Science / Medicine : Mercury May Have Polar Ice Cap

New evidence suggests Mercury has a north pole ice cap formed by “snow” on the planet closest to the sun, according to findings presented last week by scientists surprised by their own discovery. “The general reaction . . . was ‘Oh, my God, that can’t be ice, can it?’ ” said Caltech planetary scientist Duane Muhleman at a meeting of the American Astronomical Society in San Francisco. “But once you think about it and do the analysis it makes perfect sense.”

According to Caltech’s evidence from August experiments using ground-based radar, the first-ever radar photographs of an entire hemisphere of Mercury indicate a highly reflective substance such as ice is present over an estimated 150-square-mile area.

Computer modeling by UCLA researchers David Paige and Stephen Wood found that Mercury’s polar regions may be as cold as minus 235 degrees Fahrenheit, compared to temperatures of up to 800 degrees at the planet’s equator. Because Mercury’s equator always faces the sun during orbit, the heavily cratered north pole is protected from the heat that could melt hidden ice formations, the scientists said.