Researchers have uncovered three new large deposits of ice on Mercury. The team believes that there could be a lot more frozen water than previously thought hidden in smaller deposits around the planet’s poles.
Mercury is the closest planet to the Sun, and during the day it has a surface temperature of 427ºC (801°F). But water can always find its way around things and ice has been discovered in craters in darkness on the planet's surface.
Now three more craters have been spotted with ice inside them by researchers at Brown University. The findings are reported in Geophysical Research Letters. There are small areas inside and between the craters, where sunlight doesn’t reach, that appear to be rich in ice. The small deposits might not seem like much individually but together they add up.
“The assumption has been that surface ice on Mercury exists predominantly in large craters, but we show evidence for these smaller-scale deposits as well,” Ariel Deutsch, the study’s lead author, said in a statement. “Adding these small-scale deposits to the large deposits within craters adds significantly to the surface ice inventory on Mercury.”
The first evidence of water ice on Mercury came from Earth-based radar telescopes when they detected highly reflective regions. Confirmation came in 2011 when NASA’s MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) probe discovered signals from Mercury's north pole consistent with water ice.
Deutsch and her two colleagues – James Head from Brown and Gregory Neumann from NASA’s Goddard Space Flight Center – looked through the MESSENGER data and used the spacecraft's altimeter data to track how reflective the surface of Mercury was. This allowed them to discover the three large deposits that have a combined area of about 3,400 square kilometers (1,310 square miles).
But the data showed something else. There were small regions more reflective than the average surface of Mercury and less bright than the large ice deposits. Four such regions have been detected, each less than 5 kilometers (3 miles) across.
“We suggest that this enhanced reflectance signature is driven by small-scale patches of ice that are spread throughout this terrain,” Deutsch said. “Most of these patches are too small to resolve individually with the altimeter instrument, but collectively they contribute to the overall enhanced reflectance. These four were just the ones we could resolve with the MESSENGER instruments.”
“We think there are probably many, many more of these, ranging in sizes from a kilometer down to a few centimeters,” she added.
The joint European-Japanese mission BepiColombo will get to Mercury in the next decade and might be able to provide us with more data.