Analysis of Comet Grain to Date Jupiter’s Formation

Analysis of Particles from comet grains brought to Earth by the NASA’s Stardust spacecraft. Isotopes contained in the comet Wild 2 revealied that Jupiter could not be formed within 3 million years after the formation of the first solids in our Solar System.

University of Hawaii scientists analyze a tiny comet grain to date Jupiter

We know that our solar system was formed following a Little Bang, that is to say the explosion of a supernova that led to the collapse of the nebula, a molecular cloud, dust, cold and dense. This explosion was accompanied by the nucleosynthesis of an unstable isotope of aluminum, 26Al, with half-life of 730,000 years. The team also measured magnesium isotopes (26Mg is the decay product of the short-lived radioactive isotope 26Al) . The last date obtained using isotope content at renowned -rich inclusions of aluminum and calcium (called CAI Calcium Aluminum-rich Inclusions) in meteorites indicates that the event occurred there 4.568 million of years or so.

Meteorites are not the only memories of the early history of the solar system. Comets are too, so the Stardust spacecraft was part of the grains harvest of Wild 2 that it has returned to Earth in 2006. One of these grains, named Iris, has been studied carefully. In particular, some of the isotopic abundances of oxygen and magnesium were measured by mass spectrometry to secondary ionization.

The analysis results of Iris were published in the February 1, 2012 issue of the Astrophysical Journal Letters are new results from laboratory analyses on a tiny fragment in one of the comet Wild 2 particles. Dr. Ryan Ogliore, a postdoctoral researcher at the Hawaii Institute of Geophysics and Planetology (HIGP, University of Hawaii) conducted the research with Drs. Gary Huss and Kazuhide Nagashima, also from HIGP, and colleagues from the University of California at Berkeley, University of Washington, and the Lawrence Berkeley National Laboratory. It appeared that grain from Stardust was similar to chondrules found in meteorites such as Allende. It was formed by condensation from a material increase to over 1100 ° C and which has probably cooled in a few hours.

All indications are that it comes from a region of the protoplanetary disc near the Sun, where there are rocky planets formed. Its presence in a comet is formed at a great distance from the Sun, near the current Kuiper belt (35-50 AU from the Sun) indicates that Iris is made of materials that have migrated from areas internal to external areas of protoplanetary disk.

Wild 2, aluminum 26 and the formation of Jupiter

These migration processes are not new but the consequences can be derived of the abundances of magnesium isotopes are measured in Iris, is new. Indeed, initially, the protoplanetary disc must have a homogeneous content in 26Al.

But Iris shows no isotopic anomaly would have resulted from the decay of aluminum 26 incorporated into the grain during its formation. We must therefore conclude that it has formed for at least 3 million years after the first condensation of solid material in the inner part of the protoplanetary disc, that is to say, when the nuclei 26Al had completely disappeared or almost.

According to researchers, the main information one can deduce from this lack of 26Al is at least 3 million years after these early condensations, by Jupiter existed yet. His presence would have meant so much to accrete material from a protoplanetary disc would have formed blank area, bisecting the disc. The process of mass transfer zones internal to external areas have been stopped. Iris shows that this was apparently not the case, informing us at the same time on the chronology of the formation of Jupiter.

Comet Wild 2 during its flyby by the Stardust spacecraft. © NASA / JPL-Caltech

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Tagged Comet Grain, Jupiter, Jupiter's Formation, Space, Stardust, Wild2