These colourful maps of Mars are the most accurate depiction of how gravity varies around the Red Planet. Created by measuring subtle variations in the gravitational field experienced by NASA spacecraft as they zip past the planet, the images allow us to understand what lurks inside better than ever. The map was created using data gathered from Mars Global Surveyor (MGS), Mars Odyssey (ODY) and the Mars Reconnaissance Orbiter (MRO). Subtle differences in the gravitational field cause minute changes in the trajectory of the spacecraft. Those differences can be measured, geotagged, compiled and over time used to create these maps.
Using three satellites provides a means of verification, but the process was a slow one: The maps are made up of almost 16 years worth of data. And because the variations in measurement are so small, the NASA-MIT team that processed the data had to carefully scrutinise and process it — which took two years itself.
A map of Martian gravity looking down at the North Pile (left) and South Pole (right). (Image by MIT/UMBC-CRESST/GSFC)
The scientists are already using the maps to get a better understanding of the planet. For instance, the data can be used to understand gravitational anomalies over the surface of the planet — some as small as 100km across — as well as allowing the team to calculate the thickness of the planet's crust with more accuracy than before. In fact they can measure the crust thickness with a resolution of 121km, helping them understand what causes the variation in gravity as well as confirming previous results that found Mars to have a liquid outer core of molten rock.
The variations in gravitational field over time have also allowed the team to predict that three to four trillion tonnes of carbon dioxide freezes out of the atmosphere onto the northern and southern polar caps during a Martian winter. That's about 12 to 16 per cent of the mass of the entire atmosphere.
Top: A Martian gravity map showing high-gravity areas in white and low-gravity areas in blue. (Image by MIT/UMBC-CRESST/GSFC)