Why send a slime mold to space?
On Earth, a slime mold never escapes gravity. Water runs downhill through its substrate, its cytoplasm sloshes back and forth in a world with a fixed "down," and every vein in its network is built under that constant pull. Nobody can say how much gravity shapes the way it explores, because there has never been a version of the organism that grew without it.
Weightlessness removes that variable. The question behind the experiment was simple: without an up or a down, does Physarum polycephalum still spread, build its network and find food the same way?
How the experiment worked
The experiment flew during Alpha, the mission of French astronaut Thomas Pesquet, who launched in April 2021 and returned in November 2021. It was designed by CNES, the French space agency, with Audrey Dussutour, a CNRS researcher in Toulouse.
Four slime molds in a closed box
Four pieces of strain LU352, chosen because it is hardy, reached the ISS on 12 August 2021 as dry sclerotia. They travelled in an opaque, sealed "blob box" built by CNES and split into four compartments. Two of them had four oat flakes laid out in a square. The other two had no food at all.
Wake-up call on 2 September 2021
Thomas Pesquet injected 0.3 ml of water into each compartment with a syringe, without ever opening the box, then fixed it to a wall of the Columbus module. A built-in camera took one picture every ten minutes, with a brief flash of light so as not to disturb an organism that avoids light.
A second run after a glitch
A recording fault lost about half the images from the first run, which ended on 9 September. With the go-ahead from NASA and ESA, the experiment was restarted on 13 September for five more days, this time with a backup memory card.
What the experiment actually showed
The first result is the simplest one. All four sclerotia woke up in orbit, and the slime molds grew inside their box. Beyond that, honesty calls for caution. The project was educational from the start, and Audrey Dussutour said before the flight that no scientific paper would come out of it, because four slime molds are far too few to draw solid conclusions.
The photos taken on board were used as a reference point by schools, which were watching their own slime molds at the same time. Because part of the images were lost in the glitch, any comparison between orbit and the ground remains qualitative. You may read elsewhere that the slime mold grew in three dimensions in space, or built thicker veins. No published data supports those claims.
The school program that ran alongside
CNES, together with CNRS and the Toulouse education authority, offered the experiment to 4,500 schools, from primary level to high school. Kits were shipped at the end of August 2021, and classes ran the ground version in October, in two sessions timed to match the two runs on the ISS.
Each class received sclerotia and a protocol close to the one used in flight, with fed and unfed slime molds. Pupils could then compare their own observations with the pictures taken by the station's camera, which were shared with teachers from 11 October onward. In France the operation was called Élève ton blob, "raise your blob."
Try the ground version yourself
Set up two dishes with the same damp substrate and a piece of slime mold in the middle of each. Put four oat flakes in a square in the first dish and nothing in the second, then photograph both at regular intervals. The difference between a fed and a hungry slime mold is striking on its own. Our guide to experiments at home has more ideas.
Why the slime mold was the right passenger
Flying anything to orbit is expensive and comes with strict rules. The payload has to be light, run without power, need no more than a few simple gestures from the crew, and tolerate a long wait on the ground before launch.
The slime mold ticks every box thanks to its sclerotium. Dry, light and stable at room temperature, it travels without fuss and comes back to life with a few drops of water. Very few organisms offer that combination, and it is this property, more than its fame, that made the experiment possible.
The ground experiment was the real novelty
What made the operation unusual was not the flight itself but its mirror on the ground. Thousands of French classes received sclerotia and a protocol copied from the flight, and ran the experiment at the same time as the astronaut.
Four slime molds in weightlessness were set against a very large number of control slime molds on Earth, which is rare in space biology. For a teacher, the protocol is still fully reproducible today, as described in our page on slime mold in the classroom.
Frequently asked questions
When did slime mold go to space?
In 2021, during Thomas Pesquet's Alpha mission aboard the International Space Station, in an experiment designed by CNES with CNRS.
In what form did the slime mold travel?
As dry sclerotia, its dormant form. Thomas Pesquet rehydrated them in orbit on 2 September 2021 by injecting 0.3 ml of water into each compartment of their box.
Did the slime mold survive weightlessness?
Yes. The sclerotia revived and the slime molds grew in orbit. That was the main result, since the experiment was too small to support firmer conclusions.
Can a class repeat the experiment?
Yes. All you need are sclerotia, clear dishes and oat flakes. It is one of the few space protocols that can be run in full in an ordinary classroom.
Sources
- CNES, Élève ton blob teacher resources, Alpha mission (2021), in French.
- CNES, Le réveil a sonné pour les blobs à bord de l'ISS (2021), in French.
- Société astronomique de France, L'expérience éducative Élève ton blob (15 October 2021), in French.
- Astrobiology, Physarum polycephalum heads for space (19 April 2021).