There are mice on ISS. Not the first non-human mammals and likely not the last. Their health provides insights on influence of microgravity on organisms.

Very few humans stayed in space for longer than a year; after that period the health impact becomes too serious to allow them remain. What about mice, or other animals though? Have any stayed longer? And if so, what were the effects?

...I'm asking this in relation to the recent How much gravity is actually needed to avoid serious health consequences?. Building a centrifugal human habitat and letting the crew remain there well in excess of one year is impractical due to the cost. But building a centrifuge for some small animals? With mouse lifespan being only around two years, that wouldn't be too indicative, but guinea pigs reach age of 10, which should provide a plenty of data on influence of various levels of gravity on health.

  • $\begingroup$ Whales live in a weightless environment, and are long-lived mammals. I know it's not what you are asking! $\endgroup$
    – Juancho
    Jul 2, 2016 at 2:14
  • 3
    $\begingroup$ Whales do not live in a weightless environment; their weight is supported by water as our bodies are supported by the ground; their ventral organs are compressed by the weight of their dorsal parts and the water column above them, etc. $\endgroup$ Jul 2, 2016 at 2:19
  • $\begingroup$ @RussellBorogove: In case of a whale (diameter 4.5m) that's about 0.43 bar difference between top and bottom of the animal, its own mass providing the rest of the difference (and creating the "exercising stress"). But with smaller aquatic animals, the difference is negligible, pressure "from below" roughly equal to pressure "from above", so gravity plays no significant role in their development. But then, water viscosity more than makes up for that. $\endgroup$
    – SF.
    Jul 4, 2016 at 7:43
  • $\begingroup$ @SF. Yeah, but their body is "at rest" relative to everything else, and their internal organs are being attracted to the Earth, and being supported by their skeletal structure/skin. Those organs "feel gravity", just like the fish itself does. A skydiver does as well - once they hit terminal velocity. $\endgroup$
    – Steve
    Jul 5, 2016 at 13:28

1 Answer 1


I've done a lot of reading on the topic of animals in space (see animals and life tags). I'm pretty confident in concluding that no mammal has beaten Valeri Polyakov's record of 14 months (437 days 18 hours). Popular Science seems to indicate that as of 2015 a month is the longest any mammal other than a human has been in space, and that record is held by mice.

  • $\begingroup$ Makes me wonder why not leave them for duration between crew changes (7 months) and bring them back down with a Soyuz? $\endgroup$
    – SF.
    Jul 19, 2018 at 21:06

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