NASA researchers have found evidence that Mars’ crust is not as dense as previously thought.
This likely means that at least part of Mars’ crust is relatively porous – but at this point, the team can’t rule out the possibility of a different mineral composition or perhaps a thinner crust.
The new findings could help researchers understand the Red Planet’s interior structure and evolution.
A new map of the thickness of Mars’ crust shows less variation between thicker regions (red) and thinner regions (blue), compared to earlier maps. This view is centered on Valles Marineris. The NASA team found that globally Mars’ crust is less dense, on average, than previously thought, which implies smaller variations in crustal thickness
‘The crust is the end-result of everything that happened during a planet’s history, so a lower density could have important implications about Mars’ formation and evolution,’ said Dr Sander Goossens of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of a Geophysical Research Letters paper describing the work.
To conduct the study, the researchers mapped the density of the Martian crust, estimating the average density is 2,582 kilograms per meter cubed (about 161 pounds per cubic foot).
This is comparable to the average density of the lunar crust, but typically, Mars’ crust has been considered at least as dense as Earth’s oceanic crust, which is about 2,900 kilograms per meter cubed (181 pounds per cubic foot).
The new density value was derived from Mars’ gravity field, a global model that can be extracted from satellite tracking data using mathematical tools.
The gravity field for Earth is extremely detailed, because the data sets have very high resolution, and recent studies of the moon by NASA’s Gravity Recovery and Interior Laboratory mission also yielded a precise gravity map.
The data sets for Mars don’t have as much resolution, so it’s more difficult to pin down the density of the crust from current gravity maps, which is why previous estimates relied more heavily on studies of the composition of Mars’ soil and rocks.
‘As this story comes together, we’re coming to the conclusion that it’s not enough just to know the composition of the rocks,’ said Goddard planetary geologist Dr Greg Neumann, a co-author on the paper.
‘We also need to know how the rocks have been reworked over time.’
Dr Goossens and colleagues started with the same data used for an existing gravity model but put a new twist on it by coming up with a different constraint and applying it to obtain the new solution.
Using their new model, the team generated global maps of the crust’s density and thickness, which showed the kinds of variations the researchers expected – such as denser crust beneath Mars’ giant volcanoes. Pictured is a 1700km-wide region of Mars, including Olympus Mons (upper left) and several other volcanoes of Mars’s Tharsis province
In this context, a constraint compensates for the fact that even the best data sets can’t capture every detail.
So, instead of taking the standard approach, the team created a constraint that considers the accurate measurements of Mars’ elevation changes, or topography.
‘With this approach, we were able to squeeze out more information about the gravity field from the existing data sets,’ said Goddard geophysicist Dr Terence Sabaka, the second author on the paper.
Before trying Mars, the researchers tested their approach by applying it to the gravity field that was in use before the GRAIL mission.
A mosaic of the Schiaparelli Hemisphere of Mars, showing the Schiaparelli Crater, circa 1980. New research has revealed that Mars’ crust is not as dense as previously thought. The findings could help researchers understand Mars’ interior structure and evolution
The resulting estimate for the density of the moon’s crust essentially matched the GRAIL result of 2,550 kilograms per meter cubed (about 159 pounds per cubic foot).
Using their new model, the team generated global maps of the crust’s density and thickness, which showed the kinds of variations the researchers expected – such as denser crust beneath Mars’ giant volcanoes.
The researchers say that NASA’s InSight mission — short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport — is expected to provide the kinds of measurements that could confirm their finding.
This Discovery Program mission, scheduled for launch in 2018, will place a geophysical lander on Mars to study its deep interior.