Mercury's extreme climate turns its poles into an "ice making chemistry lab," scientists say

The extreme heat on the planet Mercury likely helps make ice on its polar regions, according to a study which suggests how water could arise, and collect as ice on planets rife with all the necessary components. The researchers from the Georgia Institute of Technology in the US, said while asteroids may have delivered most of Mercury's water, the planet's extreme daytime heat, combining with its ultracold polar craters -- that never see the sunlight -- could also be acting as an "ice-making chemistry lab". In their new study, to be published in the journal Astrophysical Journal Letters on Monday, they modelled the complex conditions on Mercury, including solar winds that pelt the planet with charged particles, many of which are key to the ice making chemical process.

"This is not some strange, out of left field idea. The basic chemical mechanism has been observed dozens of times in studies since the late 1960s," said Brant Jones, study co-author from the Georgia Institute of Technology. "But that was on well-defined surfaces. Applying that chemistry to complicated surfaces like those on a planet is groundbreaking research," Jones said. According to the scientists, minerals in Mercury's surface soil contain what are called hydroxyl groups (OH), which are generated mainly by the subatomic particles protons. Based on their study, they said extreme heat helps to free up these hydroxyl groups, energise them to smash into each other, and produce water molecules and hydrogen. The water and hydrogen then lift off from the surface and drift around the planet, the researchers said.

While some of these water molecules are broken down by sunlight or rise far above the planet's surface, others land near Mercury's poles in permanent shadows of craters that shield the ice from the sun, they explained. Since the Solar System's first planet does not have an atmosphere, and thus no air that would conduct heat, the molecules become a part of the permanent glacial ice housed in the shadows, according to the scientists. "It's a little like the song Hotel California. The water molecules can check in to the shadows but they can never leave," said Thomas Orlando, another co-author of the study.

"The total amount that we postulate that would become ice is 1013 kilograms over a period of about 3 million years. The process could easily account for up to 10 percent of Mercury's total ice," Jones said. The study is based on data from the MESSENGER spacecraft which sent back images and data from Mercury, corroborating previous signatures for ice picked up years earlier by Earth-based radar. According to the researchers, the ice found from the spacecraft's data was dingy and lurked in permanent shadows in polar craters on Mercury, which is pocked by meteorite and asteroid scars, much like Earth's moon. "The process in our model would not be anywhere near as productive on the moon. For one, there's not enough heat to significantly activate the chemistry," Jones said.

The scientists said the subatomic particles protons from solar winds are more plentiful on Mercury than on Earth, where a mighty magnetic field whips solar wind particles, including protons, back out into space. They said Mercury's field is only about 1 percent as strong, and it swirls protons down onto the surface. "These are like big magnetic tornados, and they cause huge proton migrations across most of the surface of Mercury over time," Orlando said.

These protons, according to the researchers, implant themselves into the soil all over the planet, forming as the hydroxyl groups (OH), which then diffuse to the surface, where the heat does the rest. "I would concede that plenty of the water on Mercury was delivered by impacting asteroids," Jones said. "But there's also the question of where asteroids laden with water got that water. Processes like these could have helped make it," he added..

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