Future of Humans Inhabiting Other Planets

Life on Earth has evolved in lockstep with the evolution of the planet itself. It got started early; by some estimates some 3.9 billion years ago. Life as we know it now began in the seas and climbed onto the land some 570 million years ago. Five great periods followed to the current one where humanity evolved. In all of that time, life evolved according to the cycles of the Earth, which are many and varied. But the most important of all that has application to going forth and living on other planets is something called the circadian rhythm. This is the basic function that is tied to the Earth's rotation, the movement of the moon and the seasonal variation of the sun. It regulates our body chemistry so that human beings are alert during the day and asleep at night. This basic cycle works in lockstep with the rotation of the earth and the sun's daily transit from our point of view. This cycle is what we call the 24 hour cycle and we measure our days and lives thereby. The secondary cycle is linked to the moon and this one is about 25 hours. The two in combination causes approximate month long rises and falls in our general well being. The final great cycle is the annual one that we note where people vary from feeling up-beat in summer and depressed in winter. We know that all other life is affected one way or another by these planetary circadian rhythms. These measurable cycles of changes are so imbedded within us that we carry them into space. These imbedded cycles will influence us when we colonize the moon and Mars.

When the Mars explorer team that ran the Sojourner and Intrepid probe program on Mars, they had to adapt their lives to Mars' rotational cycle of about 25 hours. Within days, many on the team started to complain about symptoms similar to jet lag. Yet they had to continue the 25 hour day for the extent of the mission which actually went from months to years. Whole families were affected and those who had to also interface with our 24 hour day suffered the most. The two periods that began in sync, slipped further and further out of phase until the crew who worked days found themselves on the night shift in about a fortnight and then back again to days in another fortnight. Most people can adapt to a sudden change, as long as their circadian rhythm is not stressed for prolonged times.

People who are forced to work graveyard shifts and then switch to days suffer in a similar way. Flying from one time zone to another has a similar effect in making us feel dragged out. This is where the term jet lag comes from. This dragged out feeling can persist for weeks until the person has adapted. Now imagine being a lunar colonist. Almost everyone knows that the moon presents the same face to the Earth at all times and takes about 29 days to complete a set of phases. This means that in relation to the sun, the moon has a day that is 29 of ours in length. Now of course, colonists will probably follow a 24 hour rhythm, but they will be affected nonetheless by the sun's position in the lunar sky at all times. There is little doubt that they will feel a lunar version of jet lag in short order that will negatively impact performance.

It takes a lot of training and practice to personally juggle one's circadian rhythm and it also takes natural adaptation to a new environment. The latter may actually require several generations to accomplish. People who leave the Earth will leave behind all the circadian inputs that have been programmed by evolution into us for billions of years. Going forth into space is a huge and sudden change for a complex organism and it will take time to adapt to new planets.

Colonists on the moon and Mars not only have to deal with completely different environments on all fronts, they will lack the inputs of the rotational cycles of the Earth and the lunar influence. Now, for the lunar colonists, the Earth may provide a similar influence on the moon as the moon does on Earth. But this is a highly conditional may as the Earth will be found within a narrow patch of sky overhead or on the horizon at all times depending where one is on the moon. On the far side, the Earth will never be seen. Mars lacks the influence of a major moon but has two captured asteroids, Phobos and Demos. These present a strange daily spectacle as one will appear to progress from east to west and the other west to east. Other than that there is little influence other than the sun. If Mars had oceans, the tides would only be influenced by the sun.

Sunlight is weaker on Mars than on Earth and slightly stronger on the moon. The weaker sunlight on Mars will mean that agriculture will be more dependent upon plants that can get by on less light, such as shade loving plants. But colder temperatures there mean that a means will have to be in place to raise temperatures and perhaps even amplify sunlight. People will have to live in protective environmental suits (space suits) when venturing outside of a self contained facility. Being confined to a small area for several months, even several years will certainly contribute to a 'cabin fever' condition that those on Earth experience in regions like camps in Antarctica. This alone can drive a person 'up the wall' and do desperate acts. Then there are the 25 hour days, which will take a long time to adapt to. It may take several generations of children and grand children born on Mars to fully adapt. The best scenario overall for Mars is teraforming it into a more Earth-like environment.

Living in the asteroid belt is yet another scenario, where there are a lot of unpredictable conditions, among which is absent or very weak gravity. Human beings and all earthbound creatures evolved in a gravity field. We already know from all space missions so far that the human body will quickly adapt to a zero gravity environment by losing bone, muscle and heart mass. Special exercise techniques had to be invented as it were 'from the ground up' to duplicate the natural gravitational stress so that rapid body deterioration would be limited. Will we find similar problems on the moon, Mars and the asteroids? Yes; but to a lesser extent and if we intend to come back to Earth, we need to continually stress exercise to stay adapted to Earth's gravitational influence away from home.

The search for Earth like planets has heated up recently with new findings as of 2008-09. Of the 340 plus extra-solar system planets, a few close to Earth's mass have been found including one that's just 1.9 Earth masses. Located on the planetary system of Gliese 581 some 20.4 light years away, Gliese 581-e is a near Earth mass planet so close to its sun that it takes less than four days to orbit. It is totally unsuited for habitation as it is much closer to its sun than Mercury is to ours. But it holds out hope for others elsewhere. Another planet, in the same system, Gliese 581-c's orbit is mostly within the stars habital zone, but is substantially more massive than Earth. Its gravity alone would be prohibitive to exploration.

Eventually, an Earth mass planet will be found in a habital zone of a star. Where that planet is right now is unknown. Wherever it is, it will be a formidable task to get to it with current or evolving technologies as they exist. It could be anywhere from twelve to thousands of light years away. If and when we do get there, the conditions will be as far removed from what we have adapted to on Earth as living on Titan, Ganymede or Mars. Consider; the new found Earth would likely lack a moon. Its rotation may be much faster than Earth, closely matched or it may be tidally locked to its sun, presenting one side to eternal day and the other eternal night. The first humans there would have a tough time in the new environment. But given several generations, the children's children's children will adapt. Should they venture back to Earth, to them it would be an alien environment as all other planets are to us.

Perhaps the best solution of all is to live in space as we have learned to do with the International Space Station where we can control the environment to a great extent. We can take such a home with us and using all the techniques we have developed with increasing understanding, arrive reasonably healthy and maintaining our Earth born rhythms reasonably intact. We could reasonably visit many more stars even if they lack Earth like planets and live in space, dropping down to visit various planets for brief visits, like we did on the moon between 1969 and 1972. We could also send robot missions to scout out the various possibilities. Robots as far as we know are not locked into circadian rhythms except what we program them in or leave them out.