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Figure: Mercury ice caps? Radar pulses reflected from the polar regions of Mercury, and detected by the Arecibo Telescope reveal bright regions in craters that may be surface or sub-surfaces races of water ice bound up in the soil. Located in the perpetually shadowed regions of these craters, comet ice may have accumulated there for billions of years. (Credit: John Harmon - Arecibo Observatory)
Although the equatorial temperatures are near 800 F, because the rotation axis of Mercury is nearly perpendicular to its orbit around the Sun, there are certain craters near Mercury's North Pole where the Sun never shines, and where temperatures as low as -235 F can occur. In 1992 astronomers Martin Slade, Bryan Butler and Duane Muhlman at the Jet Propulsion Laboratory and Caltech reported the first full-disk radio image of Mercury using the Goldstone 70-meter radio telescope.
They found that some of the craters had radar reflections as bright as those seen on Mars, and similar to the ices on the satellites of the outer planets. The ice must be mixed with the 'topsoil' like permafrost. The best explanation for their existence involves water-rich comets that crash into Mercury. Some of the water molecules eventually find there way to the cold traps in the shadowed craters. Why is this important? Because it tells us that one of the most important ingredients for life is very hardy. Also, if for some unimaginable reason you would want to land humans on Mercury, this is the best possible place to put them to save on bringing water with you. In the future we will do more surveys of this potential water deposit, and perhaps have a robot lander visit this area and do some digging!
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This answer was updated in 2011.
See my books:
The Astronomy Cafe (1998) and
Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011
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