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Gravity map gives glimpse inside Mars

A Martian gravity map showing the Tharsis volcanoes and surrounding flexure. The white areas in the center are higher-gravity regions produced by the massive Tharsis volcanoes, and the surrounding blue areas are lower-gravity regions that may be cracks in the crust (lithosphere). Image Credit: MIT/UMBC-CRESST/GSFC

A Martian gravity map showing the Tharsis volcanoes and surrounding flexure. The white areas in the center are higher-gravity regions produced by the massive Tharsis volcanoes, and the surrounding blue areas are lower-gravity regions that may be cracks in the crust (lithosphere). Image Credit: MIT/UMBC-CRESST/GSFC

A team of scientists using data gathered by three NASA spacecraft have created the most detailed gravity map of Mars to date, providing scientists with a revealing glimpse of the Red Planet’s hidden interior. The researchers published their findings online March 5 in the journal Icarus.

“Gravity maps allow us to see inside a planet, just as a doctor uses an X-ray to see inside a patient,” said Antonio Genova of the Massachusetts Institute of Technology (MIT), Cambridge. “The new gravity map will be helpful for future Mars exploration, because better knowledge of the planet’s gravity anomalies helps mission controllers insert spacecraft more precisely into orbit about Mars. Furthermore, the improved resolution of our gravity map will help us understand the still-mysterious formation of specific regions of the planet.”

The improved gravity map suggests a new explanation for how some geological features formed across the boundary that divides the fairly smooth northern lowlands of Mars from the heavily cratered southern highlands. The team also confirmed that Mars has a liquid outer core of molten rock by analyzing tides in the Martian crust and mantle caused by the gravitational pull of the Sun and the two moons of Mars. The scientists were also able to infer the massive amount of carbon dioxide that freezes out of the Martian atmosphere and onto a polar icecap by observing the planet’s gravity for an entire 11-year period of solar activity. The team also observed how the mass of carbon dioxide moves between the north pole and south pole with the change of season in each hemisphere.

Newly detailed mapping of local variations in Mars' gravitational pull on orbiters (center), combined with topographical mapping of the planet's mountains and valleys (left), yields the best-yet mapping of Mars' crustal thickness (right).Image Credit: NASA/GSFC/Scientific Visualization Studio

Newly detailed mapping of local variations in Mars’ gravitational pull on orbiters (center), combined with topographical mapping of the planet’s mountains and valleys (left), yields the best-yet mapping of Mars’ crustal thickness (right). Image Credit: NASA/GSFC/Scientific Visualization Studio

The map was generated using Doppler and range tracking data collected by NASA’s Deep Space Network (DSN) from three spacecraft: Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). Mars is lumpy, which causes the gravitational pull on spacecraft in orbit around it to change. These slight changes in gravity affect the trajectory of the spacecraft, which in turn alters the signal being sent from the spacecraft to the Deep Space Network. These small fluctuations were used to map Mars’s gravity field.

The gravity map was created using about 16 years of data collected in orbit the map. In order to refine the map, factors other than gravity that could affect the motion of the spacecraft, such as the force of sunlight on the spacecraft’s solar panels, and drag from the thin upper atmosphere of Mars, had to be carefully accounted for. Two years of computer modeling and data analysis were required to remove the motion not caused by gravity.

Video courtesy of NASA

 

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Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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