Mercury is the planet closest to the Sun yet there's ice on it. How is that possible? It's hard to believe that on a planet where daytime temperatures reach 400°C there is ice. Now, a team of scientists at the Georgia Institute of Technology says that it is probably the heat from the Sun that helps produce that ice.
How does ice form with the help of the sun?
While it is believed that approximately 90% of the planet's ice comes from asteroids, 10% was formed through natural processes on the planet and the researchers presented a new explanation for this process. According to the theory, chemicals on the planet's surface are heated by intense solar radiation, releasing water and hydrogen that can then settle into deep craters protected from the sun's scorching temperatures, where the water is transformed into ice.
The frozen substance was originally discovered in 2011 by NASA's Messenger probe, which was the first spacecraft to orbit the planet. The space probe's radar images showed large ice pockets embedded in craters at both poles of Mercury.
Brant Jones, a researcher at Georgia Tech's School of Chemistry and Biochemistry and first author of the study, said the idea is not as strange or as crazy as we might think. While it's a bit complicated, it's basic chemistry. The model presents a workable way for water to rise and accumulate like ice on a planet filled with all the necessary components.
Did you know that there's more ice on Mercury than on the Moon?
The planet's extreme daytime heat combined with super-cold temperatures (-200°C) in the permanently shaded craters could be acting as a "chemistry lab for making ice".
"The basic chemical mechanism has been observed dozens of times in studies since the late 1960s," Jones said. "But that was on well-defined surfaces. Applying that chemistry to complicated surfaces like those of a planet is groundbreaking research.
The minerals present on Mercury's surface soil contain what are called hydroxyl groups. Extreme heat from the Sun helps to release these hydroxyl groups and then energizes them to collide with each other to produce water and hydrogen molecules that break away from the surface and move around the planet. Some water molecules are broken down by sunlight and dissipate, but others land near the poles of Mercury in deep craters that are protected from the Sun. The molecules are trapped in this dark corner and become part of the growing permanent glacial ice housed in the shadows.
The team estimates that through the process of hydroxyl transformation, more than 11 billion tonnes of ice could have formed on the planet over 3 million years. "The process could easily account for up to 10 per cent of total Mercury ice. Scientists believe this process could also help explain how ice could form on an asteroid. "Processes like these could have helped achieve this," Jones concludes.
Reference: B. M. Jones, M. Sarantos, T. M. Orlando. A New In Situ Quasi-continuous Solar-wind Source of Molecular Water on Mercury. The Astrophysical Journal, 2020; 891 (2): L43 DOI: 10.3847/2041-8213/ab6bda