A new map of Mars’ gravity is now providing new insights into the hidden interior of the Red Planet. The mapping was made with three of NASA’s spacecrafts, and is the most detailed map to date.
Antonio Genova, of the Massachusetts Institute of Technology (MIT) and the lead author of the study published in the journal, Icarus, said in a statement:
“Gravity maps allow us to see inside a planet, just as a doctor uses an X-ray to see inside a patient.
“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.”
According to NASA, the enhanced resolution of the new gravity map gives a new explanation on how some features formed across the boundary that divides the relatively smooth northern lowlands from heavily cratered southern highlands.
“By analyzing tides within the Martian crust and mantle, the team was also able to confirm that Mars has a liquid outer core of molten rock; these tides are caused by the gravitational pull of the sun and the two moons of Mars.
“The team had also observed how Mars’ gravity had changed over 11 years, which is the period of an entire cycle of solar activity. The team inferred the massive amount of carbon dioxide that freezes out of the atmosphere onto a Martian polar ice cap when it experiences winter, NASA added.
“It was also observed by the team, how the mass moves between the South Pole and the North Pole with the change of season in each hemisphere.”
The map was created from range tracking and Doppler data that was 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).
Watch this video from NASA Goddard about the gravity map:
As with all planets, Mars is uneven. This is what causes the gravitational pull to change, as spacecraft orbit around it. “For example, the pull will be a bit stronger over a mountain, and slightly weaker over a canyon.”
These small differences in Mars’ gravity alter the trajectory of the NASA spacecraft orbiting the planet; in turn this alters the signal that is being sent from the spacecraft to the Deep Space Network. It was these slight variations in the orbital data that were used to build the map of Mars’ gravity field.
Sixteen years of data that were continuously collected in orbit around Mars were used in the making of the map. However, it had taken two years of analysis and computer modeling to complete it. This was due to the fact that orbital changes from uneven gravity are quite small, with other forces also contributing to the changes. These other forces include “the force of sunlight on the spacecraft’s solar panels and drag from the Red Planet’s thin upper atmosphere.”
Genova explained, saying that:
“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).
“The better resolution of the new map helps interpret how the crust of the planet changed over Mars’ history in many regions.”
For example, an area of lower gravity between Acidalia Planitia and Tempe Terra was interpreted before 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 Martian climate was wetter than it is today, according to NASA.
The map indicates that this low gravity irregularity is definitely larger, and it follows the boundary between the highlands and the lowlands. The researchers believe “that the system of gravity troughs is unlikely to be only due to buried channels because in places the region is elevated above the surrounding plains.”
The new gravity map demonstrates that a certain number of these features run perpendicular to the local topography slope, against what once would have been the natural downhill flow of water.
However, there is another explanation, and that is this anomaly may be a consequence of a “flexure or bending of the lithosphere” (the strong, outermost layer of the planet), owing to the formation of the Tharsis region.
Tharsis is a volcanic plateau on Mars that is thousands of miles across, and has the largest volcanoes in the solar system. The theory is as the Tharsis volcanoes grew, the nearby lithosphere buckled under their enormous weight.
The new gravity field also allowed the team to confirm indications from previous gravity solutions that Mars has a liquid outer core of molten rock. The new gravity solution improved the measurement of the Martian tides, which will be used by geophysicists to improve the model of Mars’ interior, NASA wrote.
Previous measurements of Mars’ gravity have been conducted using the MGS and ODY missions to monitor the polar ice caps. However, this is the first time MRO data has been used to continue monitoring their mass.
The team has determined that while one hemisphere experiences winter, approximately 3 to 4 trillion tons of carbon dioxide freezes out of the atmosphere onto the northern and southern polar caps, respectively, NASA added.
This is around 12 to 16 percent of the mass of the whole Martian atmosphere. It was NASA’s Viking missions that first observed this immense seasonal precipitation of carbon dioxide. The new observation has now confirmed the numerical predictions from the Mars Global Reference Atmospheric Model 2010.