Key 'Stardust' Spacecraft Discovery May Have Resulted From Contamination

Stardust was the first U.S. mission to capture samples of a comet (Comet Wild 2) and return that material, believed to hold clues to the origin of the solar system, to Earth for scientific analysis. In the report, Jesus Martinez-Frias and colleagues point out that scientists were surprised to find that Stardust had collected tiny grains of the mineral osbornite, which chemically is titanium nitride. Osbornite forms only at ultra-hot temperatures of about 3,140 Fahrenheit.

Scientists thus concluded that the osbornite could have formed near the sun, and ejected to the outer reaches of the solar system — an indication that the infant solar system was a much more violent and tumultuous place then previous believed.

Martinez-Frias and colleagues stress the plausibility and significance of such hypothesis, but suggest another possible explanation for osbornite presence, which they say has not yet been considered. They point out that Stardust’s rocket thrusters used a propellant of ultra-pure hydrazine, which chemists long have used for the so-called nitration reactions used to make titanium nitride on Earth. The propellant likewise could have reacted in space with titanium from the comet or spacecraft to form titanium nitride, the researchers state. They recommend that laboratory simulation analyses and further studies are needed before reaching a final conclusion on osbornite origin.