The first thought to cross one’s mind on a mention of planet Mercury is its blistering daytime temperature of up to 800 degree F (427 degree Celsius) because of its proximity to the Sun. However, new research has indicated that there may be more ice on Mercury’s scorching surface than thought.

Scientists in their study, published in the journal Geophysical Research Letters, claim to have found evidence of frozen water hidden away on crater floors that are permanently shadowed from the Sun’s blistering rays.

The slow spin, thin atmosphere and perpetually dark poles mean that on the night side, Mercury’s temperature can drop to -290 degree F (-180 degree Celsius), creating the perfect conditions for icy deposits. The research also indicates that smaller-scale icy deposits are scattered around Mercury’s north pole, both inside craters and in shadowed terrain between craters.

Those deposits may be small, but they could add up to a lot more previously unaccounted – for ice, researchers said.

The theory of ice on Mercury first came up in the 90’s, as an explanation for extremely reflective regions picked up by radar telescopes. These shiny spots were spotted at the floors of several craters near the planet’s poles, where no direct sunlight ever fell, and the freezing temperatures in those dark patches was plenty cold enough for ice to form.

The planet’s axis does not have much tilt, so its poles get little direct sunlight, and the floors of some craters get no direct sunlight at all. Temperatures in those eternal shadows have been calculated to be low enough for water ice to be stable.

NASA’s MESSENGER probe, which entered Mercury’s orbit in 2011, detected neutron signals from the planet’s north pole that were consistent with water ice.

For the new study, researchers looked specifically at readings from the spacecraft’s laser altimeter. The device is mostly used to map elevation, but it can also be used to track surface reflectance. The addition of those craters to Mercury’s ice inventory is significant. Deutsch estimates the total area of the three sheets to be about 3,400 square kilometers.

Researchers also looked for patches that were smaller than the big crater-based deposits, but still large enough to resolve with the altimeter. They found four, each with diameters of less than about five kilometers.

“These four were just the ones we could resolve with the MESSENGER instruments,” Deutsch said.
“We think there are probably many, many more of these, ranging in sizes from a kilometer down to a few centimeters,” he said.

Knowing that these small-scale deposits exist, and that they are likely the source of the slightly brighter surface outside craters, could dramatically increase the ice inventory on Mercury.

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