A team of scientists presented a new gravity map of Mars at the Europlanet Science Congress 2024. The map shows the presence of dense, large-scale structures beneath Mars’ long-vanished ocean and that mantle processes are affecting Olympus Mons, the largest volcano in the Solar System.
The new map and analysis includes data from multiple missions, including NASA’s InSIGHT (Interior Exploration Using Seismic, Geodetic, and Heat Transport) mission. They also use data from small deviations in satellites as they orbit Mars.
The paper “Mars’ Global Gravity Field Reveals an Active Interior” will be published in an upcoming issue of JGR: Planets. The lead author is Bart Root of Delft University of Technology. Some of the results go against an important concept in geology.
Geologists work with a concept called flexural isostasy. It describes how the solid outer layer of a planet responds to large-scale loading and unloading. The layer is called the lithosphere and consists of the crust and the uppermost part of the mantle.
When something heavy loads the lithosphere, it responds by sinking. On Earth, Greenland is a good example of this, where the massive ice sheet exerts downward pressure on it. As its ice sheets melt due to global warming, Greenland will grow.
This downward bending often causes an uplift in the surrounding areas, although the effect is slight. The more massive the load, the more pronounced the downward bending, although it also depends on the strength and elasticity of the lithosphere. Flexural isostasy is a critical idea for understanding glacial retreat, mountain formation, and sedimentary basin formation.
The authors of the new paper say scientists need to rethink how flexural isostasy works on Mars. This is due to Olympus Mons, the largest volcano in the Solar System, and the entire volcanic region called Tharsis Rise, or Tharsis Montes. Tharsis Montes is a large volcanic region that holds three other large shield volcanoes: Arsia Mons, Pavonis Mons, and Ascraeus Mons.
Flexural isostasy states that this massive region must force the surface of the planet down. But the opposite is true. Tharsis Montes is much higher than the rest of the Martian surface. NASA’s InSIGHT lander also told scientists a lot about Mars’ gravity, and together, it’s forcing researchers to reconsider how it all works on Mars.
“This means that we need to rethink how we understand support for large volcanoes and their surroundings,” the authors write. “The gravity signal of its surface fits well with a model that considers the planet as a thin shell.”
The research shows that active processes in the Martian mantle are driving Tharsis Montes up. “There appears to be a large mass (something light) deep in the mantle of Mars, which may rise from the mantle,” the authors write. “This shows that Mars may still have active movements going on inside it, creating new volcanic things on the surface.”
The researchers found an underground mass about 1,750 kilometers wide and at a depth of 1,100 kilometers. They suspect it is a mantle plume rising beneath Tharsis Montes and strong enough to oppose downward pressure from the entire mass.
“This suggests that a plume head is currently flowing upward into the lithosphere to generate active volcanism in the geological future,” the authors write in their paper.
There is debate about how volcanically active Mars is. Although there are no active volcanic features on the planet, research indicates that the Tharsis region has re-emerged in the recent geological past within the last tens of millions of years.
If there is a mantle plume beneath Tharsis Montes, could it eventually reach the surface? This is purely speculative, and more research is needed to confirm these findings.
The researchers also found other gravitational anomalies. They found mysterious and dense structures beneath the northern polar fields of Mars. They are buried under a thick, smooth layer of sediment that was likely deposited on an ancient seabed.
The anomalies are approximately 300-400 kg/m3 denser than their surroundings. Earth’s Moon has gravitational anomalies associated with giant impact basins. Scientists think that the impactors that created the basins were denser than the Moon and their mass became part of the Moon.
Impact basins on Mars also show gravity anomalies. However, the anomalies in the northern hemisphere of Mars do not show their traces on the surface.
“These dense structures may be of volcanic origin or may be compacted material due to ancient impacts. There are about 20 features of various sizes that we have identified dotted around the area around the north polar cap – one of which it resembles the shape of a dog,” said Dr. Root.
“There appears to be no trace of them on the surface. However, through the gravity data, we have a fascinating glimpse into the oldest history of the northern hemisphere of Mars.”
The only way to understand these mysterious structures and the gravity of Mars in general is with more data. Root and his colleagues are proponents of a mission that could collect the necessary data.
It’s called the Martian Quantum Gravity (MaQuls) mission. MaQuls would be based on the same technology used in the GRAIL (Gravity Recovery and Interior Laboratory) and GRACE (Gravity Recovery and Climate Experiment) missions, which mapped the gravity of the Moon and Earth, respectively. MaQuls would feature two satellites tracking each other and connected by an optical link.
“Observations with MaQuIs would enable us to better explore beneath the surface of Mars. This would help us discover more about these mysterious hidden features and study the ongoing convection of the mantle, as well as understand dynamic surface processes such as seasonal atmospheric changes and the detection of water reservoirs,” said Dr. Lisa Wörner of DLR, who presented at the MaQuIs mission at EPSC2024 this week.
This article was originally published by Universe Today. Read the original article.