New gravity map gives us a glimpse inside Mars

The most detailed map of Mars' gravity to date gives us unprecedented information about its interior.

"Gravity maps allow us to see inside a planet, just as a doctor uses an X-ray to see inside a patient," says Antonio Genova of the Massachusetts Institute of Technology and lead author of a paper published in the journal Icarus.

The map was created using data gathered by three NASA spacecraft and will assist in future exploration of the planet.

"Better knowledge of the planet's gravity anomalies helps mission controllers insert spacecraft more precisely into orbit about Mars," says Genova.

The improved resolution will help us understand the still-mysterious formation of specific regions of the planet, he says.

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A map of Martian gravity looking down on the North Pole (centre). White and red are areas of higher gravity; blue indicates areas of lower gravity. – MIT/UMBC-CRESST/GSFC

Already the map is shedding light on how some of the Red Planet's features formed across the boundary that divides the relatively smooth northern lowlands from heavily cratered southern highlands.

And analysis of tides in the Martian crust and mantle as it is pulled between the Sun and Mars' two moons confirm that the planet has a liquid outer core of molten rock.

The map also gives a picture as to how gravity has changed over 11 years  an entire cycle of solar activity. That shows a massive amount of carbon dioxide that freezes out of the atmosphere during winter. The map shows how the mass moves between the south pole and the north pole with the change of seasons.

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A map of Martian gravity looking down at the South Pole (centre). White and red are areas of higher gravity; blue indicates areas of lower gravity. – MIT/UMBC-CRESST/GSFC

The map uses data collected by NASA's Deep Space Network from three NASA spacecraft in orbit around Mars: Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO).

The map was built using slight fluctuations in data from the orbiting spacecraft as Mars' gravity changed their trajectory over about 16 years' orbit around Mars. But these fluctuations are tiny and it took two years to strip out other effects that can change the trajectory of the spacecraft, such as the force of sunlight on the spacecraft's solar panels and drag from the thin upper atmosphere. 

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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). – MIT/UMBC-CRESST/GSFC

"With this new map, we've been able to see gravity anomalies as small as about 100 kilometres across, and we've determined the crustal thickness of Mars with a resolution of around 120 kilometres," Genova says.

"The better resolution of the new map helps interpret how the crust of the planet changed over Mars' history in many regions."

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