Gravity on Mars varies significantly. The red zone is an area of high gravity around the province of Tharsis, surrounded by an unexpected region of low gravity that needs to be explained.
Sediments deposited during the time when Mars had a large ocean cover structures whose high densities have been detected in the process of gravity mapping the planet. However, their nature and cause remain a mystery. The same mapping process suggests that the largest volcano in the Solar System, Olympus Mons, may grow even larger as a result of the forces
Given the large number of satellites now orbiting Mars, we can detect local variations in the red planet’s gravity as they pass by based on subtle changes in their speeds. Dr. Bart Root of Delft University of Technology presented the results of an analysis of these movements at the Europlanet Science Congress in Berlin last week.
Root highlighted the identification of hidden structures on the northern polar plains where water flowed when Mars had it.
“These dense structures could be volcanic in origin or compacted material from ancient impacts. There are about 20 features of various sizes that we have identified dotted around the area around the Arctic ice cap – one of which resembles the shape of a dog,” Root said in a statement.
Gravity on Mars varies significantly
“There doesn’t seem to be any sign of them on the surface. However, through gravity data, we have a tantalizing glimpse into the older history of the Northern Hemisphere
The mysterious structures are substantially denser than the locations around them, with a difference of about 300-400 kilograms per cubic meter. This places them 10-13 percent above the average density of the Martian crust and only slightly below the density of the mantle.
Any of Root’s possible explanations would change the way we see Mars. “If these structures are interpreted as impact craters, this would suggest an older age of Mars’ northern hemisphere crust than currently thought.”
The other major feature presented by Root comes from the Tharsis Rise, the part of Mars that contrasts most with the polar lowlands. Here, gigantic mountains that dwarf anything on Earth tower over the surrounding terrain, including Olympus Mons, the tallest of them all.
The Tharsis area presents an enigma in the form of a weak gravity region that surrounds it. This must be the result of a wide area of low density, but the volcanoes themselves are the opposite.
Hidden structures on the arctic plains
Root and his colleagues propose that – more than 1,000 kilometers deep, or about a third of the way to the center – there is a low-density pouch with a diameter of 1,600 kilometers. The area identified by Root is only slightly less dense than what surrounds it – by about 60 kilograms per cubic meter – representing a much smaller deviation than the polar structures, but its surface is much larger and is probably 350 kilometers thick .
He attributes this to a giant slab of lava rising up and leaving behind a relative void. If so, this plume could not only have created volcanoes twice as tall as any volcano on Earth, but continues to raise them, he writes.
Volcanologists hardly dared to dream that Mars was still volcanically active, but there are growing indications that it could be true.
“NASA’s InSight mission has given us crucial new information about the hard outer layer of Mars. This means we need to rethink how we understand the support for Olympus Mons and its surroundings,” said Root. “This shows that Mars may still have active movements in its interior that are affecting and possibly creating new volcanic features on the surface.”
