Which unexpected chemical compound has recently been discovered on Mercury?

Question

Quizplus · Accepted Answer

Water ice has been discovered at Mercury's north and south poles, which is unexpected due to the planet's proximity to the Sun and its extremely high surface temperatures. This discovery was made possible through radar observations from Earth and spacecraft missions to Mercury, revealing that permanently shadowed craters at the poles are cold enough to sustain water ice.

Which Unexpected Chemical Compound Has Recently Been Discovered on Mercury