WARC DISCOVERIES

Comet dust reveals unexpected mixing of solar system material

A new analysis of dust from the comet Wild 2, collected in 2004 by NASA’s Stardust mission, has revealed an oxygen isotope signature that suggests an unexpected mingling of rocky material between the center and edges of the solar system. WARC researchers Takayushi Ushikubo, Noriko Kita, and John Valley, along with collaborators Tomoki Nakamura and others, analyzed ratios of three oxygen isotopes (¹⁶O, ¹⁷O, and ¹⁸O) in 10-40 micron crystals of olivine and pyroxene from the comet’s halo by ion microprobe at the Wisc-SIMS laboratory. These samples, which reached Earth in early 2006, are the first solid samples returned from space since the Apollo missions. As documented in their paper in Science, researchers were surprised to find oxygen isotope ratios in the comet crystals that are similar to asteroids and even the sun itself. Because these samples more closely resemble meteorites than the primitive, low-temperature materials expected in the outer reaches of the solar system, their analysis suggests that heat-processed particles may have been transported outward in the young solar system over four billion years ago.

Citation:
Nakamura T, Noguchi T, Tsuchiyama A, Ushikubo T, Kita NT, Valley JW, Zolensky ME, Kakazu Y, Sakamoto K, Mashio E, Uesugi K & Nakano T (2008) Chondrule-like objects in short-period comet 81P/Wild 2. Science 321: 1664-1667. A PDF copy of the paper can be found here.

Posted October 21, 2008