Shades of Gravity
Interview with Catharine Conley
Astrobiology Magazine (AM): Before you recently became NASA’s Planetary Protection Officer, you did research on the biological effects of gravity?
AM: Was that comparable to the results from your centrifuge studies?
CC: We never completed the centrifuge studies to the extent that I’d like to because we had to prepare for the space flight study. Our first space flight opportunity had a very rapid onset -- I only had a couple of weeks between being told I had the experiment and going on the shuttle.
But in the centrifuge experiment, we were able to show through gene expression that the centrifuge was altering their metabolism rather than just causing them generic stress.
AM: So it was affecting how they ate or processed energy?
CC: They were reproducing more slowly, so the cultures grew more slowly. After they came off the centrifuge, they moved very slowly. In additional control studies, we performed mechanical stimulation by growing worms in a shaking water bath. The worms in the centrifuge behaved in opposite ways from them. When you stopped the shaking water bath, those worms were hyperactive, but when you stopped the centrifuge, those worms moved more slowly than they should.
AM: How do you tell if a worm is just dizzy?
CC: (laughs) That’s a very good question. Worms don’t actually balance. They are always crawling on the ground; they don’t try to stand up straight. But they do have responses to mechanical stimulation. If you touch their noses, they’ll back up.
Our speculation was that perhaps the worms had the same sort of system. But because we were increasing the gravity in the centrifuge worms, causing them to be heavier than normal, they ramped down on their sensitivity. That might be why, when they came back to one G, they didn’t move.
AM: How long did it take them to get back to normal?
CC: Not very long. A couple of hours. That suggests it’s a protein expression phenomenon rather than a cell reproduction phenomenon or something that takes longer than that.
AM: Do you think we’re closer to understanding if humans will be able to live in different states of gravity?
CC: We haven’t had a chance to test it really, because we only have the microgravity of low Earth orbit, one gravity on Earth, and hypergravity from a centrifuge. Humans don’t survive very well in hypergravity because all the blood falls to your feet and your brain doesn’t get any oxygen. So you can’t make someone live in a centrifuge for years and years. Worms can live for months at 100 G, though, so they are much more resistant to gravity effects.
AM: What are other effects of reduced gravity on humans?
CC: One of the most obvious things is that because there’s less weight, your bones and muscles atrophy because they’re not resisting that weight. It’s the same thing that happens with prolonged bed rest. In addition, you have muscles in the veins of your legs, and when you stand up they have to pump the blood to get it back up to your heart. In microgravity the veins keep pumping, but there’s not enough gravity to pull the blood down. So astronauts end up looking puffy-faced in space -- they have more fluid above their heart because that pumping action is still going on. That also may be a contributing factor to space sickness.
Although it’s not well studied, there are some reports that intestinal function is different in microgravity. That’s another thing we can look at in worms, although we haven’t done it yet. It also has been reported that there are changes in the immune system, but it’s not clear whether that’s stress related, or related to a general metabolic shift, or whether they’re also related to the reduction of mechanical stimulation. There have been some studies of muscle cultures that show some form of atrophy.
AM: Other than the centrifuge or exercising in space, are there any other ways to counter the negative effects of microG?
CC: The type of exercise might make a big difference. There are some hypotheses that it’s the maximum impact rather than the total duration of the exercise that strengthens the bones and muscles. So perhaps astronauts should jump up and down instead of using the Stairmaster, for example. Other than exercises, there are some drugs we can use. We also have pressure suits to try to pull the blood back down to the feet, and that may benefit space sickness.
CC: Oh, I’m sure that partial G will be better than microG. We just don’t know what level is required for optimal health. It may be that if you’re on the Moon you’re somewhat better and if you’re on Mars you’re even better, but you really need to be on the Earth to be perfectly healthy. And that’s one of the other things we’re trying to explore with the worms – the adaptation over multiple generations to microgravity.
AM: In Kim Stanley Robinson’s books about the human colonization of Mars, he talks about how humans adapted to the lower G there wouldn’t be able to come back to Earth.
CC: That could happen if you have enough generations of reproduction and if you’re not adaptable enough. Humans can survive at 3 Gs. There’s about that much difference between Mars gravity and Earth gravity -- it’s only a relatively small fraction of one G. That suggests that even if you’re living on Mars for multiple generations, you could adapt to come back to Earth. It might be difficult, but it’s not going to take generations to adapt back, there probably will be some physiological adaptation but it’s not going to completely prevent you from returning. Although with the developmental aspects of human growth, such as bone development, it may require a lot of exercise and a lot of work to be able to come back.
I think Robert Heinlein also used that idea in his novels; it’s a recurring idea in science fiction and an interesting concept. Of course, if there were multiple generations of humans in microgravity, we know that’s different.
CC: It might be like cruise ships where they rotate out, or airplanes where you only have so many days of work. Certainly the astronauts or cosmonauts who have stayed up for a year or more have had some health problems.
AM: In the movie “Contact”, the rich guy, S.R. Hadden, goes on MIR because he says the low oxygen, microG environment slows the spread of his cancer. I wondered if that could be true, and if it would be beneficial to have hospitals in space.
CC: I would be surprised that cancer would grow more slowly in space simply because the radiation environment is much more harsh and would cause more mutations. It’s not unlikely that for cardiac problems it might be easier to live in space, because the heart doesn’t have to work against gravity to pump the blood around. And one of the problems with older people on Earth is they lie in bed a lot, so they get bed sores and other problems. I can imagine that people with arthritis or other problems with mobility might really enjoy being in space.