Collected comet dust surprises solar system researchers
First studies of the comet dust transported to Earth by NASA's Stardust probe have shaken ideas that researchers had previously had about the formation of comets. The samples also contain rock material that only forms at very high temperatures. Until now, however, it had been assumed that comets emerged exclusively from cold matter far from the center on the fringes of the primordial solar nebula.
In the dust particles of the sampled comet Wild 2, the scientists found, among other things, olivines that are enriched with iron and magnesium. Such compounds probably formed inside the cloud of matter from which the solar system formed, at temperatures of more than 1000 degrees Celsius. They must then have reached the cold outer regions via a mechanism that is still not understood, where they met up with connections that had arisen in the cold to the comets that are still present in the solar system today.
The olivine mixed crystal forsterite, which has a melting point of 2000 degrees Celsius, was discovered in the Stardust samples, as was previously the case in comet particles found on Earth. The researchers also found calcium-aluminum inclusions (CAI) formed at even higher temperatures. The finds raise a number of questions that cannot be answered at this time, according to Mike Zolensky of the research team.
Possibly the observations support the so-called "X-wind" hypothesis, solar system researchers speculate. The hypothetical X-wind, a powerful flow of gas, could blow away molten material from the core of protostellar clouds as planetary systems form. However, it had not previously been assumed that X-winds transport matter to the cold fringes of an emerging system. Alternatively, Wild 2's once-hot material could originally have come from other stars. Still outstanding isotope investigations should now help to answer some new questions.