NASA's Stardust Mission Safely Home

In January 2004, NASA's Stardust spacecraft (Fig. 1) flew into the cloud of dust and gases jetted from the surface of Comet Wild 2. Nine days before its closest approach to the comet, the spacecraft deployed an array of silica aerogel targets (Fig. 2) that collected many thousands of tiny particles ejected from the comet. The particles struck the aerogel array at speeds up to six times faster than a high-powered rifle bullet. The Stardust spacecraft then retracted the collection array and began its long journey home.

As the spacecraft approached Earth, it ejected a spinning recovery capsule containing the aerogel array. The capsule and its valuable cargo entered Earth's atmosphere at a velocity of 46,440 km per hour (28,860 mph), the fastest known spacecraft reentry in history.

Early in the morning of 15 January 2006, the Stardust probe parachuted safely to a Utah desert, where a NASA recovery crew was waiting to retrieve it after its 4.63 billion kilometers (2.88 billion miles) voyage through space.

The Stardust capsule was then flown to the Stardust Laboratory at NASA's Johnson Space Center in Houston, where the aerogel collection panel was opened and inspected in the Stardust Lab's class 100 clean room.

The scientists who first saw the surface of the aerogel array were delighted to see obvious impacts of comet dust, one of which was large enough to be seen across the room (Fig. 3). According to a NASA media release, "The collection of comet particles has exceeded our expectations," said Dr. Donald Brownlee, Stardust principal investigator from the University of Washington, Seattle. "We were absolutely thrilled to see thousands of impacts on the aerogel."

Preliminary indications are that the Stardust mission captured around 1 milligram of material. The largest particle reported by the Stardust team is about 1 mm across. Some particles are about the width of a human hair, and most are much smaller.

Stardust's comet mission is only half the story, for the back side of the aerogel collection panel also collected interstellar particles during 195 days of its long mission. While many thousands of comet particles were captured, NASA estimates that only 45 or so interstellar particles were collected. Finding only 45 microscopic particles in a collector panel having an area of 1,000 square centimeters (160 square inches) presents a major challenge, which is why NASA and the University of California, Berkeley, need your help. For details, see the accompanying news story in this issue of The Citizen Scientist.

Forrest M. Mims III