Mercury’s Crust Mystery

Researchers from the University of Arizona are using advanced mathematical formulas to more accurately measure Mercury’s crust thickness. Mercury’s crust was thought to be around 35 Kilometres thick but this new data put the figure more around the 25 Kilometre mark.

So why do scientist care about the thickness of the crust on a planet that’s uninhabitable, for now anyway? Well, there is a mystery to be solved and it all starts with Mercury’s core. Earth’s core accounts for around 15% of its volume but Mercury’s takes up a whopping 60% of the planet’s volume!

“Of the terrestrial planets, Mercury has the biggest core relative to its size,” the lead researcher says. “Maybe it formed closer to a normal planet and maybe a lot of the crust and mantle got stripped away by giant impacts. Another idea is that maybe, when you’re forming so close to the sun, the solar winds blow away a lot of the rock and you get a large core size very early on. There’s not an answer that everyone agrees to yet.”

The new study is already shedding light on the mystery, especially regarding the rocks in Mercury’s crust. When the planets and Earth’s moon formed, their crusts were born from their mantles, the layer between a planet’s core and crust that oozes and flows over the course of millions of years. The volume of a planet’s crust represents the percentage of the mantle that was turned into rocks.

Our moon is about the closest object in our solar system size wise to Mercury and the amount of mantle that turned into crust was about 7%. Mercury’s mantle to crust conversion rate is much higher at around 11%. “The two bodies formed their crusts in very different ways, so it wasn’t necessarily alarming that they didn’t have the exact same percentage of rocks in their crust,”

Mercury may look boring to the human eye, different minerals appear in a rainbow of colors in this image from NASA’s MESSENGER spacecraft. (Image credit: NASA/Johns Hopkins University APL/Carnegie Institution of Washington)

The moon’s crust formed when less dense minerals floated to the surface of the liquid rock that became the mantle. The moon’s minerals cooled and hardened into a “floatation crust’ where mercury’s volcanic eruptions caused its “magmatic crust”. This new research solves the apparent discrepancy in the amount of rock that formed between these two similar sized astrological bodies by showing that both Mercury & the moon have roughly 7%.

Researchers used the data from Messenger to create a topographic map but until now a density map had not been made. “We know what minerals usually form rocks, and we know what elements each of these minerals contain. We can intelligently divide all the chemical abundances into a list of minerals. We know the densities of each of these minerals. We add them all up, and we get a map of density.”

Messenger collected much more data on the northern hemisphere than the southern, and Sori predicts the average density of the planet’s surface will change when density data is collected over the entire planet. He already sees the need for a follow-up study in the future.

The next mission to Mercury will arrive at the planet in 2025.

Source: University of Arizona

This article was featured in Issue #1 of the Into the Void Science Magazine. Read the whole magazine for free by clicking on the image below

Into The Void Science Magazine – Issue #1

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