Scientists have used a rather ingenious method to measure gravity on Mars more precisely than ever before. Using small perturbations in the positions of orbiting spacecraft, they have been able to map out regions of high and low gravity on the surface, published in the journal Icarus.
To put the map together, scientists used data from the Mars Global Surveyor, Mars Odyssey, and the Mars Reconnaissance Orbiter. Mars is “lumpy,” with regions of high elevation like Olympus Mons (the highest mountain in the Solar System), and low elevation like Valles Marineris (the biggest canyon system). Thus, the spacecraft are pulled by varying amounts as they fly over different regions.
Although small, these changes affect the signals that the spacecraft send back to Earth, which has allowed scientists to monitor how they are being shifted by the Martian gravity. Sixteen years of data were used in total to piece it all together, with two years of computer modeling required to eliminate other reasons for fluctuations, including solar wind.
The map allows gravitational anomalies as small as 100 kilometers (62 miles) to be seen. Comparing this map with a map of the Martian topography has also allowed scientists to refine the crustal thickness of the Red Planet, giving an upper limit of around 120 kilometers (75 miles).
"Gravity maps allow us to see inside a planet, just as a doctor uses an X-ray to see inside a patient," Antonio Genova of the Massachusetts Institute of Technology (MIT), lead author on the paper, said in a statement. In fact, the measure of the interior supports the theory that Mars has a liquid outer core of molten rock.
The team was also able to monitor the shifting amounts of carbon dioxide at the poles, with the large expanse of ice melting and refreezing during summer and winter. An astonishing 2.7 to 3.6 trillion tonnes (3 to 4 trillion tons) of carbon dioxide was found to shift between the poles, which is about 12 to 16 percent of the mass of the whole Martian atmosphere.
This research should also allow scientists to better prepare future missions to Mars, with spacecraft able to enter more precise orbits with the various anomalies known.