Comets

The year’s first meteor shower should be at its best in the hours before dawn tomorrow. The Quadrantids “rain” into the atmosphere from the extinct constellation Quadrans Muralis, which is fairly close to the handle of the Big Dipper.

The Quadrantids may be the spawn of an asteroid, which in turn could be the dead remnant of a comet.

Comets are balls of frozen water and gases mixed with rock. They’re left over from the birth of the planets. In fact, the planets probably formed as many of these iceballs stuck together to form larger and larger bodies.

But hundreds of billions of iceballs remained. Many were hurled into interstellar space by the gravity of the giant planets. Others were thrown into distant orbits around the Sun. Occasionally, one of these gets a gravitational nudge — or a bump from one of its kin — and heads toward the Sun.

As it nears the Sun, some of its outer layers of ice vaporize. That releases water vapor and other gases into space, along with small grains of r