Dust in the (Cosmic) Wind

The Perseid meteor shower is summer’s closing act, arriving in mid-August like clockwork. For centuries, many Christians associated it with the martyred St. Lawrence, whose feast day falls on Aug. 10, so they called the display “the tears of St. Lawrence.” By the mid-1800s, the Italian astronomer Giovanni Schiaparelli came to understand that meteor showers are really comet dust — the “very minute particles that they have abandoned along their orbit.”

Meteor showers occur when Earth intersects with these so-called debris trains at particular times of the year. In the case of the Perseids, the meteor shower that peaks Wednesday and continues this week, the dust comes from Comet Swift-Tuttle, whose remains appear to shower down from the constellation Perseus as it moves across the northern sky.

Dust may seem less poetic than a saint’s tears, but dust has stories to tell.

The story of the solar system begins with dust: Stars died. They exploded. Their remains gathered from far distances to start again. Gravity took hold, and eventually dust, gas, ice and rocks congealed into planets and other objects like comets, which sometimes sprinkle Earth with their debris.

The dust of the Perseids flares up enough to get our attention each August, because it moves through the atmosphere so quickly. Other cosmic dust takes a more gentle stroll. Because their mass is so little relative to their surface area, the smallest particles can actually find their way down to the ground. As Donald Brownlee, an astronomer at the University of Washington who studies cosmic dust particles, has noted, “If you had lettuce for lunch, you probably ate a few.”

In fact, as much as 40,000 tons of dust from space reaches the ground every year. Some of it contains material from stars as well as organic matter — carbon, amino acids and other building blocks of life.

The Indo-European base for the word “dust” is “dhus-no,” which is related to the base for “fury.” That seems right. After all, it was a dizzying dust storm some five billion years ago that gave rise to the solar system and, ultimately, to us.

Christopher Cokinos, a professor of English at Utah State University and the author, most recently, of The Fallen Sky: An Intimate History of Shooting Stars.