# Six men spent 520 days inside the Mars500 chamber and by the later stages of the mock trip to Mars they were judging unpleasant pictures less harshly while mood scores and stress-linked hormones shifted in patterns that resembled the mission’s psychologically difficult third quarter

> 520 days is long enough for a simulated Mars trip to stop feeling like a technical rehearsal and start exposing how people adapt under pressure. In one of the clearest psychological signals from the Mars500 isolation study, six crew members gradually gave...

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Published: 2026-08-11T01:45:08+00:00
Categories: Explainer, Space

![Astronaut in spacesuit explores barren, Mars-like desert terrain under brown sky](https://www.argo.net/wp-content/uploads/2026/08/Mars500_habitat_1200x675.jpg)

520 days is long enough for a simulated Mars trip to stop feeling like a technical rehearsal and start exposing how people adapt under pressure. In one of the clearest psychological signals from the **Mars500** isolation study, six crew members gradually gave more positive ratings to unpleasant images as the mission moved deeper into confinement.

Researchers reported that pattern in a [PLoS One study](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0087087) that tracked emotional ratings, mood questionnaires and blood markers during the sealed mission. The crew did not simply become cheerful over time. Their responses changed in a more uneven way, with late-mission shifts in the way negative images were judged and with parallel changes in several hormones linked to stress and regulation.

The result matters because real crews bound for deep space will spend months in a small habitat with delays in communication, repeated routines and no immediate return home. [ESA's overview of Mars500](https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Mars500/Mars500_study_overview) describes the project as a way to study exactly those long-duration pressures before astronauts face them on an actual interplanetary mission. [NASA identifies isolation and confinement](https://www.nasa.gov/hrp/hazard-isolation-and-confinement/) as one of the major hazards crews will face beyond Earth.

## Mars500 was designed to mimic a long trip to Mars

The **Mars500 simulator** ran from June 2010 to November 2011 at the **Institute of Biomedical Problems** in Moscow. Six men, three Russian, two European and one Chinese, lived inside a spacecraft-like complex that imposed isolation, a mission schedule, delayed communication and a simulated Mars landing phase. The setup removed launch danger and weightlessness, but it kept many of the social and psychological demands that a real crew would face.

Mission planners have long treated confinement as more than a comfort issue. The crew had to keep up work, handle routines, monitor systems and manage their own physical and psychological state while cut off from ordinary social life. The **European Space Agency** notes that the study was meant to support countermeasures, crew selection and mission design for future exploration beyond low Earth orbit.

That is why the paper did more than ask whether the men felt stressed. The team wanted to see whether prolonged isolation would alter the way the crew processed emotional material, whether mood would rise and fall in stages and whether those changes would travel alongside measurable biochemical shifts rather than appearing only in self-reports.

## The crew began rating unpleasant pictures more positively

To test emotional processing, the researchers used the **International Affective Picture System**, a standardized image set widely used in psychology. Across eight test sessions, the men rated pleasant, neutral and unpleasant pictures for valence and arousal. The most striking effect appeared in the ratings for new unpleasant images. As the mission progressed, the gap between pleasant and unpleasant ratings narrowed, especially around the later parts of confinement.

In plain terms, the unpleasant images looked a little less negative to the crew than they had earlier in the mission. The study did not find the same drift for pleasant or neutral pictures and arousal ratings remained comparatively stable. That pattern suggests a specific change in how negative material was being judged rather than a blanket flattening of every emotional response.

The authors also checked whether one unusual participant was driving the effect. Their individual plots showed that the tendency appeared in nearly every crewmember. That made the signal more useful for mission research, because it looked like a group-level adaptation rather than one person's eccentric scoring habit.

## Mood scores and hormones shifted in stages

The picture ratings did not stand alone. The crew also completed the **Profile of Mood States** questionnaire, which tracks dimensions such as tension, depression, fatigue, confusion and vigor. The strongest statistical change over time appeared in vigor-activity and the broader mood disturbance pattern moved in a stage-like way even when every comparison did not reach significance.

Blood samples added a second layer. The team measured **cortisol**, serotonin, dopamine and norepinephrine from plasma collected in the morning before breakfast. Norepinephrine and serotonin rose markedly in the middle stretch of the mission, close to the simulated Mars landing period, while cortisol fluctuated and reached its highest value near the end. Dopamine showed a weaker decline before leveling out.

Those biological changes did not prove a single cause, but they were not random decoration around the main result. The paper found correlations linking the image ratings with mood scores and with shifts in norepinephrine and serotonin. The combined picture suggests that long confinement was altering both subjective state and parts of the crew's regulatory chemistry.

## The late-mission pattern resembled the third-quarter problem

Researchers who study polar expeditions, submarines and other isolated environments have long discussed the **third-quarter phenomenon**. The idea is that the hardest part of a long mission often arrives after the midpoint, when the novelty is gone, the finish is still distant and the remaining duration feels heavy in a new way. The Mars500 team argued that their stage-like findings looked broadly similar to that pattern.

The paper did not claim that every classic symptom appeared in a textbook form. Instead, it showed a late-mission clustering of changes: vigor moved, unpleasant images were rated more positively and hormone measures shifted around the same broad period. Readers can also compare the formal abstract in the [PubMed record](https://pubmed.ncbi.nlm.nih.gov/24695321/), which summarizes the same conclusion in a more compact biomedical style.

What might explain the change? The authors proposed a kind of defensive adjustment. If negative material keeps pressing on an already taxed crew, the mind may soften its evaluation to reduce further strain. That does not mean the crew was misreading reality in every context. It means prolonged confinement may encourage a protective bias when people confront new unpleasant stimuli again and again.

## Why this old simulation still matters for future crews

The Mars500 paper remains relevant because future exploration plans still face the same human problem: a crew can be technically healthy and still accumulate psychological wear over months of confinement. Habitat design, schedules, privacy, communication planning and onboard mental health support all depend on understanding when those pressures intensify and how they show up before performance begins to slip.

[NASA's behavioral health risk summary](https://www.nasa.gov/reference/risk-of-behavioral-changes-and-psychiatric-disorders/) explains why mission planners track psychological performance alongside physical health. The Mars500 study also has limits. It involved only six men in a ground simulation, with no microgravity and no real launch or landing danger, so it cannot be treated as a complete forecast for a Mars crew. Even so, it offers a rare long-duration dataset with emotional, behavioral and biochemical measures collected in the same mission.

It also highlights how easily a mission team could miss a meaningful psychological shift if it watched only one channel. A crew might still complete scheduled work, answer routine questions and avoid open conflict while their interpretation of negative signals quietly changes. For flight surgeons and behavioral support teams, that argues for layered monitoring that combines performance checks, mood measures, biological data when practical and careful attention to phase changes around the middle and late portions of a mission. Single dashboards rarely capture that full pattern on their own.

The practical lesson is straightforward. A deep-space crew may continue working and cooperating while their internal handling of negative information gradually changes. That is the kind of subtle shift mission teams need to detect early and reliably. Countermeasures for future exploration will probably have to support sleep, workload balance, social climate and emotional regulation at the same time, because Mars-class isolation affects all of them together rather than one at a time.