Judy Russell, age 11, of Tokyo. Japan, for her question:
What causes the craters on the moon?
The New World was just a few thousand miles away, but Columbus had no idea what he would find there. The astronauts who will cross some 235,000 miles to land on the moon have a good idea of what they will find, For man has been gazing at the moon for countless ages, As telescopes got better and better, revealing more and more details of the lunar landscape, scientists have been able to use what they know to speculate about the features of the moon and how they were caused.
The mountains and the flat plains on the moon do not surprise us, for the earth has many such features. The lunar craters, however, tease and puzzle us. Most of them are round pits ringed with steep walls, somewhat like Meteor Crater in Arizona. For a long time many experts thought that the lunar craters also were caused by falling meteors. Up‑to‑date theories disagree, They also disagree with the older theory that the craters were caused by lunar voloanoes.
Meteor craters on earth are very rare. The face of the moon is pitted with some 300,000 craters more than a mile wide, plus countless smaller ones. Surely so many meteors could not hit the moon and miss the earth, On earth, most volcanic craters are on the tops of mountains, The moon has a few such craters, but most of them are pits below the level of the surrounding landscape,
The latest theories suggest that the lunar features were caused by forces at work inside the moon, The inside may have stayed hot after the surface formed a cool, solid crust, Buried pools of magma made from molten rock and seething gases would tend to push up cracks in the crust and pour forth in ridges of lava. The mountains could have been formed as this hot lava cooled into solid rock.
The craters, too, may have been formed by pockets of buried lava.
A seething pocket of magma might bubble up to form a dome on the surface. Under the chilly lunar night the dome would collapse, leaving a flat floor surrounded by a steep ring of cooling lava. Later, a smaller outburst might bubble up through the weak floor of the pit,
Laboratory experiments show that molten material under a solid surface will behave in just the same way. If this theory is corrento the craters were caused by seething lava which bubbled up into domes and then collapsed. The floors of many craters are pierced by steep spires. These could have come from a second or third outburst. All this activity must have happened in the remote past. The moon then settled down to be almost; though not quite, at rest.
Some of the lunar craters are more than 100 miles wide and countless others are just a few hundred yards wide, Their ramparts range from one to six miles high. Some stand alone. Others overlap, with a mix‑up of walls and floors, The astronauts will find the lunar craters very fascinating, indeed, and perhaps they will discover whether this latest theory about their formation is correct,