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Sibling Rivalry: A Mars/Earth Comparison

Earth and Mars Comparison

Mars and Earth Comparison. Click image to see animation. Credit: NASA

Scientific understanding is often a matter of making the right comparisons. In terms of studying the Earth, one of the best comparative laboratories exists one planet over -- on Mars. In many ways, the study of Mars provides Earth-bound scientists with a control set as they look at the processes of climate change, geophysics, and the potential for life beyond our own planet.

In January of 2004 NASA landed two extraordinary research probes on Mars as part of an international armada of exploratory vehicles sent to Earth's dusty neighbor. Much of the technology and scientific methodology built into those missions directly relate to the sophisticated research efforts currently being used to study our own planet.

The Big Picture: Different but Not Dissimilar

The similarities are striking. Each planet has roughly the same amount of land surface area. Atmospheric chemistry is relatively similar, at least as Earth is compared to the other planets in the solar system. Both planets have large, sustained polar caps and the current thinking is that they're both largely made of water ice. The sibling planets also show a similar tilt in their rotational axises, affording each of them strong seasonal variability. The neighbors also present strong historic evidence of changes in climate. In these images, we see both planets in true color first, then draped in false color, showing relative altitudes of surface features. Blues indicates low features; reds and whites indicate high features. (Click image above for animation)

Olympus Mons: A Martian Peak with a View

Earth is a planet constantly re-making itself. A vibrant climate, an active water cycle, and a dynamic interior reshape and redefine our home everyday, sometimes dramatically. In terms of topography, some of Earth's biggest changes come from moving tectonic plates floating on the planet's mantle, and volcanoes -- huge outflows of heat and matter from deep inside the Earth's crust.

Image of Earth

Mountains on Mars are much larger than Earth mountains. Click image to see animation comparing Mars and Earth peaks. Credit: NASA

But while Earth's features eternally change, they do not persist with the same permanence as features elsewhere in the solar system. For a particularly interesting comparison, we look to Mars.

In the entire solar system, Mars boasts general features that are some of the biggest, widest, and deepest. One of its standouts is the immense Olympus Mons, a volcano of such size and scale that it’s own peak reaches above most of the Martian atmosphere. Olympus Mons could not even exist on Earth; with Earth's stronger gravity field, the massive volcano would collapse under its own weight if it were here.

The Martian giant rises about 23 kilometers from the surrounding plains. On Earth, the closest thing resembling this volcanic giant is the Mauna Loa peak on Hawaii, which rises about 10 kilometers from its base on the floor of the Pacific Ocean. Both of these mountains are dramatically taller than the Himalayan Mt. Everest. But Mt. Everest is not a volcano; both Mauna Loa and Olympus Mons are. Their histories are described by dramatic deliveries of molten material to the surface of each planet from their respective interiors. In this sequence we see the two planets in several color schemes. We begin by flying into the Earth in true color. Then we remove the water and look at the topographic features of the planet from the ocean floor in false color, where blues indicate low points and reds are high. Next we overlay a true color, semi-transparent Olympus Mons on top of the Hawaiian Islands to provide a true-to-scale comparison of their relative sizes. Finally we pull back to see the whole of the Martian globe in true color. (Click image above for animation)

Magnetic Signatures


Solar storms impact the Earth and Mars differently. Click image to see animation . Credit: NASA

Mars does not have the same kind of magnetic field as Earth. But evidence collected by the Mars Global Surveyor (MGS) indicates that the planet may have once had a global magnetic field, generated by an internal dynamo. Evidence suggests that the planet’s magnetic field reversed direction, or flipped, several times in its early days as conditions in the mantle and core of the planet changed. But that dynamo faded, leaving only faint traces of its magnetic past locked in the Martian crust.

Scientists continue to explore these processes on Mars and how they relate to magnetic processes on Earth. And speaking of home, Earth's magnetic field is powerful: powerful and profoundly important to everyone who lives here. It not only shows evidence of pronounced poles, but also clearly identifiable field lines -- magnetic lines of force that define an intangible bubble of electromagnetic energy around the planet. The magnetic signature that defines the field around Earth acts like a protective shield from harmful solar and cosmic radiation. In many ways, the magnetic field is as much a defining characteristic of our planet as any of its other significant attributes. Not only does it protect the Earth from extraterrestrial radiation, but it also may have helped the Earth both hold on to its atmosphere and water. (Click image above for animation)

Water Warehouses - Polar Caps May Reveal Planetary Histories

Polar caps on Mars and Earth

Polar caps on Mars and Earth are very similar. Click image to see animation . Credit: NASA

Both the northern and southern Martian ice caps vary in size as its seasons change. Scientists believe that the permanent northern ice cap is mostly frozen water while the southern cap is frozen water and carbon dioxide. Shown here the northern ice cap extends over a sizeable portion of the planet's pole, rippling and folding as ice and snow merge together. Its non-seasonally affected size is several times greater than its southern counterpart.

On Earth much of the planet's fresh water is locked up in ice covering the two poles. This helps preserve a delicate balance in oceanic chemistry as well as relative temperature stasis for the planet. In the opposite corner of the screen we're looking at Antarctica, surrounding Earth's South Pole. And while polar ice, plus the vast ice sheet covering Greenland in the north may only represent roughly three percent of the overall water contained on Earth, it represents two thirds of all the available fresh water -- water that's vital to many of the myriad lifeforms found here. (Click image above for animation)

Data now indicate that Mars' northern polar region may contain as much water as all that's contained on Greenland's ice sheet -- a vast tract of frozen water that's up to three kilometers thick in some places.

For more comparisons between Mars and Earth visit NASA Goddard Space Flight Center

Related Links:

NASA's Mars Exploration Rover Mission

The Earth Science Enterprise

NASA's Earth Observing System

The Earth Observatory

Michael Starobin and Mike McClare
NASA Goddard Space Flight Center