The paper published in 2008 and entitled " 26Al-26Mg and 207Pb-206Pb Systematics of Allende CAIs: Canonical Solar Initial 26Al/27Al Ratio Reinstated ," was written while Jacobsen was a graduate student at UC Davis and working in collaboration with Hutcheon.
The work established a precise value for the initial 26Al/27Al ratio of the early solar system. 26Al is a short-lived (half-life = 730,000 years), now-"extinct" isotope that was present when the solar system initially formed. Its abundance in the early solar system can be inferred from measurements of its stable daughter product, 26Mg, in early-condensed solar system solids (calcium-aluminum-rich inclusions, or CAIs) that are preserved in primitive meteorites. Precise knowledge of the initial 26Al/27Al ratio is important because the 26Al (26Mg)-27Al systematics of meteorites can then be used to time events in the very early solar system and constrain the location and history of condensation in the early solar system.
The initial 26Al/27Al ratio also has implications for the inventory of radioactive heat sources responsible for melting and chemical differentiation of the solar system's earliest proto-planets and planetesimals (solid objects thought to exist in protoplanetary disks and in debris disks). Other authors include researchers from the Geological Survey of Canada, the University of Hawaii and the Institut fur Geologie und Mineralogie at the Universitat zu Koln in Germany.