Scientists believe Mars was much more similar to Earth in the distant past, not the dried-up 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 seismometer on the lander, researchers from Rice University have peeled back the layers below 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 emanating through the planet during “marsquakes” reveal aspects of the planet’s internal structure. On Earth, we have much more powerful seismic activity as a consequence of the active tectonic plates, and there are seismic sensors spread across the globe. On Mars, the rumbling is much more subtle, and there’s just one seismometer on the entire planet. Still, study co-authors Sizhuang Deng and Alan Levander identified three distinct transitions inside Mars.
The first transition zone starts a mere 22 miles (35 kilometers) beneath the lander, dividing the crust from the mantle. That’s surprisingly close to Earth’s crust transition, which is an average of 25 miles (40 kilometers) below your feet. The second zone is a transition between the upper mantle and lower mantle, which happens at a depth of 690-727 miles (1,110-1,170 kilometers). Above this cutoff, magnesium iron silicates form olivine. Below the transition, they are further compressed into a mineral called wadsleyite. Gathering data on the olivine-wadsleyite boundary is key to developing accurate thermal models of Mars.
The final boundary within Mars separates the lower mantle from the iron-rich core of the planet. It’s about 945-994 miles (1,520-1,600 kilometers) underground. Here, scientists are interested in what this boundary can tell us about the earliest phases of planetary formation. Mars is an ideal target to study planetary formation for several reasons, not least of which it’s relatively Earth-like and easy to explore. Venus, by comparison, will chew up anything we send into its super-dense corrosive atmosphere.
The upshot of the low tectonic activity is that Mars hasn’t changed much in the last few billion years. With its early history largely preserved, scientists are hopeful they can learn a great deal more about planetary formation and structure than they ever could on Earth.
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