Introduction to How Mars Works

Mars has fascinated us for years. From the time astronomers first turned their telescopes on the planet shining in the night sky, we have imagined life there. Unlike our other planetary neighbor, Venus, which remains shrouded in cloudy mystery, the red planet has invited speculation and exploration. The U.S., the former Soviet Union, Russia and even Japan have launched spacecraft destined to land on or orbit Mars since the 1960s. Meanwhile, Earth-bound scientists keep their fingers crossed for more information about the red planet.

The successful missions, like the very first Mars flyby in 1964 by the U.S. Mariner 4, have provided a treasure trove of data and, of course, introduced many new questions. Recently, those data, compliments of spacecraft such as the Phoenix Mars Lander, the Spirit and Opportunity rovers, and the Mars Global Surveyor orbiter among others, have been arriving at Earth at a dizzying rate. It seems like a golden age for Mars exploration.

­Here­'s what we've learned about the fourth planet from the sun while orbiting it, landing on it and sampling its contents: It's cold, dusty and dry, but that probably wasn't always the case. Ample data seem to point toward liquid water rushing over its surface in the form of lakes, rivers and an ocean at some undetermined point in the past. Traces of methane have been detected in the atmosphere, but the source is unknown. On Earth, much of the methane is produced by living organisms, like cows, which could bode well for the possibility of life on Mars. On the other hand, the gas could also have nonbiological origins, such as the Martian volcanoes.­

One thing we do know: Humans won't be walki­ng on Mars anytime soon. All manner of robots will be cruising its dusty surface long before we do, including possibly some inflatable, lightweight probes that will roll around and gather data.

The next best thing to exploring Mars is reading about it, right? So get ready for to launch into the fascinating world of the red planet. How did it form? What's the weather like? And most important, has water or life on Mars ever existed?

Read on to find out why early astronomers erroneously thought canals crisscrossed the planet, like an extraterrestrial Venice.

Mars History

As you can see from the image below, Mars has few distinguishing features when viewed from Earth, even with the best telescopes. There are dark and light areas, as well as polar ice caps, but certainly not the clear features that you can see in images from orbiters around Mars. Therefore, we can excuse early astronomers for making mistakes or embellishing their observations. To these scientists searching the sky, Mars was a vastly different world than we know today.

In 1877, Giovanni Schiaparelli, an Italian astronomer, was the first person to draw a map of Mars. His map showed a system of streaks or channels, which he called canali. In 1910, the U.S. astronomer Percival Lowell made observations of Mars and wrote a book. In his book, Lowell described Mars as a dying planet where the civilizations built an extensive network of canals to distribute water from the polar regions to the center of the planet.

Although Lowell's book captured the public's imagination, the scientific community summarily dismissed it because his observations weren't confirmed. Nevertheless, Lowell's writings sparked generations of science fiction writers. Edgar Rice Burroughs of Tarzan fame wrote several novels about Martian societies, including "The Princess of Mars," "The Gods of Mars" and "The Warlord of Mars." H.G. Wells wrote "The War of the Worlds" about invaders from Mars (Orsen Welles' radio play of this book caused a national panic in 1938).

These two think goggles will protect them from Martian invaders in Hollywood's adaptation of "The War Of The Worlds."

Getty Images

Hollywood has also fueled the public's fascination with the planet in films such as "The Angry Red Planet," "Invaders from Mars" and, more recently, "Mission to Mars" ­and "Total Recall," a futuristic mega-hit that featured Arnold Schwarzenegger leading dual lives on Earth and Mars.

In the 1960s and 1970s, however, the U.S. Mariner, Mars and Viking missions started sending back images of a very different world from that described by Lowell and his fiction and silver-screen successors. The photos, snapped during flybys of the planet and eventually during the Viking landings, showed Mars as a dry, barren, lifeless world with variable weather that often included massive dust storms that could whip across a majority of the planet. So with thousands of photos as evidence, Mars was confirmed as a rust-colored, desert planet with rocks and boulders, rather than the home of irritable Martians and man-eating plants a la "The Angry Red Planet."

Now, we have extensively mapped the planet's surface with Mars Global Surveyor, sent rovers to bump over its surface and scoop up soil samples, and launched orbiters to observe the planet from space. More missions are in the works. NASA has committed to an extensive program of robotic and possibly human exploration of Mars.

So far these missions have enabled scientists to hazard a theory about how the red planet formed, and the story would actually make a pretty good movie. Read on to learn how solar collisions gave the Earth its next-door neighbor.

The Origins of Mars

Unfortunately, no human geologist has been to Mars. So the best information that we have about the planet's beginnings 4.6 billion years ago come from images taken by orbiters and landers, Martian meteorites, and comparisons with its planetary peers (Mercury, Venus, Earth and Earth's moon). The current theory goes like this:

1. Mars formed from clumping or accretion of small objects in the early solar system.
2. There was a period of intense bombardment from meteors.
3. The hot mantle pushed through and lifted portions of the crust.
4. One or more periods of intense volcanic activity and lava flows followed.
5. The planet cooled and the atmosphere thinned.

Let's look at these steps in more detail.

Mars was created by the accretion of small objects in the early solar system, which took about 100,000 years. Mars grew and developed a larger gravity field, which attracted more bodies. These bodies would fall into Mars, impact and generate heat. The continued accretion of impacting material and the heat generated caused the material to sort itself out into a core, mantle and crust. Gases released from the cooling formed a primitive atmosphere.

But as Mars formed, it couldn't catch a break. It was heavily bombarded by meteors in the inner solar system. These bombardments produced craters and multi-ring basins all over the planet, like the 1,400-mile (2,300-kilometer) wide Hellas Planitia impact crater in the planet's southern hemisphere. Some geologists think that a huge impact occurred that thinned the crust of the northern hemisphere. Similar impacts occurred on Earth and our moon at this same time. On Earth, the craters were eroded by wind and water. On the moon, the evidence of these great collisions is still visible.

Now imagine Mars is a soft-boiled egg; the inside is hot as the shell cools. If the shell is weak in spots, the egg will crack and the cooked yolk will protrude. A similar occurrence happened with the Tharsis region, a continent-sized land mass in the southern hemisphere. The hot mantle bulged out, pushing up the crust and fracturing the surrounding lava plains (forming Valles Marineris, a network of canyons). In other spots, the mantle pushed through the crust, giving rise to the region's many volcanoes, such as Olympus Mons. (We'll talk about all these Martian landmarks next.)

During this period, there were widespread volcanic eruptions. Lava flowed from volcanoes and filled the low-lying basins. Eruptions released heat gas that contributed to a thick atmosphere, which could have supported liquid water. Therefore, there might have been rain, flooding and erosion. The erosion would produce sedimentary rocks in the basins and plains, and form channels in the rock. More than one period of widespread volcanic eruption may have occurred during Mars' history, but eventually the volcanoes stopped rumbling as much.

The bulges that caused the crustal uplifts and the widespread volcanic activity released vast amounts of heat from the inside of Mars. Since Mars isn't as large as the Earth, it cooled much faster, and the surface temperature cooled with it. Water and carbon dioxide from the atmosphere began to freeze and fall to the surface in vast amounts. This freezing removed large amounts of gas from the atmosphere, causing it to thin. In addition, any surface water may have frozen into the ground, forming permafrost layers. Intermittent volcanic eruptions would release more heat that would melt more water ice and cause flooding. The flooding would erode channels and carry more material down to the surrounding plains.

While this is the current theory about the origin o­f Mars, it needs more data to back it up. Learn what the Mars rovers and other spacecraft have discovered about its dry and dusty, but certainly not monotonous, surface next.

The Surface of Mars

We can divide the surface of Mars into three major regions:

1. Southern highlands
2. Northern plains (both the plains and the crustal upwarps)
3. Polar regions

The southern highlands are extensive. The region's elevated terrain is heavily cratered like the moon. Scientists think the southern highlands are ancient because of the large number of craters. Most cratering in the solar system happened more than 3.9 billion years ago, at which point the rate of meteors bashing into the solar system's planetary bodies dropped steeply.

The northern plains are low-lying regions, much like the maria, or seas, on the moon. The plains show lava flows with small cinder cones -- evidence of volcanoes -- as well as dunes, wind streaks, and major channels and basins similar to dry "river valleys." There is a distinct change in elevation, of several kilometers, between the southern highlands and the northern plains.

Two continent-sized, high regions called crustal upwarps spread over the northern plains. In these upwarps areas the molten rock from the interior mantle pushed up the planet's thin crust, forming a high plateau. These regions are capped with shield volcanoes, where molten rock from the magma broke through the crust. The smaller region, named Elysium, is in the eastern hemisphere, while the larger one, called Tharsis, is located in the western hemisphere.

The highest point in the solar system that we know about rises up in the Tharsis region. This shield volcano called Olympus Mons (Mt. Olympus from Greek mythology) towers 16 miles (25 kilometers) above the surrounding plains, and its base spans 370 miles (600 kilometers). In contrast, the largest volcano on Earth is Mauna Loa in Hawaii, which rises 6 miles (10 kilometers) above the ocean floor and is 140 miles (225 kilometers) wide at its base.

Centered Image: mars-Olympus-mons3a.jpg

Topographic view of Olympus Mons

Photo courtesy NASA/MOLA Science Team

At the edge of the Tharsis region is a large system of canyons called Valles Marineris. Valles Marineris is 2,500 miles (4,000 kilometers) long. That's greater than the distance from New York to Los Angeles. The canyons are 370 miles (600 kilometers) wide and 26,400 feet (5 to 6 miles or 8 to 10 kilometers) deep. That makes Valles Marineris much larger than the Grand Canyon. Unlike our national landmark, which formed from water erosion from the Colorado River, Valles Marineris was created by the crust cracking when the Tharsis bulge formed.

Valles Marineris cuts through the surface of Mars

NASA/Arizona State University/Getty Images

We can see the polar regions from the Earth. Surrounded by vast dunes, the northern and southern polar ice caps seem to be made mostly of frozen carbon dioxide (dry ice) with some water ice. The size of the polar ice caps varies with the season. In the summer, the carbon dioxide from the northern ice cap sublimes, revealing a sheet of water ice below. In fact, the water ice in this northern region is the reason why NASA sent the Phoenix lander there. With the help of its robotic arm, the Phoenix has dug down to the frozen layer and examined soil samples to investigate its composition.

Read on to dig a little deeper into Mars.

The Interior of Mars

­Let's compare the interior of the Earth with that of Mars. The Earth has a core with a­ radius of about 2,200 miles (3,500 kilometers) from the center to the surface. The core is made of iron and has two parts: a solid inner core and a liquid outer core. Radioactive decay in the core generates the heat. This heat is lost from the core to the layers above. Convective currents in the liquid outer core along with the rotation of the Earth produce the Earth's magnetic field.

Mars, the more petite planet, probably has a core radius between 900 and 1,200 miles (1,500 kilometers and 2,000 kilometers). Its core (shown as red in the figure to the right) is probably made of a mixture of iron, sulfur and maybe oxygen. The outer part of the core may be molten, but it's unlikely, because Mars has only a weak magnetic field (less than 0.01 percent of Earth's magnetic field). Although Mars doesn't have a strong magnetic field now, it might have had a powerful one long ago.

Surrounding Earth's core is a thick layer of soft rock called the mantle. What do we mean by soft? Well, if the outer core is liquid, then the mantle is a paste, like toothpaste. The mantle is less dense than the core (which explains why it rests above the core). It's made of iron and magnesium silicates, and it stretches about 1,800 miles (3,000 kilometers) thick (remember that the next time you're trying to dig a hole to China). The mantle is the source of lava that spews and trickles from volcanoes.

Like Earth, the mantle of Mars (shown as brown in the figure) is probably made of thick silicates; however, it's much smaller at 800 to 1,100 miles (1,300 to 1,800 kilometers) thick. There must have been convective currents that rose up in the mantle at one time. These currents would account for the formation of the crustal upwarps, such as the Tharsis region, the Martian volcanoes and the fractures that formed Valles Marineris.

On Earth, the crust's continental plates float over the underlying mantle and rub ag­ainst each other (continental drift). The areas where they rub are filled with cracks or faults such as the San Andreas fault in California. These areas of contact between plates experience earthquakes and volcanoes. On Mars, the crust is also thin, but isn't broken into plates like the Earth's crust. There is no evidence of active volcanoes or earthquakes on Mars, but there must have been volcanic activity at one time because we can observe lava flows from orbit.

Do you want to see all this for yourself? You might have difficulty breathing on Mars. Find out why next.

The Atmosphere of Mars

­­Of all the planets, Mars is our closest relation in terms of makeup (not distanc­e), but that's not saying much. And it certainly doesn't mean that the red soil is hospitable. The atmosphere of Mars differs from the Earth's in many ways, and most of them don't bode well for humans living there.

• It's composed mostly of carbon dioxide (95.3 percent compared to less than 1 percent on Earth).
• Mars has much less nitrogen (2.7 percent compared to 78 percent on Earth).
• It has very little oxygen (0.13 percent compared to 21 percent on Earth).
• The red planet has about 1/1000 as much water vapor (0.03 percent).
• It exerts only 7 millibars of pressure (Earth's atmospheric pressure is 1,000 millibars).

Because the "air" on Mars is so thin, it holds little heat. Most of the heat comes from the ground after it absorbs solar radiation. The thin air also is responsible for the wide, daily swings in temperature (almost 100 degrees Fahrenheit or 60 degrees Celsius). Martian atmospheric pressure changes with the seasons. During the Martian summer, carbon dioxide sublimes from the polar ice caps into the atmosphere, thereby increasing the pressure by about 2 millibars. During the Martian winter, carbon dioxide refreezes and falls from the atmosphere (carbon dioxide snow!), thereby causing the pressure to decrease again. Finally, because the Martian atmospheric pressure is so low and the average temperature is so cold, liquid water cannot exist; under these conditions, water would either freeze or evaporate into the atmosphere.

­The weather on Mars is pretty much the same each day: cold and dry with a chance of storms -- dust storms, that is. Light winds blow from one direction in the morning and then from the reverse direction in the evening. Clouds of water ice hover at altitudes of 12 to 18 miles ­(20 to 30 kilometers), and clouds of carbon dioxide form at approximately 30 miles (50 kilometers). Because Mars is so dry and cold, it never rains. That's why Mars resembles a desert, much like Antarctica on Earth.

During the spring and early summer, the sun heats up the atmosphere enough to cause small convection currents. These currents lift dust into the air. The dust absorbs more sunlight and heats the atmosphere further, causing more dust to lift into the air. As this cycle continues, a dust storm develops. Because the atmosphere is so thin, great speeds (60 to 120 mph or 100 to 200 kph) are required to stir up the dust. These dust storms spread across large regions of the planet and can last for months. You might think all the dust would be bad for the rovers traversing the surface, but the storms actually can clear off the dirt caked on their solar panels.

The photo on the left shows a dust storm brewing at about the 4 o'clock position and in the northern polar cap. Two months later, the planet's features are totally obscured by the dust.

Photo courtesy NASA Jet Propulsion Laboratory (NASA-JPL)

Dust storms are also thought to be responsible for the variable dark regions on Mars that are seen from ground-based telescopes, which were mistaken for canals and vegetation by Percival Lowell and others. The storms are also a major source of erosion on the Martian surface.

Is all that dust making you thirsty? Read on to find out about water on Mars.

Water on Mars

Liquid water is essential for life, at least here on Earth. Presumably, the same goes for arid Mars. Or that's the assumption governing NASA's "follow the water" strategy for Mars exploration. Following the water in this case will mean going underground or sampling it from the air, since the planet's low temperature and pressure mean water can only exist as ice or vapor.

Scientist don't think the liquid was always so scarce. Modern Mars may resemble a barren desert, but very early Mars may have been quite wet, judging from some of the geologic clues left behind. Floods may once have flowed over the planet's surface, rivers may have carved out channels or gullies, and lakes and oceans may have covered large swaths of the planet. Can't quite picture it? Visit Mono Lake in California, one of the world's oldest lakes at 760,000 years old and an average of 57 feet (17 meters) deep. Now imagine it without water and you'll have the Gusev Crater, a giant basin bisected by a dry riverbed that the Spirit rover searched for evidence of water.

Recently, scientists looked at high-resolution 3-D images of Mars taken in 2005 and compared them to pictures taken in 1999 of the same area. What they saw excited them. A series of bright, depositary streaks had formed in gullies during the intervening years. These streaks were reminiscent of flash floods that can carve away soil and leave behind new sediments on Earth. A bunch of streaks doesn't sound that monumental, but if water was the recent force behind them, that changes things. To learn more about the discovery, read Is there really water on Mars?

Liquid water may be in short supply, but frozen water isn't. The Phoenix lander is investigating the ice in the far north of Mars. The lander's robotic arm has dug down into the icy layer for soil samples, which it is analyzing with its onboard instruments.

Victory! The Phoenix lander successfully scoops Martian soil.

Credit: Phoenix Mission Team/NASA/JPL-Caltech/U. Arizona/ Texas A&M University

In fact, the lander has three main objectives, all of them water-related:

1. Study the history of water in all its phases.
2. Determine if the Martian arctic soil could support life.
3. Study Martian weather from a polar perspective.

Life on Mars?

This simple question has captivated millions of minds since the days of astronomer Percival Lowell. We're still no closer to a definitive answer. That doesn't mean we've stopped trying to answer it though. Since the days of the Viking landers, spacecraft have been carrying out tests for life processes, analyzing Martian soil for traces of water and looking for the release of gases such as carbon dioxide, methane and oxygen that might result from the activities of bacteria. These tests have seemed to show that the Martian soil was chemically active, but not biologically active.

It's possible that we need to revisit our idea of Martian life. Rather than egg-headed green aliens whizzing around in UFOs, we may have to be content with the possibility of much smaller organisms, like bacteria. Biologists have unearthed bacteria living in inhospitable environments on Earth, such as Antarctica, so they theorize that life also could exist in the cold desert conditions of Mars.

Tom Raymond/Getty Images

The guy on the left might be what you're picturing when you think about life on Mars, but the bacteria on the right are the more realistic possibility.

In fact, researchers discovered a species of bacteria that had been lying dormant for 120,000 years two miles below Greenland's ice [source: Heinrichs]. After melting the surrounding ice and filtering out larger bacteria, Chryseobacterium greenlandensis awoke from its frozen slumber and started multiplying. Scientists are hoping for a similar discovery within the red planet's polar ice caps. If that doesn't sound too exciting to you, remember that bacteria was the first life form here on Earth.

If you're not too picky about where the life originates, we may see life on Mars, compliments of our spacecraft. Although the U.S. and other countries involved in space exploration have pledged to refrain from contaminating celestial bodies, bacteria such as E. coli and potentially even Legionella have been found in the International Space Station [source: Society for General Microbiology]. The Phoenix lander undoubtedly provided a ride to hundreds of thousands of microbes, although NASA states that the lander must not harbor more than 300,000 bacterial spores total, and it took several precautions to ensure that the lander's robotic arm was clean [source: NASA].

Artist's rendering of a human Mars expedition

Photo courtesy NASA

Nevertheless, the prospect of bacteria in space isn't quite as exciting as those Martians. But if you're a believer, don't lose hope. The final answer to the question of life on Mars, as well as the answers to other Martian mysteries, may require humans to explore the red planet in person.

For more Mars madness, browse the stories and links on the next page.

Lots More Information

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• What if I went to Mars for a year to study the planet, how much food and water would I have to take with me to survive?
• How Terraforming Mars Will Work
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More Great Links

• NASA: Mars Exploration
• The Mars Society
• NASA's Haughton-Mars Project
• Caltech Mars Surface Research
• Mars Pathfinder: Science Results Directory

Sources

• Chaisson, Eric and Steve McMillan. "Astronomy Today." Third edition. Prentice Hall. 1999.
• Heinrich, Allison M. "Researchers at Penn State 'Awaken' Dormant Bacteria." Tribune-Review/Pittsburgh Tribune-Review. June 5, 2008. (June 17, 2008) http://www.redorbit.com/news/science/1417517/researchers_at_penn_state_awaken_ dormant_bacteria/
• Marks, Paul. "Inflatable robots could explore Mars." NewScientist.com. May 30, 2008. (June 9, 2008) http://space.newscientist.com/article/dn14028-inflatable-robots-could-explore- mars.html?feedId=online-news_rss20
• "Mars." Encyclopaedia Britannica. 2008. (June 9, 2008) http://www.britannica.com/eb/article-54235
• "Mars Rovers Sharpen Questions About Livable Conditions." Jet Propulsion Laboratory. Feb. 15, 2008. (June 9, 2008) http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20080215a.html
• "Mars." World Book at NASA. (June 5, 2008) http://www.nasa.gov/worldbook/mars_worldbook_prt.htm
• NASA. "Mars Extreme Planet: Earth/Mars Comparison." 2006. (June 18, 2008) http://mars.jpl.nasa.gov/facts/
• NASA. "Phoenix Landing: Mission to the Martian Polar North." May 2008. http://www.jpl.nasa.gov/news/press_kits/phoenix-landing.pdf
• Skinner, Brian J. and Stephen C. Porter. "The Dynamic Earth." Second edition. John Wiley & Sons, Inc. 1992.
• Society for General Microbiology. "Where Man Boldly Goes, Bacteria Follow."May 30, 2008. (June 18, 2008) http://www.sciencedaily.com/releases/2008/05/080528191418.htm ScienceDaily.