New gravity map suggests Mars has a porous crust

September 13, 2017 by Elizabeth Zubritsky
A new map of the thickness of Mars' crust shows less variation between thicker regions (red) and thinner regions (blue), compared to earlier mapping. This view is centered on Valles Marineris, with the Tharsis Montes near the terminator to its west. The map is based on modeling of the Red Planet's gravity field by scientists at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The team found that globally Mars' crust is less dense, on average, than previously thought, which implies smaller variations in crustal thickness. Credit: NASA/Goddard/UMBC/MIT/E. Mazarico

NASA scientists have found evidence that Mars' crust is not as dense as previously thought, a clue that could help researchers better understand the Red Planet's interior structure and evolution.

A lower density likely means that at least part of Mars' crust is relatively porous. At this point, however, the team cannot rule out the possibility of a different mineral composition or perhaps a thinner crust.

"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 Sander Goossens of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Goossens is the lead author of a Geophysical Research Letters paper describing the work.

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). That's comparable to the average density of the . Typically, Mars' crust has been considered at least as dense as Earth's , which is about 2,900 kilograms per meter cubed (about 181 pounds per cubic foot).

The new value is derived from Mars' , a global model that can be extracted from satellite tracking data using sophisticated mathematical tools. The gravity field for Earth is extremely detailed, because the data sets have very high resolution. Recent studies of the Moon by NASA's Gravity Recovery and Interior Laboratory, or GRAIL, 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. As a result, 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 Greg Neumann, a co-author on the paper. "We also need to know how the rocks have been reworked over time."

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. A constraint compensates for the fact that even the best data sets can't capture every last detail. Instead of taking the standard approach, known to those in the field as the Kaula constraint, 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 ," said Goddard geophysicist Terence Sabaka, the second author on the paper.

Before taking on Mars, the researchers tested their approach by applying it to the field that was in use before the GRAIL mission. 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).

From the new model, the team generated global maps of the crust's and thickness. These maps show the kinds of variations the researchers expect, such as denser beneath Mars' giant volcanoes.

The researchers note 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.

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betterexists
1 / 5 (8) Sep 13, 2017
Why are we so much worried about Mars?
Have we worried about OUR HOUSES At All?
Do we have a Roller Coaster that Rises from FLOOR Towards the Roof exposing the stored stuff ?
Jeffhans1
5 / 5 (11) Sep 13, 2017
Why are we so much worried about Mars?
Have we worried about OUR HOUSES At All?
Do we have a Roller Coaster that Rises from FLOOR Towards the Roof exposing the stored stuff ?

If everyone had the same attitude as you, we would still be living in trees, afraid of the dark.
Mark Thomas
5 / 5 (4) Sep 13, 2017
I would have guessed the lower crust density might be more due to a greater percentage of lower density materials, such as water ice, than porosity. Although Martian gravity is weaker than Earth's (38%), it would still impose limits on porosity as one goes deeper into the crust.
krzychu01230
1 / 5 (2) Sep 14, 2017
Gravity based estimation of density can be not quite correct because 'constant' G is mass dependent and mass is energetic variable thus G is also variable. This concept can solve some problem with estimated mass/density of comets as well as problem with prehistoric megafauna.
Shootist
3 / 5 (2) Sep 14, 2017
I would have guessed the lower crust density might be more due to a greater percentage of lower density materials, such as water ice, than porosity. Although Martian gravity is weaker than Earth's (38%), it would still impose limits on porosity as one goes deeper into the crust.


Whacked by so many bolides during the LHB the crust of Mars is essentially a pile of loosely packed rubble. The Moon is similar (see GRAIL results).
Mark Thomas
5 / 5 (4) Sep 14, 2017
Whacked by so many bolides during the LHB the crust of Mars is essentially a pile of loosely packed rubble.


The LHB certainly had an effect on Mars, but the precise extent is not yet clear. The fact that there is still relatively strong crustal magnetism in the Southern Hemisphere strongly suggests the Northern Hemisphere took most of the beating that erased a lot of magnetism. For example, crustal magnetism in Utopia Planitia is essentially wiped out.

https://en.wikipe..._MGS.png

Regarding density, large parts of Mars are thought to have buried ice. For example, Utopia Planitia is thought to have as much water as buried ice as Lake Superior.

https://www.jpl.n...ure=6680

There are still so many possibilities I think it is fair to conclude more investigation is needed, preferably in person.

http://www.scienc...-or-bang
Shootist
5 / 5 (1) Sep 16, 2017
Great points!

The LHB cratering rates between Mars and the Moon are statistically identical and were greatly under-estimated until recently.

https://gsa.confe...4126.htm
http://onlinelibr...515/full]http://onlinelibr...515/full[/url]

The remnant magnetism seen in the southern highlands appears to represent crustal spreading in the presence of a reversing dynamo. Yet the dynamo should have ended with the impacts that formed Utopia and Hellas. That portion of Martian crust didn't experience a large, >1000 km, basin-forming event.

http://www.pnas.o...970.long
http://www.igpp.u...u247.pdf
http://onlinelibr...515/full]http://onlinelibr...515/full[/url]

The point of a rubblized Martian crust is that it would provide the space for harboring a planetary ocean of water.

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