The Moon anchors a beautiful lineup late tonight. It includes Mars and the two brightest stars of Taurus. The lineup climbs into view by around midnight, and is high in the sky at first light. Mars glows bright orange — the result of iron-rich dust that coats most of the planet. The major exceptions are the polar ice caps, which are almost pure white. There’s a lively debate about what’s at the bottom of the cap at the south pole. Some researchers say there could be liquid water mixed with the dirt. Others say that water wouldn’t work — it’s more likely to be clay, salty minerals, or even volcanic rock. The debate is based on observations made by Mars Express. It used radar to peek below the ice cap, which is made of layers of frozen water and carbon dioxide. The radar showed bright reflections below the ice cap. The original study team interpreted the reflection as liquid water mixed with high levels of salts. A comparison to radar readings of a lake below the ice in Antarctica reache
