Scientists believe that Mars was much more like Earth in the distant past, not the dried ball of dust it is today. Understanding Mars could help us better understand how planets form, and the NASA InSight mission has the tools to get us there. Using the lander seismometer, Rice University researchers peeled back the layers beneath the surface of the red planet like a giant, dusty onion.
The seismometer attached to InSight works the same as similar instruments on Earth – the vibrations created by the planet during “marsquakes” reveal aspects of the planet’s internal structure. On Earth, we have much more powerful seismic activity due to the active tectonic plates, and there are seismic sensors spread all over the world. On Mars, the clutter is much more subtle, and there is only one seismometer on the entire planet. Still, co-authors Sizhuang Deng and Alan Levander identified three distinct transitions within Mars.
The first transition zone begins only 35 kilometers below the lander, and divides the crust of the mantle. That is surprisingly close to the Earth’s short transition, which lies on average 25 miles (40 kilometers) below your feet. The second zone is a transition between the upper mantle and lower mantle, which occurs at a depth of 690-727 miles (1,110-1,170 kilometers). Above this cut, magnesium-iron silicates form olivine. During the transition, they are further compressed into a mineral called wadsleyite. Collecting data across the border of olivine wadsleyite is the key to developing accurate thermal models of Mars.
A SEIS seismic instrument (above) is the first seismometer ever deployed on another planet.
The definitive boundary within Mars separates the lower mantle from the iron core of the planet. It is about 945-994 miles (1,520-1,600 kilometers) underground. Here, scientists are interested in what this boundary can tell us about the early phases of planetary formation. Mars is an ideal target for studying planetary formation for a variety of reasons, not the least of which is relatively Earth-like and easy to explore. Venus, by comparison, will cherish everything we send in its super-dense corrosive atmosphere.
The result of the low tectonic activity is that Mars has not changed much in the last few billion years. With its early history largely preserved, scientists are hoping that they can learn much more about planetary formation and structure than they ever could on Earth.
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