enough — or an extraordinarily unlikely event that happened once on Earth and perhaps nowhere else.
What Perseverance is looking for:
The rock samples Perseverance is collecting from Jezero Crater's ancient lake bed and river delta are chosen specifically for their biosignature preservation potential. If microbial life existed in ancient Mars's shallow lakes and rivers, the sedimentary rock formations of a fossil lake bed are exactly where we would expect to find chemical or morphological traces of it.
Biosignatures — evidence of past biology — can take multiple forms. Chemical signatures of organic molecules in specific patterns that biology creates but abiotic chemistry rarely does. Morphological signatures — shapes in rock that resemble microbial structures like stromatolites. Isotopic signatures — specific ratios of carbon, sulfur, or other isotope pairs that biological processes characteristically produce.
The reason Earth-laboratory analysis is required — rather than rover-based analysis — is that the most definitive biosignature tests require instruments too large and too technically complex to miniaturize for Mars deployment. The mass spectrometers, electron microscopes, and genomic sequencing tools that would definitively characterize biological signatures require laboratory facilities.
If the Mars Sample Return mission succeeds in bringing Perseverance's samples to Earth, these samples will be the most scientifically valuable objects ever delivered to an Earth laboratory — and their analysis could provide the most significant scientific discovery in human history if biological signatures are found.
The Question of Present Life — Underground and in the Clouds
Past life — if it existed — may not be the only life story Mars has to tell. Two specific environments on present-day Mars have generated genuine scientific interest as potentially supporting extant life — life existing today.
Subsurface liquid water:
The same process that produced subsurface liquid water on Jupiter's moon Europa and Saturn's moon Enceladus — where radioactive decay and tidal forces maintain liquid water beneath ice shells — may be operating on Mars. In 2018, the MARSIS radar instrument aboard the Mars Express orbiter detected radar reflections from beneath the south polar ice cap that are consistent with liquid water — possibly a subglacial lake approximately twenty kilometers wide, maintained in liquid state by the pressure of the overlying ice and the presence of dissolved salts that lower water's freezing point.
Subsequent analysis has both supported and questioned this interpretation — some researchers arguing the radar signatures are consistent with other explanations, others maintaining that liquid water is the most parsimonious interpretation of the data. The question remains genuinely scientifically contested.
If subglacial liquid water exists on Mars, it would represent a potential habitat for microbial life — isolated from the harsh surface radiation environment by kilometers of ice, potentially supplied with chemical energy from water-rock interactions, and thermally stable over geological timescales.
The Venusian clouds analogy:
More speculatively, some researchers have proposed that the Martian atmosphere — particularly the relatively sheltered mid-altitude cloud layers where temperature and pressure conditions are marginally less extreme than the surface — could potentially host airborne microbial life. The analogy is to the floating life hypothesis for Venus's clouds, where conditions in specific altitude bands are more Earth-like than Venus's brutal surface.
The Martian atmosphere is far too thin and too dry to be a convincing microbial habitat candidate by most current scientific assessment. But the proposal represents the kind of creative consideration of non-obvious habitats that the history of extremophile discovery on Earth — where life has been found in environments previously considered definitively uninhabitable — suggests should not be immediately dismissed.
Human Life on Mars — The Engineering Reality
Moving from the question of whether Mars has or had indigenous life to whether human life could exist there involves an entirely different set of challenges — the engineering and biological challenges of sustaining a human organism in an environment that is comprehensively hostile to human life as it evolved.
The atmosphere problem:
Mars's atmosphere is approximately ninety-five percent carbon dioxide, three percent nitrogen, and two percent argon — with trace amounts of oxygen and other gases. The total atmospheric pressure is approximately six hundred Pascals — less than one percent of Earth's sea level pressure of approximately one hundred thousand Pascals.
Humans require atmospheric oxygen at sufficient partial pressure to oxygenate the blood. Mars's atmosphere provides neither sufficient oxygen nor sufficient pressure to sustain human respiration even if the oxygen composition were appropriate. Any human presence on Mars requires either living within pressurized habitats or wearing pressure suits at all times outside — there is no middle ground.
The good news: NASA's MOXIE experiment aboard Perseverance has successfully demonstrated the production of oxygen from Martian carbon dioxide through electrolysis — proving the technical feasibility of producing breathable oxygen from Martian atmospheric resources. This technology demonstration is an important step toward in-situ resource utilization — using Mars's local resources rather than transporting everything from Earth.
The radiation problem:
Mars lacks both Earth's magnetic field and Earth's thick atmosphere — both of which protect Earth's surface from cosmic radiation and solar particle events. Mars's surface receives radiation doses approximately forty to fifty times higher than Earth's surface — at levels that would significantly increase cancer risk for humans living there over extended periods.
Underground habitats — burrowed into Mars's regolith or built beneath meters of shielding material — provide the most practical radiation protection. Mars's regolith itself could serve as shielding material if sufficient depth is maintained above habitats. But the surface radiation environment makes unprotected surface activity genuinely dangerous over extended timescales.
The temperature problem:
Mars's average surface temperature of negative sixty degrees Celsius — with extremes far colder — requires heated habitats and insulated pressure suits. The temperature management challenge is manageable from an engineering perspective — the technology for maintaining heated enclosed environments in extreme cold exists and has been demonstrated in Antarctic research stations and space habitats. But it adds to the cumulative engineering complexity of sustained Mars presence.
The water problem:
Water is essential for human survival — for drinking, for hygiene, for growing food, and for producing rocket propellant from hydrogen and oxygen components. Mars has water — but in forms that require significant effort to access.
The Martian polar ice caps contain significant water ice alongside carbon dioxide ice. Subsurface ice deposits have been identified at multiple locations across Mars through orbital radar observations. The regolith contains chemically bound water in hydrated minerals.
Accessing this water — extracting it, purifying it, and managing it within a closed-loop system that maximizes recycling — is technically challenging but not physically impossible. The ISS provides a proof of concept for closed-loop water recycling in space environments, recovering approximately ninety-three to ninety-five percent of all water from multiple sources including urine and atmospheric moisture.
The food problem:
Sustained human presence on Mars cannot be supplied by food shipments from Earth — the transit time of six to nine months and the cost of mass transport from Earth make indefinite food supply from Earth impractical at any meaningful settlement scale.
Food production on Mars requires either growing food in enclosed controlled agricultural facilities using Mars's resources, or developing food from in-situ chemical resources through processes that do not require soil or conventional agriculture.
Controlled agricultural facilities using artificial lighting, hydroponic growing systems, and recycled nutrients from biological waste could theoretically produce sufficient calories for a small Mars population. Research on space agriculture has been ongoing on the ISS, and the plant growth experiments conducted there provide genuine data about food production in space environments.
The specific challenges of Mars agriculture include providing sufficient artificial lighting energy at Mars's greater distance from the Sun, maintaining appropriate atmospheric composition in growing facilities, managing plant biology in Mars's one-third Earth gravity environment, and preventing contamination between biological systems and the Martian environment.
The Gravity Problem — The Least Discussed Challenge
Mars's surface gravity is approximately thirty-eight percent of Earth's — meaning a person who weighs seventy kilograms on Earth would weigh approximately twenty-seven kilograms on Mars. This seems like a minor detail compared to the atmosphere and radiation challenges. It is actually one of the most significant long-term challenges for human Mars settlement.
What reduced gravity does to human physiology:
Earth's life — including human life — evolved in one gravity. Our skeletons, our cardiovascular systems, our vestibular systems, our fluid distribution, and our immune function are all calibrated for one gravity. The ISS has provided extensive data on what microgravity — zero gravity — does to human physiology over extended periods: bone density loss, muscle atrophy, cardiovascular deconditioning, vision problems from fluid redistribution toward the head, and immune system changes.
Thirty-eight percent gravity is better than zero gravity — but whether it is sufficient to maintain human health over years and decades is genuinely unknown. No human has ever experienced sustained reduced gravity — the ISS provides microgravity data but not partial gravity data. We do not know, from direct evidence, whether the human body can maintain adequate health in Mars gravity over the multi-year timescales that settlement would require.
The implications extend to reproduction — whether human conception, gestation, and infant development are viable in Mars's gravity is a question with profound implications for any permanent settlement but one that cannot be answered without actually being on Mars for extended periods.
This is perhaps the most significant genuinely unknown variable in the human Mars settlement question — not because it is necessarily insurmountable but because we do not yet have data to assess whether it is a manageable challenge or a fundamental barrier.
The Terraforming Question — Could Mars Be Made Earthlike?
Terraforming — the hypothetical process of transforming Mars's environment to make it more Earth-like over very long timescales — has been discussed as a long-term solution to Mars's hostile conditions.
The concept is scientifically serious even if currently beyond practical capability. In principle, releasing the carbon dioxide trapped in Mars's polar ice caps and regolith could thicken the atmosphere and raise temperatures through a greenhouse effect. Introducing nitrogen from available sources could build an atmosphere with a composition closer to Earth's. Over millennia, if photosynthetic organisms were established and flourished, atmospheric oxygen could gradually build to breathable levels.
The honest assessment of terraforming:
The timescales involved are genuinely enormous — the minimum realistic timescale for meaningful terraforming progress is centuries, with full Earth-like conditions potentially requiring millennia. The energy and resource requirements are beyond any currently foreseeable technology. Mars's lack of a magnetic field — which no currently envisioned technology can recreate at planetary scale — means any terraformed atmosphere would continue to be gradually stripped by the solar wind over geological time, making terraforming at best a temporary rather than permanent solution without a magnetic field solution.
Terraforming is probably not the near-term Mars question. The near-term Mars question is whether small, enclosed human settlements with life support technology can establish sustained human presence. Terraforming, if it is ever attempted, is the work of civilizations centuries hence rather than the mission planning of the coming decades.
The Planetary Protection Question — The Ethics Nobody Discusses Enough
Here is the dimension of the life-on-Mars question that generates the least public discussion and deserves significantly more.
If Mars has indigenous microbial life — either surviving in subsurface habitats or preserved in ancient sediments — what are our ethical obligations regarding that life?
Human presence on Mars involves bringing enormous quantities of Earth biology — human microbiomes, the microbiomes of food plants, inadvertent contamination of equipment with Earth organisms that may survive in protected niches on Mars. The contamination risk is not theoretical. Certain Earth extremophiles — organisms that survive in extremely hostile conditions — might potentially survive in specific Martian environments.
If Earth organisms contaminate Mars and establish themselves before we determine whether Mars has indigenous life, we lose the ability to ever determine whether life found on Mars originated there or was introduced by us. This would be one of the greatest scientific losses in human history — the permanent forfeiture of knowing whether life arose independently on Mars, one of the most significant questions in all of science.
Planetary protection protocols — the procedures governing sterilization of Mars-bound hardware and the restrictions on where landers and rovers are permitted to operate — represent the scientific community's attempt to manage this risk. But the standards applicable to robotic missions may not be achievable for human missions — humans are inherently biological, and the quantities of Earth organisms they would bring to Mars are vastly larger than any robotic contamination.
The tension between human Mars exploration and Mars planetary protection is genuinely unresolved — and the scientific community's debate about how to manage it is one that deserves public engagement alongside the more exciting discussion of when and how humans will reach Mars.
What the Next Decade Actually Holds
Here is the honest near-term picture — the specific developments that are realistically expected in the coming decade that will advance our understanding of Mars and move human presence from aspiration toward possibility.
Mars Sample Return:
The joint NASA-ESA Mars Sample Return mission — if it proceeds on its planned timeline and within its budget — would bring Perseverance's cached samples to Earth laboratories in the early 2030s. The analysis of these samples would be the single most significant near-term development in the life-on-Mars question — potentially providing definitive evidence of ancient life or definitively ruling it out in the specific geological contexts Perseverance has sampled.
Artemis and the Moon as Mars preparation:
NASA's Artemis program — establishing sustained human presence on the Moon — is explicitly framed as preparation for Mars missions. The technologies, the operational experience, and the biological data gathered from extended human lunar presence directly inform Mars mission planning. How humans manage radiation exposure, how closed-loop life support systems perform over multi-month missions, how human physiology responds to partial gravity in the lunar environment — all of this Mars-relevant data will be gathered through lunar operations before the first human Mars mission.
SpaceX Starship development:
SpaceX's Starship program — which Elon Musk has explicitly designed for Mars missions — is the current most realistic near-term candidate vehicle for human Mars transportation. Its development trajectory, its demonstrated capabilities, and its economic model are genuinely relevant to the question of when human Mars presence becomes practically achievable.
ISRO's Mars missions:
India's Mangalyaan Mars Orbiter Mission demonstrated ISRO's capability to reach Mars successfully on its first attempt — one of only four space agencies to achieve this. Future Indian Mars missions will contribute to the global scientific characterization of Mars that informs both the life search and the human settlement question.
The Honest Answer — Is Life on Mars Really Possible?
Let me give you the specific, honest answers to both versions of this question.
Was there life on Mars in the past?
Unknown — but genuinely scientifically plausible. The conditions of ancient Mars were by available evidence compatible with microbial life as we understand it. Whether life actually emerged under those conditions depends on questions about the origin of life that we cannot yet answer definitively even for Earth. The Mars Sample Return mission may provide the most direct evidence available for addressing this question. Current scientific assessment places the possibility as genuine and worth investigating seriously rather than as remote speculation.
Is there life on Mars today?
Unlikely on the surface — the surface radiation environment, extreme cold, and absence of liquid water make the current Martian surface hostile beyond what any known Earth organism could survive unprotected. More plausibly possible in specific subsurface or protected environments — subglacial liquid water if it exists, deep subsurface environments where liquid water might persist with geothermal heat, and deeply buried sediments where ancient organisms might be preserved in dormancy. Current scientific assessment considers present Martian life unlikely but not definitively ruled out, particularly in subsurface environments we have not yet directly accessed.
Can humans live on Mars?
Yes — technically, with sufficient engineering, resources, and technology. No physical law prevents humans from surviving on Mars within enclosed, engineered habitats. The challenges are engineering and economic rather than fundamental physical barriers. The timeline for when humans could establish sustained Mars presence ranges from optimistic estimates of the 2030s to more conservative estimates of the 2040s or 2050s.
Can humans permanently settle Mars?
Possibly — but with genuinely significant unknowns remaining, particularly regarding human reproductive biology in Mars gravity, the long-term sustainability of closed-loop life support systems, the economic viability of sustained supply chains from Earth, and the ethical implications of potential contamination of any indigenous Martian biosphere.
The honest answer to the title question is: life on Mars — past indigenous life, present indigenous life in protected environments, and future human life in engineered habitats — is genuinely scientifically possible. Whether it actually exists or has existed awaits evidence that current and near-future missions may provide.
Final Thoughts — The Question That Makes Us Human
Here is what I want to leave you with.
The question of whether there is life on Mars — whether we are or have been alone in the solar system — is not merely a scientific question. It is a philosophical one that touches something fundamental about how we understand our own existence and our place in the universe.
If we discover that life emerged independently on Mars — that the chemistry of life, given sufficient time and appropriate conditions, arises not once but at least twice in a single solar system — the implication is that life is probably a common feature of the universe. That the cosmos is likely teeming with it. That our loneliness is an illusion produced by the current limits of our instruments.
If we discover definitively that Mars never hosted life despite having conditions that seem adequate — that life did not emerge on Mars even when it had liquid water and chemistry comparable to early Earth — the implication is that the emergence of life may be an extraordinarily rare event. That what happened on Earth was perhaps uniquely fortunate. That the universe may be largely empty of life despite its billions of galaxies and trillions of stars.
Either answer is extraordinary. Either answer changes how we understand ourselves.
That is why Perseverance is driving across Jezero Crater right now collecting samples from ancient lake beds. Not for engineering demonstration. Not for national prestige. For the specific, ancient, profound human need to know whether we are alone.
We are closer to that answer than any previous human generation has ever been.
And what we find will be one of the most important things humanity has ever learned.
Frequently Asked Questions (FAQs)
Q1. Has any evidence of life on Mars ever been found?
No confirmed evidence of life on Mars has been found. The most discussed historical claim — the 1996 announcement by NASA scientists that the meteorite ALH84001, which originated from Mars, contained possible microfossils — was subsequently heavily contested and is not accepted as confirmed evidence of Mars life by the scientific community. Current missions including Perseverance are specifically designed to search for biosignatures in ancient Martian rock formations, and the Mars Sample Return mission would bring these samples to Earth laboratories for definitive analysis. No current evidence confirms life on Mars — but the search is being conducted with unprecedented scientific rigor and technological capability.
Q2. How long would it take to travel to Mars?
The minimum energy trajectory from Earth to Mars — called a Hohmann transfer orbit — takes approximately six to nine months depending on the specific orbital positions of Earth and Mars at launch. Mars and Earth align for efficient travel approximately every twenty-six months — these are called launch windows. The journey duration creates significant challenges for human missions including radiation exposure during transit, physiological deconditioning in microgravity, and the psychological demands of prolonged confinement. SpaceX's Starship, using higher-energy trajectories made possible by its large propellant capacity, might reduce transit time to approximately three to four months according to current planning.
Q3. What would humans eat on Mars?
Sustained human presence on Mars requires food production on Mars rather than continuous resupply from Earth. The most developed concept is enclosed controlled agricultural facilities using hydroponic or aeroponic growing systems with artificial lighting, recycled nutrients, and carefully controlled atmospheric composition. Research on space agriculture — including plant growth experiments on the ISS — has demonstrated the feasibility of growing food in space environments. Candidate crops for Mars agriculture include potatoes, sweet potatoes, lettuce, soybeans, and other plants that produce high caloric or nutritional density relative to growing space and resource requirements. A complete Mars diet would likely combine grown plant foods with cultured protein sources and carefully managed nutritional supplementation.
Q4. Why does Mars not have a magnetic field and can one be created?
Mars lost its global magnetic field approximately four billion years ago as its smaller iron core cooled and its internal convection — which drives the dynamo effect that generates planetary magnetic fields — ceased. The core is now largely solid and no longer generates significant magnetic field. Creating an artificial planetary magnetic field is discussed in some theoretical frameworks — including a proposal to deploy a magnetic dipole shield at the Mars-Sun L1 Lagrange point that would deflect solar wind before it reaches Mars — but no such technology is currently developed or demonstrably feasible at the required scale. The absence of a magnetic field remains one of the most fundamental long-term challenges for both the atmospheric retention of any terraforming effort and the radiation protection of human inhabitants.
Q5. How is India involved in Mars exploration?
India's Mangalyaan Mars Orbiter Mission — launched in 2013 and reaching Mars orbit in 2014 on its first attempt — made ISRO only the fourth space agency to successfully reach Mars, and the first Asian agency to do so. Mangalyaan studied Mars's surface features, morphology, mineralogy, and atmosphere from orbit. India signed the Artemis Accords — the framework for international lunar and deep space exploration cooperation — positioning ISRO as a partner in the broader international effort toward deep space exploration including eventual Mars missions. India's growing space capabilities and its demonstrated Mars orbital insertion success on a first attempt establish ISRO as a credible potential contributor to future Mars exploration missions, either independently or through international collaboration.
Q6. What is planetary protection and why does it matter for Mars?
Planetary protection refers to the protocols and practices designed to prevent Earth organisms from contaminating Mars — forward contamination — and to prevent potential Mars organisms from contaminating Earth — backward contamination. Forward contamination matters because Earth extremophiles might potentially survive in specific Martian environments, and if they established themselves before we determined whether Mars has indigenous life, we would permanently lose the ability to distinguish Earth-introduced life from indigenous Martian life. All Mars-bound hardware is sterilized to specific planetary protection standards, and certain areas of Mars — regions considered potentially habitable — are designated as special regions where landing is restricted to the most rigorously sterilized spacecraft. The challenge for human missions is that humans carry vast quantities of Earth biology that cannot be sterilized away, making human planetary protection management significantly more complex than robotic mission planetary protection.