December 1, 2023

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Mercury – the innermost planet in our solar system

Mercury – the innermost planet in our solar system

It is widely accepted that Mercury began contracting more than 3 billion years ago. But remarkably, this process seems to continue to this day, making the smallest planet in our solar system smaller and smaller.

Planetary scientists have long known that Mercury is no longer the same size as it was several billion years ago. Although Mercury is the planet closest to the Sun, the heat inside it has diminished over time as its internal heat gradually escapes. Because of this, Mercury is getting smaller and smaller. But the pressing question is whether the planet is still shrinking, and if so, how long will this continue? A new study published in Natural earth sciencesnow sheds new light on this issue.

Mercury’s past contraction is evident from numerous images and data collected by the MESSENGER spacecraft, which mapped the planet’s entire surface. These images reveal impressive steep cliffs, indicating that this small rocky planet was shrinking and its crust was undulating. This phenomenon is caused by the cooling of the planet, which made it smaller and compressed the Earth’s crust. The result is massive cliffs, some more than a kilometer high and hundreds of kilometers wide, that still characterize Mercury’s landscape.

More about MESSENGER’s mission
MESSENGER was launched in 2004 and arrived at Mercury in 2011. It was to conduct research there for a year. But MESSENGER ended up studying the planet for four years. During that period, the space probe revealed many secrets of the smallest planet in our solar system. For example, he determined the surface composition of Mercury and was able to confirm that water ice could be found at the poles. In 2015, time ran out and the space probe was ordered to drill into the surface of Mercury. There the probe created a new crater.

Meanwhile, we know that Mercury began contracting at least three billion years ago. Both models and scientific observations suggest that the planet’s radius may have shrunk by as much as 7 km. Since then, the planet’s contraction rate has likely slowed.

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Recent tectonic activity
Until now, there has been no evidence of recent tectonic activity on Mercury. But the research team has now changed that. Thus, the recently published study provides compelling evidence that Mercury not only contracted in the past, but continues to do so today.

The researchers came to this conclusion after looking at data collected by MESSENGER. Then they discovered small new landforms called grabins. These structures are structures that exist on top of larger, pre-existing compressional tectonic structures on the planet. Since these objects are relatively small and shallow, you wouldn’t expect them to last for hundreds of millions of years, let alone a billion years. This is because they will disappear quickly due to impacts on a geological time scale.

Cross section of Mercury’s crust. Photo: DA Rothery, CC BY

More about seizure
Graben are tectonic structures in the planet’s crust that form due to tectonic pressure and stretching of the crust. They are often associated with valleys or low-lying areas located between two parallel fault lines. Grains form when the Earth’s crust moves apart, causing part of the crust to subside and creating a relatively elongated crater.

Researchers suspect that many of the newly discovered cratons formed over the past 100 million years. The fact that so many scribbles are found on top of large compressional tectonic structures indicates that recent tectonic activity has occurred all around Mercury. This is strong evidence that the planet is still shrinking, and this process continues today.

“The discovery of this little hook happened by chance,” says researcher Benjamin Mann. “While I was doing my doctoral research, I unexpectedly came across some amazing structures. I then decided to analyze more than 25,000 individual images, which led to the discovery of hundreds of grapevines. The discovery of many of these structures is of great importance because it not only shows that Mercury was “This has important implications because it confirms that the global contraction of Mercury is still ongoing. It also raises questions about the chemical properties of the planet’s interior.”

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Similar terrain
Overall, there is still a lot to discover about Mercury. Because the smallest planet in our solar system simply does not reveal all its secrets. “In addition to discovering many grapevines, man has also encountered many similar landforms that we cannot yet locate,” says David Rothery, the project’s lead supervisor and a member of BepiColombo’s scientific team. “This is because the details in the MESSENGER mission images are not completely clear.”

But this mystery may be solved soon. The BepiColombo space probe is currently on its way to the innermost planet in our solar system. The mission should reveal, among other things, how Mercury formed, what geological processes occur on the planet and exactly how the planet is built. “When the European and Japanese BepiColombo space missions take more detailed images of Mercury in early 2026, we will study this potential capture in more detail,” says Rothery. “This will help us better understand how extensive and widespread recent tectonic activity on Mercury has been. It could also help confirm whether the research team is right or not. This is how science works; we use new data and observations to verify or modify existing theories.” .