NASA scientists have discovered additional evidence that Mars once underwent plate tectonics, slow movement of the planet’s crust, like the present-day Earth. A new map of Mars’ magnetic field made by the Mars Global Surveyor spacecraft reveals a world whose history was shaped by great crustal plates being pulled apart or smashed together.

Scientists first found evidence of plate tectonics on Mars in 1999. Those initial observations, also done with the Mars Global Surveyor’s magnetometer, covered only one region in the Southern Hemisphere. The data was taken while the spacecraft performed an aerobraking maneuver, and so came from differing heights above the crust.

This high resolution magnetic field map, the first of its kind, covers the entire surface of Mars. The new map is based on four years of data taken in a constant orbit. Each region on the surface has been sampled many times. “The more measurements we obtain, the more accuracy, and spatial resolution, we achieve," said Dr. Jack Connerney, co-investigator for the Mars Global Surveyor magnetic filed investigation at NASA’s Goddard Space Flight Center, Greenbelt, Md.

“This map lends support to and expands on the 1999 results,” said Dr. Norman Ness of the Bartol Research Institute at the University of Delaware, Newark. “Where the earlier data showed a “striping” of the magnetic field in one region, the new map finds striping elsewhere. More importantly, the new map shows evidence of features, transform faults, that are a “tell-tale” of plate tectonics on Earth.” Each stripe represents a magnetic field pointed in one direction­positive or negative­and the alternating stripes indicate a "flipping" of the direction of the magnetic field from one stripe to another.

Scientists see similar stripes in the crustal magnetic field on Earth. Stripes form whenever two plates are being pushed apart by molten rock coming up from the mantle, such as along the Mid-Atlantic Ridge. As the plate spreads and cools, it becomes magnetized in the direction of the Earth’s strong global field. Since Earth’s global field changes direction a few times every million years, on average, a flow that cools in one period will be magnetized in a different direction than a later flow. As the new crust is pushed out and away from the ridge, stripes of alternating magnetic fields aligned with the ridge axis develop. Transform faults, identified by “shifts” in the magnetic pattern, occur only in association with spreading centers.

To see this characteristic magnetic imprint on Mars indicates that it, too, had regions where new crust came up from the mantle and spread out across the surface. And when you have new crust coming up, you need old crust plunging back down­the exact mechanism for plate tectonics.

Connerney points out that plate tectonics provides a unifying framework to explain several Martian features. First, there is the magnetic pattern itself. Second, the Tharsis volcanoes lie along a straight line. These formations could have formed from the motion of a crustal plate over a fixed “hotspot” in the mantle below, just as the Hawaiian islands on Earth are thought to have formed. Third, the Valles Marineris, a large canyon six times as long as the Grand Canyon and eight times as deep, looks just like a rift formed on Earth by a plate being pulled apart. Even more, it is oriented just as one would expect from plate motions implied by the magnetic map.

“It’s certainly not an exhaustive geologic analysis,” said Dr. Mario Acuña, principal investigator for the Mars Global Surveyor magnetic filed investigation at Goddard Space Flight Center. “But plate tectonics does give us a consistent explanation of some of the most prominent features on Mars.”

Results were published in the Oct. 10 edition of the Proceedings of the National Academy of Science.

Other scientists working on the project included Dr. G. Kletetschka of the Catholic University of America, Washington, DC, and Goddard Space Flight Center; Dr. D.L. Mitchell and Dr. R.P. Lin of the University of California at Berkeley; and Dr. H. Reme of the Centre d’Etude Spatiale des Rayonnements in France. Dr. Acuña leads the international team that built and operates the Mars Global Surveyor magnetometers. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington.

For more information on the results, consult:

http://www.nasa.gov/vision/universe/solars...mgs_plates.html

I know barely that the Earth magnetic field is caused by the friction of tectonic plate movement. Otherwise, the Mars has at all no tectonic plate movement unless in some aisle sites such as the south of Gusev's crater where presents stronger magnetic field.

Rodolfo

I believe that the Earth's magnetic field is induced by the constant spinning of molten iron inside the Earth's core. When iron is molten, it more easily aligns to the magnetic force, and so when it first oozes out of the Earth, it will be magnetized. As it cools and solidifies, it will retain this magnetic alignment, which can then be measured billions of years later.

I also recall that if you were to randomly pound on any magnetized substance long enough, you would misalign the atoms, causing the substance to demagnetize. Conversely, if you were to pound on a magnetizable substance in the right way long enough, it would become magnetized.

What I can't remember is why spinning iron induces magnetism at all, but accoriding to wikipedia.org, this is 'dynamo theory', which states that when certain substances (iron and nickel for the Earth, I guess) spin, they reinforce pre-existing magnetic fields, which creates a self-sustaining magnetic field. I'm not sure where the original magnetic field came from, but I would personally guess that they spontaneously arise, as so many other things seem wont to do (the universe, and consciousness, for instance).

Please do not confuse the core magnetic field and its imprints on the surface!!!


The core magnetic field is a strong dipolar field (it has two poles, like the Earth magnetic field) which forms into the molten iron core of a planet, as mike explains. There are plenty of causes for the "dynamo" to start, like residual galactic magnetic field, or the Earth magnetic field in the case of a dynamo (the machine). This magnetic field is formed by electric currents into the conductive iron core. It happens that on Earth the magnetic field reverse its poles more or less regularly in time, so we can infer that this may also happen on other planets.

The magnetic imprints in the crust are much weaker, and are residues of the magnetic field the rock was submited to, when it solidified. The rock sill contains the magnetic direction, from iron bearing minerals. On Earth, in the oceanic crust, there are bands paralel to the formation line, alterning normal and reverse magnetic remnants. This was historically considered as the first hard evidence of the plate tectonic, when this theory emerged in the 1970'. But such simple banded patterns do not appear on continents, which evolution is much more complex.

finding banded patterns on Mars supports the idea that a plate tectonics existed in the past of Mars. But with my opinion, if there was plate tectonics on Mars, it was in a very early stage, when the planet was still very hot, forming a relatively flat basalt crust covering all the planet. But this stage was short (hundred million year?) and continents had no time to appear (one billion years was necessary to form the first continent on Earth). And all the features of this epoch were further burried and destroyed by the intense cratering of the early solar system.

The Tharsis dome, vales marineris and volcanoes are expected to have formed much later, and so they cannot be the consequences of plate tectonics. But until now nobody really knows what formed the Tharsis dome and related features. If we assume that Mars has the same inner structure than Earth, it is clear that today the iron core is solidified from long ago, leading to a very different mantle heat movement and repartition than on Earth. Some beacons: recent measurements of Earth heat sources showed that the solidifying of the core yelds four more time heat than radioactivity, and this heating is located in the bottom of the mantle, like in a boiling water pan. On Mars only radioactivity heats the mantle, and this may result in a totally different mantle movement and structure than on Earth.

I've always wondered if the formation of the Tharsis dome was somehow related to the Hellas impact - they seem to be about opposite each other on the surface. Is there any basis for that?

A year ago, I have read a document about the theory of the formation of big Mons (Ascareus, Tharsis, Olympus and Pavoni) are the product of the big impact that caused the biggest crater of Mars: Hella. The Mars' moon: Deimos and Phobos are the result of this impact. These big mons are almost on the opposite side to Hella's Crater. For more information, read the following URL: The Scars of Mars

Rodolfo

Possible. Another example would be on Mercury: opposite the Caloris Basin (the largest crater on Mercury) there exists chaotic (jumbled) terrain which is thought to be caused by the focused shock of the impact.

--Bill