Mars Surface, Viking Data Mars Cutaway Moho Layer
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Some of Mars' best kept secrets, long buried beneath the surface of the red planet, were recently revealed by instruments on NASA's Mars Global Surveyor spacecraft.

New observations of Mars reveal that the planet's flat northern lowlands were an early zone of high heat flow that later may have been the site of rapid water accumulation, according to a view of the Martian interior generated using data from Mars Global Surveyor (MGS) spacecraft. Elevation and gravity measurements, which have been used to probe beneath the surface of Mars, indicate a period of rapid cooling early in Martian history, and evidence for large buried channels that could have formed from the flow of enormous volumes of water.


Table Of Contents

Revealing a Planet - Observations and Inferences Describe Martian Features

MGS Spacecraft Measuring Topography Measuring Gravity
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Researchers using data collected by the Mars Orbiter Laser Altimeter (MOLA) and a clever radio science experiment combined their findings and generated an entirely new map of the planet, providing the first measurements of Mars's crustal thickness. These measurements were inferred by the combination of two observational data sets, namely surface topography and the planet 's gravitational field.


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These maps depict topography, or surface features. In these images, white and red features are highest in relative elevation, while green and blue areas are lowest. These images were made possible by data from the Mars Orbiter Laser Altimeter (MOLA), which bounced a laser off the surface of the planet and calculated the distance traveled by the beam of light.

Gravitational Field

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These maps portray observed data describing Mars's gravitational field. Seen here, white and red areas depict regions with the strongest gravitational force, while green and blue areas are the weakest. These images were generated by data reported by the Radio Science Experiment.

Looking at the Moho--A Map of the Crust

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These images portray observed data describing Mars's gravitational field.

These maps are similar to the first two, but with an important distinction: the data used to create it are based on inferences generated by combining the topographical and gravitational maps. In these images, blues indicate thin areas of crust, while red and white indicate thicker areas. This synthetic visualization clearly shows how comparatively thin the crust is in the Northern Hemisphere versus the Southern Hemisphere. The relationship of a planet 's crust to topography and gravity is complicated, but it 's ultimately related to a geological region called the "moho", named for Croatian seismologist Andrija Mohorovicic, who first described it. The moho is the region where the crust and mantle meet. By determining the thickness of the crust and generating a map of the moho, scientists are developing a better understanding about the interior structure of Mars. As described in these images, the moho map does not show the same sharp resolution of features as do the surface maps. This is primarily due to the fact that it 's derived from other data, not a map created by direct observation. The slight undulations that appear in its surface are actually just digital artifacts of the synthetic process that enabled the data set to be developed. It quantifies the crustal thickness, but its main purpose is to work on the issue of why the thickness differences are so extreme. Project researchers say this adds evidence to the theory that there may have been an unusual type of convective cooling on Mars when it was a younger planet. Using this new sub-surface, interior view, scientists have a window into Mars 's geologic past and the forces that shaped the surface we see today.

An Asymmetrical Planet - The Martian Mantle

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Measurements of Mars 's gravity field, topography, and the subsequently derived crustal map show the Southern Hemisphere to be significantly thicker than the North. In this visualization, we show a cutaway of the planet's skin, with surface features and crustal thickness displayed in relative sizes to each other. (The features have been exaggerated by a factor of twenty-five times to make them stand out.) Notice how the crust on the right side of the cross section appears significantly thicker than the crust on the left. As discussed in the next section, the dramatic differences from one side of the planet are likely explained by a fascinating phase in the early states of Martian development.

Subsurface Water Channels - Ancient Clues to a Wetter Martian Surface

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Evidence suggests that rapid heat flow in the Northern Hemisphere produced a wide lowland area there, encouraging the formation of channels, which could have sluiced water resources into a large basin, even an early ocean. These images show a network of channels draining from the giant Valles Marineris into the wide, flat area of the north. Other areas that show similar signs are The Chryse and Kasei Valles outflow regions. These channels yawn nearly 200 kilometers wide and run more than 1650 kilometers long.

A Working Theory about an Unusual Radiator

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The research being released this week about the Martian crust is intended as a tool for experts to work on questions about the history of the planet. The dramatic asymmetry in structure suggests that the planet did not cool evenly for reasons that are still somewhat unclear. The low-lying terrain of the Northern Hemisphere suggests that Mars might have released more heat from the north than the south. In other words, the north might have taken longer to cool. In much the way that pudding forms lumps if it cools quickly, the south is believed to be higher and lumpier than the north precisely because it cooled so much faster. With much of the planet 's heat being radiated in the North, the terrain there formed a smoother, lower average topography, and therefore a thinner crust.

This puzzling evidence about early Martian convection adds to the observational signs that Mars may have once had more Earth-like properties, including the possibility of a northern ocean. Liquid water and other gasses trapped beneath the Martian surface could have propagated through rocks and fissures as a result of this rapid heat transfer while the planet cooled. With a lower Northern Hemisphere, water would have migrated in that direction, resulting in corresponding outflow channels and networks valleys. According to the gravity field measurements features interpreted to be channels lay buried beneath the plains stretching away from the solar system 's largest valley called Valles Marineris, as well as Mars's immense Chryse and Kasei Valles outflow regions. These now covered channels may represent the means for filling an early ocean.
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Mapping Martian Gravity - Ingenuity and Precision Yield Exciting Results

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Determining the gravitational map of Mars is not unlike trying to map weather patterns on Earth by standing on the Moon and using a telescope to watch a milkweed blossom dance on a spring breeze. Yet it was essentially just such a cause and effect observation that helped experts draw the gravitational chart of our planetary neighbor. Researchers developed this map of the planet's gravity with the simply named Radio Science Experiment. It worked like this: slight variations in the expected time required for radio signals to travel between Earth and Mars pointed to inconsistencies in the planet 's gravitational field. Those inconsistencies were deduced to be what caused the Surveyor 's orbit to "wiggle" as it wheeled around the Red Planet, thus causing the transmission time variations. If we consider gravity to be a descriptive property of mass, we can see how contours and ripples in the planet 's crust directly affect the path of the spacecraft by causing changes to the Martian gravitational field. It is important to emphasize here that it 's variation in the crust, not surface topography, which affects the gravitational field. As shown in this visualization, variations in the crust have a direct relationship to the orbital track. The calculations necessary to complete this task were significant, requiring that a daunting cluster of peripheral factors be taken into account. Some of these include movement of the planets through the solar system, transmission anomalies, and the sheer fact that the measurements were being taken from more than half a billion kilometers away by an instrument only the size of a small car.

A Tape Measure Made of Light - Mars Orbiter Laser Altimeter (MOLA)

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The Mars Orbiter Laser Altimeter (MOLA) has fired a precise beam of light at the planet it 's circling more than 300 million times. By measuring the two-way travel time of that laser as it flashes down to the surface and then as it 's reflected back up to the orbiter, a precise altitude scheme can be determined and compiled, which then can be converted into a detailed topographical map. As MOLA has refined its data sets with continuing collection of topographic data, research continues into the study of Martian volcanoes, lithospheric features, and possible routes where water might have moved across the surface.

To keep track of the MOLA laser's progress as it continues to rack up measurements, click here.

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This multimedia project is the work of a dedicated team of researchers, animators, and media specialists. A companion video to this web site is available from NASA-TV. Below are a list of agencies, departments, and researchers who provided expertise and data for this production:

Please give credit for these images to:
NASA - Goddard Space Flight Center
Scientific Visualization Studio
Television Production NASA-TV/GSFC
The MOLA Instrument and Science Team

Content Preparation and Project Production: Michael Starobin

Last Revised: February 4, 2019 at 06:02 PM EST