Cosmic Connection (18 page)

This in no way excludes life on Mars. It merely means that if there is life on Mars, it is not easily detectable over interplanetary distances. The same is true in reverse:
Photographic
detection of life on Earth in daylight from the vantage point of Mars is impossible, as we have found by studying several thousand orbital photographs of our own planet. But the time-varying streaks and splotches on the Martian surface are a new and most exciting Martian phenomenon, which cries out for further study.

Since the Martian changes occur slowly, the variable-features objectives required very long time intervals between two pictures of the same region to see what changes had occurred. At the very end of the mission, fifteen photographs were successfully taken by the
Mariner 9
cameras of regions in Syrtis Major and Tharsis, important for understanding the long-term variations. But when the time came to point the high-gain antenna of
Mariner 9
to the Earth, so that these pictures could be transmitted by playing back the spacecraft’s tape recorder, the last of the attitude-control gas was used up, Earth-lock could not be acquired, and playback did not occur. The spacecraft had literally run out of gas.

About a year before the
Mariner 9
mission was launched, the possibility was raised that the spacecraft would run out of control gas. A solution was proposed: That the propulsion tanks be connected to the attitude-control gas system–a kind of spacecraft anastamosis. Excess propulsion gas could then be used for attitude control in case the attitude-control nitrogen was exhausted. This possibility was rejected–largely because of its expense. It would have cost $30,000. But no one expected
Mariner 9
to last long enough to use up its attitude-control gas. Its nominal lifetime was ninety days–and it lasted almost a full year. The engineers had been overly conservative in assessing their superb product.

In retrospect, it sounds very much like false economy. With an adequate supply of attitude-control gas, the spacecraft might have lasted another full year in orbit around Mars. About $150 million of science might have been bought for $30,000 of pipe. Had we known that the spacecraft would die from a lack of nitrogen, I am almost certain that the planetary scientists involved would have raised the $30,000 themselves.

In fact, there are many such critical junctures in the space program where the addition of only a small amount of money can greatly increase the scientific return from a given mission. But NASA, severely limited by funding limitations imposed by Congress, the White House, and the Office of Management and Budget, has not had such small increments of money. If it were possible, and if a generous donor could be found, this would be a superb use for private philanthropy.

But these are idle musings. No anastamosis was performed; the final playback was not accomplished. Sitting there still on the
Mariner 9
tape recorder are fifteen vital photographs of the planet. They will never be returned under
Mariner
9’s own power. It has now also lost solar lock; sunlight is no longer being converted to electricity on its four great solar panels, and there is no way to reactivate it. We may never know what Tharsis and Syrtis Major looked like around the beginning of November 1972 from the vantage point of Martian orbit.

Or perhaps we will.
Mariner 9
is in an orbit that is slowly decaying in the Martian atmosphere. But the decay is so slow that the spacecraft will not crash into Mars for another half century. Long before then there should be manned orbital flights around Mars. Rendezvous and docking maneuvers are reasonably well developed in manned missions even now. Perhaps, then, sometime around 1990, as a small side-trip in a grand manned-orbital exploration of Mars, there will be a rendezvous with
Mariner 9
. The old and battered spacecraft will be taken aboard a large manned station and returned home–perhaps to be put in the Smithsonian Institution; perhaps to prevent terrestrial micro-organisms on
Mariner 9
from reaching Mars; but perhaps, also, to rescue and read off the fifteen lost pictures of the
Mariner 9
mission.

O
n our tiny planet, spinning in an almost circular orbit at a nearly constant distance from our star, the climate varies, sometimes radically, from place to place. The Sahara is different from the Antarctic. The Sun’s rays fall directly on the Sahara and obliquely on the Antarctic, producing a sizable temperature difference. Hot air rises near the equator, cold air sinks near the poles–producing atmospheric circulation. The motion of the resulting air current is deflected by Earth’s rotation.

There is water in the atmosphere, but when it condenses, forming rain or snow, heat is released into the atmosphere, which in turn changes the motion of the air.

Ground covered by freshly fallen snow reflects more sunlight back to space than when it is snow-free. The ground becomes colder yet.
When more water vapor or carbon dioxide is put into the atmosphere, infrared emission from the surface of the Earth is increasingly blocked. Heat radiation cannot escape from this atmospheric greenhouse, and the Earth’s temperature rises.

There is topography on Earth. When wind currents flow over mountains or down into valleys, the circulation changes.

At one point in time on one tiny planet, the weather, as we all know, is complex. The climate, at least to some degree, is unpredictable. In the past there were more violent climatic fluctuations. Whole species, genera, classes, and families of plants and animals were extinguished, probably because of climatic fluctuations. One of the most likely explanations of the extinction of the dinosaurs is that they were large animals with poor thermoregulatory systems; they were unable to burrow, and, therefore, unable to accommodate to a global decline in temperature.

The early evolution of man is closely connected with the emergence of the Earth from the vast Pleistocene glaciation. There is an as yet unexplained connection between reversals of the Earth’s magnetic field and the extinction of large numbers of small aquatic animals.

The reason for these climatic changes is still under serious debate. It may be that the amount of light and heat put out by the Sun is variable on time scales of tens of thousands or more years. It may be that climatic change is caused by the slowly changing direction between the tilt of the Earth’s rotational axis and its orbit. There may be instabilities connected with the amount of pack ice in the Arctic and Antarctic. It may be that volcanoes, pumping large amounts of dust into the atmosphere, darken the sky and cool the Earth. It may be that chemical reactions reduced the amount of carbon dioxide and other greenhouse molecules in the atmosphere, and the Earth cooled.

There are, in fact, some fifty or sixty different and, for the most part, mutually exclusive theories of the ice ages and other major climatic changes on Earth. It is a problem of substantial intellectual interest. But it is more than that. An understanding of climatic change may have profound practical consequences–because Man is influencing the environment of the Earth, often in ways poorly thought-out, ill-understood, and for short-term economic profit and individual convenience, rather than for the long-term benefit of the inhabitants of the planet.
Industrial pollution is churning enormous quantities of foreign particulate matter into the atmosphere, where they are carried around the globe. The smallest particles, injected into the stratosphere, take years to fall out. These particles increase the albedo or reflectivity of Earth and diminish the amount of sunlight that falls on the surface. On the other hand, the burning of fossil fuels, such as coal and oil and gasoline, increases the amount of carbon dioxide in the Earth’s atmosphere which, because of its significant infrared absorption, can increase the temperature of the Earth.

There is a range of effects pushing and pulling the climate in opposite directions. No one fully understands these interactions. While it seems unlikely that the amount of pollution currently deemed acceptable can produce a major climatic change on Earth, we cannot be absolutely sure. It is a topic worth serious and concerted international investigation.

Space exploration plays an interesting role in testing out theories of climatic change. On Mars, for example, there are periodic massive injections of fine dust particles into the atmosphere; they take weeks and sometimes months to fall out. We know from the
Mariner 9
experience that the temperature structure and climate of Mars are severely changed during such dust storms. By studying Mars, we may better understand the effects of industrial pollution on Earth.

Likewise for Venus. Here is a planet that appears to have undergone a runaway greenhouse effect. A massive quantity of carbon dioxide and water vapor has been put into its atmosphere, so cloaking the surface as to permit little infrared thermal emission to escape into space. The greenhouse effect has heated the surface to 900 degrees F or more. How did this greenhouse-overkill happen on Venus? How do we avoid its happening here?

Study of our neighboring planets not only helps us to generalize the study of our own, but it has the most practical hints and cautionary tales for us to read–if only we are wise enough to understand them.

S
tars, like people, do not live forever. But the lifetime of a person is measured in decades, the lifetime of a star in billions of years.

A star is born out of interstellar clouds of gas and dust. For a while, it stably converts hydrogen to helium in the thermonuclear furnaces of its deep interior. Then, in stellar old age, it encounters a set of minor or major catastrophes–a slow trickle or an explosive injection of star-stuff into space. During the more or less stable portion of the lifetime of the star, the hot interior region, converting hydrogen into helium, gradually eats its way outward from the very center. In the course of time, the star becomes slowly, almost imperceptibly, brighter.

After the flares and other impetuosities of its early adolescence, our Sun settled down to a more or less constant radiation output. But four billion years ago it was about 30 percent dimmer than it is today. If we assume that four billion years ago the Earth had the same distribution of land and water, clouds and polar ice, so that it absorbed the same relative amount of sunlight as it does today, and if we also assume that it had the same atmosphere as it does today, we can calculate what its temperature would have been. The calculation reveals a temperature for the entire Earth significantly below the freezing point of seawater. In fact, even two billion years ago, under these assumptions, the Sun would not have been bright enough to keep the Earth above the freezing point.