It is the most detailed map to date.
NASA has spent years sending spacecrafts and rovers to Mars to try to discover some of the planet’s mysteries, and it has definitely paid off! A new map of Mars’ gravity, or its "skeleton," made using three NASA spacecrafts, is the most detailed to date and it provides a revealing glimpse into the hidden interior of the Red Planet.
“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) said in a press release.
“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,” Genova continued.
The map was developed using 16 years worth of Doppler and range-tracking data collected from three NASA spacecraft in orbit around Mars. Like all rocky planets, Mars is lumpy, which causes the gravitational pull felt by spacecraft orbiting it to fluctuate. For example, the pull will be a bit stronger over a mountain, and slightly weaker over a canyon.
These slight differences in Mars’ gravity can change the trajectory of NASA's spacecraft, which alters the signal being sent from the spacecraft. It is these fluctuations in the orbital data that were used to build a map of the planet’s gravity field.
However, orbital changes from uneven gravity are extremely small, and other forces capable of disrupting the motion, such as the force of sunlight on the spacecraft's solar panels and drag from the Mars’ thin upper atmosphere, also had to be accounted for. It took two years of analysis and computer modeling to remove all motion not caused by gravity.
“With this new map, we've been able to see gravity anomalies as small as about 62 miles (100 kilometers) across, and we've determined the crustal thickness of Mars with a resolution of almost 75 miles (around 120 kilometers),” said Genova.
The new map has also provided a new explanation for how some features formed across the boundary that divides the smooth northern lowlands from the heavily cratered southern highlands. Previously, an area of lower gravity between the two was interpreted as a system of buried channels that delivered water and sediments from Mars’ southern highlands into the northern lowlands billions of years ago when the climate on the planet was wetter than it is today.
However, the new map revealed that this anomaly is likely caused by more than just the buried channels because the map shows that some of these features run perpendicular to the local topography, against what would have been the natural flow of water. An alternative explanation is the bending of the lithosphere, the outermost layer of the planet, due to the formation of the volcanic plateau Tharsis. As the Tharsis volcanoes grew, the surrounding lithosphere buckled under the weight.
The team also confirmed that Mars has a liquid outer core of molten rock. This was determined by analyzing tides in the crust and mantle caused by the gravitational pull of the sun and Mars’ two moons.
Finally, by observing how Mars’ gravity changed over 11 years — the length of a full solar cycle — the team found that massive amounts of carbon dioxide, 3 to 4 trillion tons (or 12 to 16 percent of the entire planet’s atmosphere), freeze out of the atmosphere and fall onto the planet's polar ice caps during each hemisphere’s winter.
The results were published online on March 5 in the journal Icarus.