THE fastest man-made object ever to plunge through Earth鈥檚 atmosphere landed safely in the Utah desert at 3.10 am on 15 January. Within hours of parachuting down, NASA鈥檚 Stardust capsule was retrieved and flown to a clean room in a nearby hangar. It was a triumphant finale to a seven-year mission to bring back pristine dust from comet Wild 2, with the hope of gaining insights into the origins of our solar system.
But even as it descended, the capsule was already the focus of a diverse array of experiments designed to study something entirely different: meteors. It did not disappoint.
The capsule raced across the skies of northern Nevada in a blazing neon-pink fireball that seemed to match the glow of the casino-dotted wilderness below. 鈥淭his was like a really great meteor,鈥� says Wayne Edwards at the University of Western Ontario in Canada. 鈥淏ut we knew all the properties of the object prior to its actual arrival.鈥�
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Armed with precise knowledge about the capsule, including its mass and velocity, Edwards and a colleague were near Wendover, Nevada, to record Stardust鈥檚 arrival and use it as a baseline for analysing the energetics of natural meteors. This involved burying seismometers nearly half a metre below ground in hopes of detecting a tiny local earth tremor caused by the sonic boom or 鈥渁irwave鈥� of the capsule鈥檚 re-entry. 鈥淭he interaction of how the airwave couples to the ground and produces a surface wave is not well understood,鈥� says Edwards.
Nearby, Doug ReVelle, a researcher from the Los Alamos National Laboratory in New Mexico, recorded the passage of the airwave in infrasound 鈥� the inaudible, low-frequency component of the capsule鈥檚 sonic boom. Infrasound travels much further than audible sound, and data from Stardust鈥檚 airwave will help scientists determine the energy and size of incoming meteors from great distances, even when they are not observed visually.
Several kilometres away, a group from the University of Calgary in Canada led by Alan Hildebrand filmed the fiery capsule as it passed overhead. During their half-minute window of visibility the capsule slowed perceptibly from its initial speed of 12 kilometres per second to 3 kilometres per second, while changing colour from near-white to a deep, rosy red before fading from sight completely.
鈥淚t鈥檚 really gratifying to see that deceleration,鈥� says Hildebrand, who works on recovering fragments from meteors that explode during re-entry. Hildebrand will use his results to see how well the standard methods of determining a meteor鈥檚 trajectory stack up against the known trajectory of the Stardust capsule.
While many teams observed the capsule鈥檚 arrival from the ground, a planeload of NASA scientists from the Ames Research Center (ARC) in Moffett Field, California, made aerial observations from a DC-8. 鈥淲hat I saw was a bright light with a glowing head and persistent trail,鈥� says ARC鈥檚 George Raiche.
During the flight, Raiche manned a spectroscope to break down the light of the incandescent glow that surrounded the capsule into its constituent wavelengths, which will help reveal the profile of temperatures experienced by the capsule鈥檚 resin-impregnated carbon heat shield. This is of particular interest to engineers because Stardust鈥檚 high-velocity re-entry means it endured roughly 10 times the heating rate typically experienced by the space shuttle. The speeds and temperatures are similar to what could one day face capsules bringing astronauts back from NASA鈥檚 proposed missions to the moon. 鈥淚鈥檇 say we had a very good night,鈥� says Raiche, 鈥淚t鈥檚 a great yield of data.鈥�
鈥淪tardust鈥檚 high-velocity re-entry means it endured 10 times the heating rate typically experienced by the space shuttle鈥�
Once the capsule landed, the focus shifted to members of Stardust鈥檚 science team, who were anxious to get their hands on its precious cargo. 鈥淲hat NASA has done is sent a time machine to the beginning of the solar system and brought it back to us,鈥� says John Bradley of the Lawrence Livermore National Laboratory in California. 鈥淵ou can bet some of our most cherished hypotheses are going to go out the window.鈥�
