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Saturday Science: Bag of Bones

Saturday Science: Bag of Bones

At this point in history, about 550 humans have traveled into space. Scientists and space agencies like NASA define “space” as 100 kilometers (about 60 miles) above the surface of the Earth, and the great majority of the people who have gone that high are astronauts. A few were Air Force pilots who flew right up to the edge of space before coming down to Earth. A very select few, the men of the Apollo program, traveled about 386,000 kilometers (~240,000 miles) away from Earth to get to the moon. Many more, though, have spent weeks or months on the International Space Station.

The astronauts aboard the ISS face a unique issue: spending a long time in microgravity is hard on their bones. They get weaker the longer someone is in space, and scientists still aren’t quite sure why. This means that when an astronaut returns to Earth, they’re more likely to suffer bone fractures than someone who’s never left. Probably still worth it, though.

Today’s experiment will give you an idea of what happens to bone tissue in space, and why it’s such a big problem for astronauts when they come back down to Earth.


  • 2 Ziplock snack or sandwich bags
  • Corn puff cereal
  • Permanent markers
  • A heavy book


  1. Fill one of your Ziplock bags with cereal. Make it as full as you can and still be able to completely close it up. This bag represents healthy bone tissue: dense and packed-in, with some open space, but still pretty tough.
  2. Fill your other bag so it’s only about half as full as your first one and seal it up. This bag represents bone tissue that has suffered significant loss, like after a long stretch on the ISS.
  3. Place your healthy bone bag on a table or on the floor (really, any flat surface will do).
  4. Pick up your book. You’re going to use this book to represent a shock to the bone, like a fall or a hard bump.
  5. Hold your book about 2 feet above your healthy bone bag with the cover facing down so the widest part of the book contacts the bone. Drop it.
  6. If gravity and physics are still working, you should have some damaged bone. Put it aside for now, because we need to repeat the previous few steps with your unhealthy bone bag. Before you do, though, make a prediction: will the results be different with the 50% bone bag? How? Now place the bag on your flat surface, hold the book up to the same height as before, and drop it.
  7. Make some observations. What is different between the two bags? You used the same book and dropped it from the same height, so what might account for those differences?


You probably noticed that your healthy bone bag suffered a lot less damage than your 50% bone bag. There was more cereal/bone tissue there to resist the force of the book, and it was able to basically push back better and not get hurt quite as badly. On the other side, we have your weak bone bag, which had way less tissue and basically wasn’t able to defend itself as well when that book dropped down. Had these been real bones suffering a real shock, the weak bone bag would have been far more likely to break than the healthy one. This is what astronauts have to deal with after a long time in space. Heck, it doesn’t even have to be that long; bone loss can begin after as short as 1 week spent away from Earth’s gravity.

When bone gets weakened as it does in space, scientists and doctors refer to a loss of “bone density.” This means that the tissue isn’t as thick and packed together as it used to be; it’s being weakened from the inside. The term for this is osteoporosis. It happens on Earth, too, and you may know someone who has it. It affects many people as they age and their bone tissue begins to break down faster than it can be rebuilt.

One of the factors causing osteoporosis in astronauts is that they just don’t use their bones as much. On Earth, bones are under constant stress because we’re all constantly moving while gravity pulls on us. In space, the astronauts do a lot of floating, and the hours of exercise they do while strapped down to mimic gravity just aren’t quite the same. There are probably other factors, too, though, since a recent NASA study found that fish sent to space suffered the same amount of bone loss, and fish are constantly swimming through water, which provides activity and stress on their bones even in space.

Figuring out all of the factors leading to space osteoporosis, and how to address them, is a major project for scientists who are working on getting humans back to the moon and eventually to Mars. If we don’t get it figured out, such long-term space voyages may be out of reach.

But you know what? Even with the bone loss, I still might risk it to be able to get out there into the great dark expanse of outer space.

This activity has been adapted from a NASA educational activity also called “Bag of Bones.”

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