Explore! Mars: Inside and Out!

About Mars

Presentations: These are intended to provide background information for program providers, and not to be used directly in youth programs. These external resources are not necessarily 508 compliant.

  Next Stop: Mars (2 MB PowerPoint)
Drs. Walter Kiefer and Stephanie Shipp, The Lunar and Planetary Institute

  Mars: Shaping the Surface
Dr. Tomasz Stepinski, The Lunar and Planetary Institute

  Inside Mars
Dr. Walter Kiefer, The Lunar and Planetary Institute

  Exploring Mars (15 MB PowerPoint)
Drs. Walter Kiefer and Stephanie Shipp, The Lunar and Planetary Institute

  Current and Future Exploration of Mars (19 MB PowerPoint)
Dr. Walter Kiefer, The Lunar and Planetary Institute

  Exploring Mars: The Inside Story (6 MB PowerPoint)
Dr. Walter Kiefer, The Lunar and Planetary Institute

A Little About Mars

The Martian day, the time it takes Mars to spin once on its axis, is 24 hours and 40 minutes long, very similar in length to Earth's day. Its year is almost twice as long as Earth's, however. It takes Mars 687 Earth days to orbit the Sun. That path around the Sun is slightly more elliptical than Earth's, and the Sun is not exactly in the center of its orbital path.

Like Earth, Mars is tilted on its axis. This tilt, combined the elliptical orbit, contributes to seasons on Mars. Because Mars is closer to the Sun during its southern hemisphere summer, the summer in that hemisphere is warmer than the northern hemisphere summer.

Surface temperatures are cold — a warm summer day might reach 0°C (32°F), and winter at the poles can be as cold as –125 °C (–193°F), and its atmosphere is very thin. The atmospheric pressure at the surface of the planet is about 1/100th of that of Earth's. Mars' atmosphere is mostly carbon dioxide (95%), nitrogen (3%), and argon (2%), with trace amounts of other gases, like oxygen (0.15%). Earth's atmosphere is mostly nitrogen (77%) and oxygen (21%). The thin Mars' atmosphere offers little protection from dangerous incoming radiation, and, unlike Earth, Mars does not have an ozone layer to protect the surface from solar ultraviolet radiation.

Mars has massive dust storms — storms that can cover the entire planet! Wind speeds can reach 100 km/hour (62 miles/hour), stirring up the fine red dust. The dust gives the Martian sky a pinkish-tinge.

Image of dust storm on Mars.

A dust storm obscures the surface features on Mars
Image Courtesy of: NASA/JPL/Malin Space Science Systems

The Martian atmosphere contains much less water vapor than Earth, making clouds a rarity on Mars. There is no liquid water present at the surface. There may be frozen water in the ground, and Mars has ice caps in its polar regions that are a combination of carbon dioxide and water ice. Mars is about half the size of Earth. Because it has less mass, it has a smaller gravitational attraction. Surface gravity on Mars is less than 40% of Earth's. If you weighed 100 pounds on Earth, you would weigh 38 pounds on Mars.

How did Mars Form?

Mars formed at the same time our solar system formed, 4.6 billion years ago. Our solar system began when a cloud of dust and hydrogen and helium gases drifting in our galaxy started to condense and contract under its own gravity, forming a wide, flat, rotating disk. Most of the material collected in the center, condensing into a sphere of gas that eventually became our Sun. The remainder of the cloud formed a wide disk, swirling around the Sun, called the solar nebula. The rocky, terrestrial planets — Mercury, Venus, Earth, and Mars — all formed in the inner, hotter part of our Solar System, where metals and silicates were concentrated. Much of the gas and ice in the solar system could not exist as solids at the high temperatures in this region. So it was from the heavier materials that the rocky inner planets were made. The dust and particles collided, merged, and broke apart. Through the process of "accretion," these tiny particles formed larger and larger bodies, eventually becoming so massive that their gravity began to assist by attracting more and larger aggregates of material, speeding up the process of accretion. Because of this, the largest bodies grew the fastest, sweeping up material in their paths, and eventually becoming Mars and the other planets.

How has Mars Changed Through Time?

Mars has undergone several changes during its 4.6 billion year history — both inside and out!

Getting Organized Inside. Like all planets, Mars became hot as it formed, from the constant pummeling by impactors as it accreted, and from the radioactive decay of elements. Very soon after it formed, its interior melted or partially melted, and the materials making up Mars reorganized. The denser elements — iron and iron sulfide — separated from the more silicate-rich materials and sank to the interior, forming Mars' core. The silicate-enriched layer surrounding the core formed Mars' mantle. The least dense silicate materials formed the crust, perhaps crystallizing from a magma ocean that enveloped the planet. For the first few hundred million years, Mars probably had a magnetic field, generated by convection (fluid flow) in the molten core. As Mars cooled, the magnetic field died.

Image of Earth, Moon and Mars inner and outer cores.

Image showing cross-sections of the Earth, Moon, and Mars.
The crust in each case is a very thin outer layer.

The Great Dichotomy — or Why There is Such a Big Difference Between the North and South. In short, scientists don't know, but they are investigating it! A quick look at elevations on Mars shows that the northern hemisphere is relatively low or deep and the southern hemisphere is high. The crust in the southern hemisphere is about 25 kilometers (15 miles) thicker than in the northern hemisphere, and this causes the southern highlands to be about 4 kilometers (2.5 miles) higher in elevation than the northern lowlands. This evidently happened in the first few hundred million years of Martian history. The interesting problem is understanding why the crust is thicker in the south than it is in the north. Some scientists suggest that the northern hemisphere low is a depression created either by one giant asteroid impact or by several big impacts. Others suggest that motions inside of the mantle of Mars, known as convection, may have concentrated crust into the southern hemisphere. More information, gathered by spacecraft and by astronaut explorers, will be needed to solve this mystery.

Image of Mars Orbiter Laser Altimeter (MOLA) map showing elevations of the Martian Surface.

Mars Orbiter Laser Altimeter (MOLA) map showing elevations of the Martian Surface.
The northern hemisphere is low, while the southern hemisphere is high.

Making an Impact. Like all terrestrial planets, Mars has been significantly cratered. Our early solar system was a messy place; asteroids and comets large and small abounded. These space rocks struck the planetary surfaces, adding more heat, breaking up the outer planetary layers, and creating large bowl shaped depressions of shattered rock. With time, much of this debris was accreted into the planets, leaving their orbital paths relatively clear. By about 3.8 billion years ago, the period of intense bombardment came to a close, and impacts — though continuing even today - became smaller and less frequent.

Scientists expect impacts to strike all parts of planetary surfaces equally. The Moon and Mercury are cratered across their surfaces. If large area on a planet is not cratered, scientists interpret that this surface is younger than the more cratered areas; it has not had time to accumulate a large number of impacts. In other words, something has happened to that surface to erode or fill up the craters (or, in Earth's case, to regenerate the crust all together). The hemispheres of Mars are very different. The rugged Southern Highlands record the long history of impact events. The Northern Lowlands also are heavily cratered, but somethng has covered or buried most of them. leaving the surface smooth. Scientists are unsure exactly why the north and south are so different. Perhaps the craters have been filled by lava flows or covered by sediment, or eroded by flowing water. This is one of the big mysteries about the Martian surface.

For more information on impacts and craters, visit Impact Cratering.

Image of Mars Orbiter Laser Altimeter (MOLA) maps shows a distinction between lowlands and highlands.

Mars Orbiter Laser Altimeter (MOLA) maps show a distinction between Mars’ hemispheres. The northern lowlands are about four kilometers lower in elevation than the more heavily cratered highlands of the southern hemisphere. Image and caption courtesy of Planetary Science Research Discoveries.

Volcanism in a Big Way. Early Mars was volcanically active, spewing lava across its surface, and water and carbon dioxide into its atmosphere. Much of this early history, recorded in the older Southern Highlands, is obscured by impact craters.

From about 3.5 billion years until more recently, the volcanic — and tectonic — activity has been concentrated around the Tharsis region near the equator. Tharsis is a huge bulge in the crust, capped by prominent volcanos. Some scientists suggest the bulge overlies a region of hotter than normal mantle. The high temperatures allowed the development of numerous large volcanos. These volcanos thickened the crust, causing Tharsis to be higher than other parts of Mars. The crust was pulled apart to form the immense canyon of Valles Marineris more than 3 billion years ago.

Over 3000 km long and up to 8 km deep, Valles Marineris would stretch from Los Angeles, California to Washington, D.C. if it occurred on Earth. Image courtesy of NASA and the U.S. Geological Survey.

Olympus Mons, the tallest volcano in our solar system, began forming about 1 billion years ago. Scientists do not really know how young the most recent volcanic activity is on Mars. Certainly, some volcanos have erupted in the last 100 million years. Although that sounds like a long time, it is within the last 2% of our solar system's history! Some lava flows are so fresh and have so few craters, that they may be less than 100,000 years old. It is likely that some martian volcanos will erupt again in the future.

Olympus Mons, and the other volcanos of the Tharsis region, are 100 times more massive than volcanos on Earth! These volcanos are so large because Mars' outer layer does not move relative to the mantle underneath — the surface of Mars is stationary. The volcanos remain over chambers of molten rock and grow as lava flow after lava flow after lava flow pours out of the interior, each adding to the volcano.

For more information on volcanism, please visit Volcanism.

Olympus Mons (upper left) and volcanos on the Tharsis bulge. The white features are clouds. Image courtesy of NASA/JPL/MSSS

Moving Plates. There is no evidence that plate tectonics — the movement of rigid plates (lithosphere) on a mobile upper mantle (asthenosphere) — is occurring now on Mars. Mars lacks the pattern of features, such as chains of volcanos, long ridges, or folded mountains, that would be expected if plate tectonics were occurring or recent. All evidence is that Mars has had a stationary outer layer for at least the last 3 billion years, when the Tharsis region began to form. Recently, some scientists have speculated that Mars had plate tectonics in its early history, based on magnetic patterns in the Southern Highlands recorded from orbiting spacecraft. This is another area for scientific exploration.

Additional Information

  • For more information on tectonics and plate tectonics, visit Tectonism.
  • Explore additional information about the search for life on Mars, and Mars’ disappearing water and atmosphere at Life on Mars.

Get the solar system in your inbox.

Sign up for LPI's email newsletters