Upcoming Small Orbs: No more may be needed to explain the presence of water ice on Mercury.
Within our solar system we find the planet Mercury. You might not expect ice cream there; After all, the planet is three times closer to the sun than the Earth, and therefore it has to withstand more radiation and heat. However, there is ice on Mercury. In deep craters near the poles, the bottoms of which never see sunlight. There, in those craters, ice several meters thick.
But where does this ice actually come from? Researchers at the Netherlands Institute for Space Research (SRON) have now studied this question. Their results can be read in the journal Icarus†
When it comes to ice on Mercury, there are roughly two possibilities. Either the water molecules originated from space and were deposited on Mercury by impacted asteroids and comets, or orbited space dust. Or that the water molecules are “internal”, that is, they arise from within Mercury or originate from Mercury itself. “Internal sources are volcanic activity or the release of gases from the crust and mantle,” said researcher Katerina Frantseva. Scientias† That such events could bring water to the surface is due to the fact that some of the materials from which Mercury was formed harbored water. Later, for example, some of this material may have surfaced through volcanic eruptions. “In addition, the interaction between the planet’s surface and the solar wind can also generate water.”
However, in their study, Frantseva and colleagues focus not on these inland water sources, but instead on the possibility that asteroids, comets, and space dust may have brought the water to Mercury. They discovered this option using simulation. Using special software, they imitated the solar system – which contains the sun, eight planets and hundreds of thousands of asteroids, comets and dust particles. “In our simulations, we tried to simulate the dynamics in the solar system, i.e. how planets and small celestial bodies move around the sun. And every time there was a collision between a small celestial body and a planet or the sun, we observed it. The simulation is statistically representative of reality: the number of small celestial bodies that collides with planets corresponds to what we see in reality, but we can’t use simulations to predict which specific celestial body will collide with a planet at any given moment. In fact, the program allows us to simulate how many small celestial bodies, on average, collide with a particular planet during a certain time frame.”
Simulations show that Mercury will have to take some time. In fact, over the course of a billion years, tiny water-bearing celestial bodies have struck the planet to explain the amount of ice we now find on the planet. “We can’t rule out inland water sources, such as volcanic activity and gases escaping from the crust and mantle, but this finding shows that we don’t need them,” said Frantseva. “We can suffice with influences from small celestial bodies to explain the water we see on Mercury.”
Ten thousand kilograms of water
Space dust plays a particularly important role in this; Simulations indicate that interplanetary dust particles deposit more than ten thousand kilograms of water on Mercury annually. Asteroids and comets together transport about 1,000 kilograms of water to the planet each year. “The water deposited by small celestial bodies on Mercury will remain only partially on the surface,” said Fantseva. “Some of the water is lost during the impact, some is lost through interaction with ultraviolet rays from the sun and the rest reaches the permanently shaded crater near the poles.”
As mentioned, it’s not entirely certain whether small, falling orbs when it comes to the thick ice sheet in Mercury’s polar craters really deserves all the credit. “Simulation is not the same as observation,” Fantseva asserts. “But we know for sure that small orbs collide with planets.” And with that, it seems very plausible that those comets, asteroids, and space dust deserve at least some recognition. The exact size of their role should become clear in the near future. “To validate our model, we need to compare the water in the polar craters with the water we see on small orbs,” says Fantseva. BepiColombo, a probe currently en route to Mercury and due to arrive there in 2025, may have a role in this.
There is no doubt to Frantseva that the questions about the origin of Mercury’s ice are worth the researchers’ time and effort. “It is important to understand how water – a key component of life as we know it – is distributed throughout our solar system.” What makes Mercury an interesting research object is that ideas about transporting water on or to this planet can be tested during future missions to the planet. “In addition, Mercury is also a great example of a planet where water can live, despite its small distance from the parent star.” The results of current and future research on Mercury’s ice are of course not only important to our understanding of our solar system; It could also have implications for planets orbiting other stars and their potential for habitation.
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