Cathy Canavan, age 12, of Staten Island, New York, for her question:

Why doesn't the sun melt the Planet Mercury?

If there is any lead on the surface of Mercury, it must be oozing around in molten puddles. The melting point of lead is 327.5 degrees centigrade, and the sunny side of Mercury is estimated to reach 350 degrees. This is hot enough to melt both lead and tin. Naturally, no liquid water could exist in such heat. However, aluminum and iron, silver, gold and most of our everyday substances could remain solid, though goodness knows they would be too hot to touch.

Mercury has no protective atmosphere and it is much too close to the sun for human comfort. Its average distance is more or less 36 million miles, though the actual distance ranges between 28,750,000 and 43,750,000 miles. The variations match its elliptical orbital swing, which equals a period of 88 earth days. Being so close to the sun, one would expect the little planet to frizzle to a cinder. But this is not so and observers report that the surface of Mercury even has permanent markings, presumably solid geographical features.