The Origins of the Blob ISS Experiment
The idea of sending slime mold to space came from Audrey Dussutour, a CNRS (Centre National de la Recherche Scientifique) researcher at the University of Toulouse who has spent years studying Physarum polycephalum. Dussutour, who had already published extensively on slime mold behavior including memory, learning, and decision-making, proposed an experiment to test how the organism would behave in microgravity.
The project was developed in partnership with CNES (Centre National d'Etudes Spatiales, the French space agency) and the CADMOS center, which manages French experiments aboard the ISS. French astronaut Thomas Pesquet, who was stationed on the ISS during the Alpha mission (April to November 2021), carried out the experiment in orbit.
Scientific Questions
The experiment sought to answer several questions about how slime mold behaves when removed from Earth's gravity:
- Movement and exploration: does Physarum explore space differently in microgravity? On Earth, the organism uses gravity as one of its environmental cues. Without it, would it grow differently?
- Network formation: would the vein network be structured differently without the directional influence of gravity?
- Cytoplasmic streaming: the rhythmic flow that drives slime mold movement depends partly on pressure gradients. Would microgravity disrupt these patterns?
- Dormancy recovery: the samples were sent as dried sclerotia (dormant form). Would they revive normally in space conditions?
These questions have broader relevance for understanding how single-celled organisms adapt to space, which matters for long-duration space missions where biological systems (for life support, food production, or waste recycling) will need to function in microgravity.
Methodology
Preparing the samples
The team at CNRS prepared the slime mold samples months before launch. Physarum polycephalum was grown in the laboratory, then induced to enter sclerotium (dormant) state by gradually drying the cultures. Sclerotia are extremely resilient: they can survive for months or even years without food or water, and they revive when rehydrated.
The dried sclerotia were placed on filter paper inside sealed Petri dishes. Multiple samples were prepared to allow for replication and different experimental conditions.
The experimental setup
Two parallel experiments were conducted:
| Parameter | ISS Experiment (Space) | Ground Control (Earth) |
|---|---|---|
| Location | International Space Station, Columbus module | CADMOS center, CNES, Toulouse |
| Gravity | Microgravity (~0 g) | Normal gravity (1 g) |
| Temperature | Controlled, matching ground | Controlled, matching ISS |
| Lighting | Standardized | Standardized |
| Humidity | Rehydration protocol | Identical rehydration protocol |
| Food sources | Condition A: no food; Condition B: multiple oat flakes | Same conditions |
| Observation | Time-lapse photography | Time-lapse photography |
Thomas Pesquet rehydrated the sclerotia to wake them from dormancy, then monitored them over several days using cameras that captured images at regular intervals. The exact same protocol was followed simultaneously on Earth in Toulouse, so that any differences in behavior could be attributed to microgravity rather than other variables.
Two experimental conditions
Each location (space and ground) ran two conditions:
- Exploration without food: the slime mold was rehydrated with no food source present, to observe pure exploration behavior
- Exploration with food: multiple oat flakes were placed in the dish, to observe network formation between food sources
This design allowed researchers to separate the effects of microgravity on basic movement from its effects on network optimization.
Results and Observations
Successful revival
The slime mold sclerotia revived successfully in space. This confirmed that Physarum polycephalum can recover from dormancy in microgravity, an important finding for any future use of biological systems in space. The revival process on the ISS took slightly longer than on Earth, but the organisms were fully functional.
Altered exploration patterns
The most notable result was that slime mold in microgravity explored in three dimensions. On Earth, Physarum is essentially confined to two-dimensional growth along surfaces because gravity pins it down. In space, the plasmodium was observed growing upward from the substrate, forming pillars and bridges in the air above the agar surface.
This three-dimensional growth had never been observed before and suggested that gravity normally constrains slime mold architecture more than previously realized.
Network differences
When food sources were present, the slime mold in space still formed networks connecting them, but the network structure showed some differences compared to the ground control:
- Veins in space were thicker on average
- The network showed more vertical branching
- Connection times between food sources were slightly slower
Thomas Pesquet's observations
Pesquet, who documented the experiment through videos shared with the public, described watching the Blob wake up and begin to explore as one of the highlights of his mission. His enthusiasm helped generate significant media coverage and public interest in the project.
The Educational Program: "Elevez votre Blob"
Perhaps the most remarkable aspect of the Blob ISS experiment was its educational component. CNRS and CNES organized a parallel experiment called "Elevez votre Blob" (Raise Your Blob) in which approximately 350,000 students across 4,500 schools in France conducted the same experiment at their desks.
How it worked
- Distribution: CNRS sent dried sclerotia kits to participating schools, along with detailed protocols
- Simultaneous experiment: students rehydrated their blobs at the same time as Thomas Pesquet did on the ISS
- Observation: students photographed and documented their blob's behavior over several days
- Comparison: classes compared their results (Earth, normal gravity) with the ISS results (microgravity), which were shared through the CNES educational platform
- Data submission: schools submitted their observations, creating a large citizen science dataset
Educational impact
The program was one of the largest participatory science experiments ever conducted in France. It introduced students from elementary through high school to:
- The scientific method (hypothesis, controlled experiment, observation, analysis)
- Biology of single-celled organisms
- Space science and the ISS
- Data collection and comparison
- The concept of a control experiment
Many teachers reported that the Blob experiment was uniquely effective at engaging students because the organism is visually fascinating, easy to care for, and behaves in unexpected ways. Students could see their blob growing, moving, and making "decisions" in real time.
Media Coverage and Public Response
The Blob ISS experiment received extensive coverage in French and international media. Several factors contributed to its popularity:
- Thomas Pesquet's popularity: Pesquet is one of the most recognizable astronauts in Europe, with millions of social media followers
- The organism's charisma: a bright yellow blob growing in space is inherently photogenic and shareable
- Audrey Dussutour's communication skills: Dussutour is an effective science communicator who has given TED talks and written popular books about slime mold
- The student angle: 350,000 children doing the same experiment as an astronaut made for compelling stories
The experiment significantly raised public awareness of slime molds in France and beyond, contributing to the ongoing "blob mania" that has made Physarum polycephalum a cultural phenomenon.
Scientific Significance
Beyond the immediate results, the Blob ISS experiment matters for several reasons:
Understanding biological adaptation to space
Most space biology research focuses on plants, bacteria, or human cells. Studying a large, single-celled eukaryote like Physarum fills a gap in our understanding of how different types of organisms respond to microgravity. The fact that the slime mold grew in three dimensions in space raises questions about whether other amoeboid organisms would behave similarly.
Implications for space life support
Future long-duration space missions (to Mars and beyond) will likely rely on biological systems for air recycling, waste processing, and food production. Understanding how organisms like slime molds function in space contributes to the broader knowledge base needed to design these systems.
Cytoplasmic streaming without gravity
The observation that cytoplasmic streaming continued in microgravity, though with altered patterns, provides data for biophysicists studying the mechanics of intracellular flow. On Earth, gravity contributes to the pressure gradients that drive streaming. The space experiment showed that other forces (osmotic pressure, actin-myosin contractions) are sufficient to maintain flow even without gravitational assistance.
Previous Slime Mold Space Research
The 2021 ISS experiment was not the first time slime mold went to space. Earlier studies include:
- 1985 Spacelab mission: a German experiment studied Physarum cytoplasmic streaming in microgravity aboard the Space Shuttle, finding that the basic rhythm of streaming was maintained
- Various parabolic flight experiments: short-duration microgravity exposures (during parabolic airplane flights) had previously shown that Physarum responds to changes in gravity within seconds
However, the 2021 experiment was by far the most comprehensive, with longer observation periods, controlled conditions, and the massive parallel ground experiment.
What Comes Next?
The success of the Blob ISS experiment has opened doors for further research:
- Extended duration studies: future experiments could observe slime mold over weeks or months in space, allowing researchers to study long-term adaptation
- Different species: testing other myxomycete species (see our species guide) in microgravity could reveal how universal or species-specific the 3D growth response is
- Radiation effects: space exposes organisms to higher radiation levels. Future studies could examine how cosmic radiation affects slime mold behavior and DNA
- Moon and Mars gravity: testing at 1/6 g (Moon) or 1/3 g (Mars) would show how much gravity is needed to constrain slime mold to 2D growth
Audrey Dussutour and her team continue to analyze data from the 2021 experiment and are developing proposals for follow-up studies.
How to Learn More
If the space experiment sparked your interest in slime mold, here are some next steps:
- Read about what slime mold is for a general introduction
- Learn how to grow your own slime mold at home
- Explore the experiments you can do with a home culture
- Understand the science of dormancy and sclerotium, the state in which the blob traveled to space
- Discover the broader scientific applications of slime mold research
The Blob ISS experiment stands as a remarkable example of how a humble single-celled organism can bridge the gap between cutting-edge space research and hands-on classroom science. It demonstrated that Physarum polycephalum is not just a laboratory model organism but an explorer capable of adapting to one of the most extreme environments imaginable.