Space, Growing Old in

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Space, Growing Old in

Radiation and vacuum, large variations in temperature, and lack of oxygen make it impossible for humans to survive unprotected in space. Therefore, mini-ecosystems are needed to sustain life. But would there be any benefit to living and growing old in mini-ecosystems in space? Would the elderly live longer or suffer less from ailments such as arthritis?

On Earth, the direction of gravity (G) is perpendicular to the surface, and the intensity is 1 g . The intensity of gravity on the Earth's Moon is 0.17 g and on Mars it is 0.3 g. Even 200 miles away from Earth, the forward motion of a spacecraft counterbalances Earth's gravity, resulting in continuous free-fall around the planet with a resultant acceleration of about 10⁻⁶ g or 1 micro g. This is not weightlessness but microgravity .

Astronauts orbit the Earth in about 90-minute cycles and go through 16 day/night cycles every 24 hours. With the clock seemingly ticking faster and the reduced influence of g, what are the possibilities of growing old in space? Data collected so far indicate that the clock of living organisms ignores the 90-minute cycle and "freeruns" at slightly more than 24 hours, relying on the internal genetic clock. But microgravity also has more obvious consequences.

All life on Earth has evolved in 1 g and, therefore, has developed systems to sense and use g. Only by going into space can one fully understand how g has affected life on Earth. Biological organisms respond to changes in g direction and intensity. Plants grow and align with the direction of g. Humans change the direction g enters their body by changing position with respect to the surface of the Earth. For example, when standing up, g intensity (Gz) is greatest; when lying down, g pulling across the chest (Gx) is least intense.

The Effects of Microgravity on the Human Body

Microgravity is not a threat to life. Astronauts endure physical and psychological stresses for short periods of time and survive to complete a mission. The longer they live in space, however, the more difficult they find it to recover and readapt to Earth.

After less than five months on the Mir space station, David Wolf lost 23 lbs, 40 percent of his muscle mass, and 12 percent of his bone mass. It took one year to recover this bone mass. In space, adult humans lose 2 percent bone mass per month, compared to about 1 percent per year on Earth.

When astronauts return to Earth, long rehabilitation is needed: the weight of the body cannot be supported because of loss of calcium from bone; there is degradation of ligaments and cartilage in joints; and astronauts experience decreased lower limb muscle mass and strength. It is even hard to sit up without fainting because in microgravity blood volume is reduced, the heart grows smaller, and unused blood vessels in the legs are now no longer able to resist gravitational pull by pumping blood up towards the head.

Astronauts find that even standing and walking can be a chore. They may need to first walk with their feet apart for balance. Because the vestibular system in the inner ear that senses g and acceleration received no such input in space, leg movement coordination and proper balance are disturbed.

Exercise alone may not prevent adaptation to microgravity nor help maintain Earth-health-status to reduce this long rehabilitation.

One way to help astronauts prepare for the increased gravitational pull back on Earth may be to provide "artificial gravity" while on the spacecraft, using an on-board centrifuge for short exposures to g. Because the effects of microgravity are similar to the effects of prolonged exposure to Gx (the gravitational pull across the chest while lying in bed), tests on Earth have used healthy sleeping volunteers to mimic the effects of spaceflight micro-gravity, and the results have been used to research the best treatments.

On Earth, the symptoms astronauts suffer during spaceflight are associated with growing old. In astronauts the symptoms are fully reversible after their return to Earth. Their age has not changed, nor does it affect their life span back on Earth. In typical, earth-bound aging, however, these same symptoms are believed to be inevitable and irreversible. Because the symptoms are also seen after prolonged bed rest, it is believed that even healthy inactive people develop aging symptoms much earlier than had they been more active and used g to greater advantage.

If a human were to live in space forever, the body would adapt completely to microgravity. Some functions needed on Earth but not necessary in space would degrade or even disappear. Changes would progress until the body reached a new steady state, what would then be "normal" for space. At that point, the body may never be able to re-adapt to Earth.

On the other hand, consider someone on Earth with the same symptoms, pinned to a wheelchair by g —perhaps because of paralysis after a spinal cord injury. Such a person may experience tremendous freedom in being able to move about in microgravity using only the upper body as do the astronauts.

Would We Live Longer in Space?

These appropriate changes to the space environment tell us nothing about whether humans would live less or longer in space. To find out, scientists are using specimens with much shorter life spans. Experiments with fruit flies (Drosophila melanogaster ) exposed for short periods of their adult life to space and then studied back on Earth have shown no change in their life span.

Many genes related to aging in organisms like fruit flies and the roundworm (Caenorhabditis elegans ) are similar to the aging genes of humans. Because fruit flies and roundworms live 4–8 weeks, it is easier to study them in space both from birth and over several generations.

Markers of biological aging like telomeres studied extensively in aging research on Earth will also be studied in space. Telomeres are fragments of non-coding deoxyribonucleic acid (DNA; that is, DNA that does not give rise to proteins) found on the ends of each chromosome. When a cell divides, telomeres shorten until they eventually become so short that the cell can no longer divide and dies. The role of g and microgravity on such mechanisms may help unravel the mysteries of growing old both in space and on Earth.

So what is growing old? On Earth we use it to describe the debilitating changes that occur as one's age increases, eventually leading to death. Clearly, this does not apply to what happens in space, suggesting that perhaps growing old on Earth should be redefined. Space has taught scientists a great deal about growing old on Earth. The degenerative changes seen in astronauts and in humans aging on Earth indicate how important it is to be active and to use g to its fullest on Earth. In so doing, humans may live healthier, if not longer, lives.

see also Space Exploration; Spaceflight, History of.

Joan Vernikos