Earth & Mars: Similar but Different

Try to think back in time to your younger years. The period when life was simpler and you would gaze up at the darkened sky at night and wonder if there was anybody else out there in the vast void of space. You would watch Han Solo and Luke Skywalker travel immense distances at the speed of light. They would engage in space wars spanning the far reaches of a fictitious galaxy. Intelligent life was abundant and not limited to just one planet. As with most Hollywood action adventure movies, “Star Wars” was fictitious and heavily dramatized, but is it possible for life to exist on planets other than Earth? Obviously, our home planet is rich with growing organisms that seemingly occupy every square inch of available space. What about the other planets in our galaxy, the Milky Way. If there is a planet most suitable for sustaining life, it would surely have to be Mars. Earth and Mars are similar in many respects; however, they are quite different from each other and both have their unique qualities.

While Earth is the third closest planet to the Sun and fifth largest, Mars is the fourth closest and seventh largest planet. It is more brilliant than any object in the sky less the moon, Venus, and the Sun. There are no other planets that display as many qualities as ours than Mars does. The red planet was named after the Greek God of War, in part to its striking red color. If you were to look at Mars through a moderately powerful telescope, under good conditions, you would notice a considerable amount of detail. Included in that detail would be one of Mars’ two polar caps. The snow on these caps is not made up of water though. In fact, water cannot exist as a liquid on Mars. It is carbon dioxide snow that covers the Martian caps, however, under the snow lies water in the form of ice. One interesting fact about these polar caps is that they are the same size as the polar ice caps on Earth, relative to the planets’ size. Winter in the northern hemisphere corresponds to summer in the southern hemisphere; the relationship between hemispheres causes the northern cap to grow while the southern cap diminishes. Half a year later (306 Earth days) the situation is reversed. When it reaches its maximum size, the sourthern polar cap covers a larger area than that of the northern cap. You might ask why this is so. The reason is that the autumn and winter is longer in the southern hemisphere than in the northern hemisphere. While the caps are forming, white clouds cover them so that the caps themselves are barely visible. Just before spring arrives, the clouds begin to life exposing the newly formed snow caps.

Because Mars is farther from the Sun, its orbit is slower than Earth’s is. Mars travels 24 kilometers per second around the Sun opposed to Earth’s 29.8 kilometers per second. Though it moves only slightly slower; it takes approximately 687 Earth days to complete one full revolution around the Sun. Therefore, a Martian year is almost twice as long as Earth’s. Unlike the seasons of Earth, the Martian seasons are not equal to one another. The seasons range from 146 days of the northern autumn to 199 days of the northern spring. This can be accounted for by the elliptical shape of Mars’ orbit. The path that Earth follows around the Sun is more circular resulting in seasons that are equal in duration. Winter in Mars’ northern hemisphere are both shorter and warmer; summer is longer and cooler. The opposite is true for the southern hemisphere; winter is longer and colder, and summer is shorter and hotter. Remarkably, this scenario is the same for Earth’s northern and southern hemispheres. The longer spring and summer in the northern hemisphere of Mars might have you thinking that the summers are hotter than those in the southern hemisphere. This is incorrect, however, because the Sun is farther away from Mars when the northern hemisphere is tilted towards it. Noted in Earth time, the length of time it takes for Mars to complete one full rotation on its axis is 24 hours 37 minutes and 22.67 seconds. Since the days are approximately the same on Mars as they are on Earth, but the average time it takes Mars to orbit the Sun is more than Earth’s; Mars moves a smaller distance in its orbit than Earth does in the same amount of time.

Similar to that of the Moon, Mars does not have active plate tectonics, therefore, telltale signs such as folded mountains seen on Earth are nonexistent on Mars. With no lateral plate motion, hot-spots under the Martian crust stay in a fixed position on the surface. But there is no evidence of current volcanic activity. There is, however, new evidence from the Mars Global Surveyor that there may have been some tectonic activity in the early history of the red planet, making comparisons to Earth all the more interesting. As we all know, erosion leaves behind evidence of the gradual wearing away on a planet. Because of these signs, we know that a significant amount of erosion occurred on Mars including large floods and small river systems. Four billion years ago there may have been large lakes or even oceans on the planet’s surface.

Early in its history, Mars was much more like Earth. The lack of plate tectonics, however, disabled the red planet’s ability to utilize carbon dioxide to establish a greenhouse effect. Without a way to keep solar heat inside the planet’s atmosphere, the surface temperature drops to a point inhabitable for intelligent life. Mars’ atmosphere is composed mostly of carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%). The average pressure on the surface of Mars is only 7 millibars, which is less than 1% of Earth’s. The pressure varies greatly with altitude from 9 millibars in the deepest basins to 1 millibar at the highest point, Olympus Mons. Even though the pressure is considerably lower than that of Earth’s, it is still thick enough to support very strong winds and vast dust storms that on occasion engulf the entire planet for months. Maximum surface temperatures on Mars occur about an hour after midday and decrease rapidly, at first, and then more slowly after Sunset. The temperature on the surface may reach as high as 100Ëš C (180Ëš F) near the equator. During the night, there is no part of the planet where the temperature is above freezing, 0Ëš C (32Ëš F). As a result of the low nighttime temperatures, a large amount of the water vapor in the atmosphere condenses as frost before Sunrise. It will vaporize again, and possibly melt into liquid water in certain locations during the daytime. Surface temperatures are higher during the winter in the southern hemisphere; the winter temperatures are conversely lower.

People have always seemed intrigued by the possibility of life on Mars. The thought ignites excitement at the notion that we aren’t they only life forms living on a planet. There are certain requirements that must be met for humans to inhabit a planet. Temperature, light, gravity, atmospheric composition and pressure, and water are all necessary to sustain life. Obviously, all of these criteria have been met for us on planet Earth or you wouldn’t be reading this essay right now. Mars, however, does present some extreme conditions which may prevent life from ever existing on the red planet. The temperatures during the night are very low as mentioned earlier; this simply means that any enclosed structures would have to be heated at night. This feat would not be terribly difficult if there is sufficient insulation. Humans need light to see and plants need it for photosynthesis. The average amount of light falling on Mars is roughly the same as that falling on Earth. In fact, due to Mars’ less dense atmosphere, there are probably less clouds on Mars. The only major difference between the solar radiation falling on the surface of Earth to that of Mars is the greater amount of ultraviolet in the latter. UV rays are harmful to all organisms, plants and animals. Protection from this kind of light would be accomplished through the use of materials which would absorb the ultraviolet light. The force of gravity needs to be neither too great or too small on a planet. With a gravitational acceleration of about 38% of that on Earth, the gravitational conditions on Mars should be quite tolerable. An artificial atmosphere would have to be constructed to combat the unsuitable pressure and composition of Mars’ natural atmosphere. Oxygen would be extractable from the different forms of ferric oxide believed to be present on the surface of Mars. A more practical approach would be to take advantage of the abundant supply of carbon dioxide. The plants would then use the gas in the process of photosynthesis; thereby, emitting oxygen as a waste product. The adequate supply of water presents one last problem. Since water is the primary building block of all life, without it colonization would be impossible. In all likely events, many materials, including water, would have to be brought from Earth to Mars. We are fortunate enough to have all of these requirements available to us on our home planet. Except at the north and south poles, the daily and nighttime temperatures of Earth are quite tolerable. There is more then enough light available for humans and animals to see by day and for plants to thrive. The ozone layer, high in the atmosphere, shields us from the Sun’s harmful UV rays. The force of gravity on Earth is one that is not too strong, weighing us down, nor is it too weak causing us to float up into the atmosphere. Perhaps one of the biggest factors differentiating Earth from Mars or any other planet is the existence of water in a liquid form. Water is fundamentally important; it causes the weather to change, enables plant growth, and is the building block of all life.

Even though each planet has their own distinct characteristics; both Earth and Mars share some similarities. Both have roughly the same overall surface temperature. Seasons of the same type occur in each of the planets’ two hemispheres. Just like the Earth, there is a difference between the northern and southern hemisphere. Almost all of the massive volcanoes lie in Mars’ northern hemisphere while the prominent basins are located in the southern hemisphere. On Earth, most of the great oceans lie south of the equator and all of the major land masses can be found north of the equator, in the northern hemisphere. Their likenesses certainly do not shadow their differences; the lack of water on Mars sticks out like a sore thumb. The color of Mars is another quality that is quite dissimilar than that of Earth’s. These two planets seem to be related like brother and sister, and like many siblings, they each posses qualities that are unique to themselves; there are also many properties shared between the two. Earth and Mars appear to be the same, but closer examination reveals each has their own personality causing each one to be quite different from each other.

American, Scientific. The Planet Earth. New York, NY: Simon and Schuster, Inc., 1957.
Attenborough, David. The Living Planet. Boston, MA: David Attenborough Productions LTD., 1984.
Cross, Charles. Mars. New York, NY: Crown Publishers, Inc. 1973
Gamow, George. A Planet Called Earth. New York, NY: The Viking Press, Inc., 1963.
Glasstone, Samuel. The Book of Mars. Washington, D.C.: NASA, 1968.
Moore, Patrick. Mars. New York, NY: Crown Publishers, Inc., 1973.

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