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The Intense Heat from the Sun Helps Ice Form on Mercury. Wait… What?

While the scorching planet Mercury might not be the first place you’d think to look for ice, the MESSENGER mission confirmed in 2012 that the planet closest to the Sun does indeed hold water ice in the permanently-shadowed craters around the Mercury’s poles.  But now a new study regarding Mercury’s ice provides even more counter-intuitive…

While the scorching planet Mercury might not be the first place you’d think to look for ice, the MESSENGER mission confirmed in 2012 that the planet closest to the Sun does indeed hold water ice in the permanently-shadowed craters around the Mercury’s poles.  But now a new study regarding Mercury’s ice provides even more counter-intuitive details about how this ice is formed. Scientists say heat likely helps create some of the ice.

Brant Jones, a researcher in Georgia Tech’s School of
Chemistry and Biochemistry and the study’s first author, said this isn’t some strange,
crazy idea. While it’s a bit complicated, it’s mostly just basic chemistry. The
planet’s extreme daytime heat combined with the super-cold (minus 200-degree
Celsius) temperatures in the permanently shadowed craters might be acting like
an “ice-making chemistry lab.”

Despite Mercury’s daytime heat, there is permanent ice at the poles, according to data and images from the MESSENGER mission. Credit: NASA / MESSENGER

“There is a surprising amount of ice on Mercury and
significantly more than on the Moon,” Brant told Universe Today.

The process for creating ice on Mercury is similar to what happens on the Moon. Back in 2009, scientists determined electrically charged particles from the Sun’s solar wind was interacting with the oxygen present in some dust grains on the lunar surface to produce hydroxyl. Hydroxyl (OH) is just one atom of hydrogen with an oxygen atom, instead of the two hydrogen atoms normally found in water.

Brant worked with other scientists, including colleague Thomas Orlando, also from Georgia Tech, to refine the understanding of that process, and in 2018, published a paper that showed this process on the Moon does not produce significant amounts of hydroxyl and/or water molecules.

“Though the solar wind was suggested as a potential source
term in the 2009 observations of water on the Moon,” Orlando said via email, “the
mechanisms were never really identified. We modeled this for the Moon but the
importance was not as significant on the Moon due to the overall much lower
temperatures.”   

But they knew this process could also take place on asteroids, Mercury or any other surface that is bombarded by the solar wind.

“In order to create molecular water, you need one more
ingredient, and that is heat,” said Brant. 

Scientists model a feasible chemical reaction, in which the Vulcan heat on Mercury could help it make ice at its poles. Georgia Tech’s Thom Orlando (l.) is the new Mercury study’s principal investigator. Brant Jones (r.) is first author. Credit: Georgia Tech / Rob Felt

Daytime temperatures on Mercury can reach 400 degrees
Celsius, or 750 degrees Fahrenheit.

Minerals in Mercury’s surface soil contain what are called
hydroxyl groups (OH). The extreme heat from the Sun helps to free up these
hydroxyl groups then energizes them to smash into each other to produce water
molecules and hydrogen that lift off from the surface and drift around the
planet.

Some water molecules are broken down by sunlight and dissipate. But other molecules land near Mercury’s poles in deep, dark craters that are shielded from the Sun. The molecules get trapped there and become a part of the growing, permanent glacial ice housed in the shadows.

“It’s a little like the song Hotel California. The water molecules can check in to the shadows but they can never leave,” said Orlando, in a press release.

“The total amount that we postulate that would become
ice is 1013 kilograms (10,000,000,000,000 kg or 11,023,110,000 tons) over a
period of about 3 million years,” Jones said. “The process could
easily account for up to 10 percent of Mercury’s total ice.”

The data used for their study comes from the MESSENGER spacecraft, which orbited Mercury between 2011 and 2015, studying the planet’s chemical composition, geology, and magnetic field. MESSENGER’s findings of polar ice corroborated previous signatures for ice picked up years earlier by Earth-based radar.

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