¹B. C. Kaiser,¹J. C. Clemens,²S. Blouin,^3,4P. Dufour,¹R. J. Hegedus,¹J. S. Reding,³A. Bédard
Science 371, 168-172 Link to Article [DOI: 10.1126/science.abd1714]
¹Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC, USA.
²Los Alamos National Laboratory, Los Alamos, NM, USA.
³Département de Physique, Université de Montréal, Montreal, QC, Canada.
⁴Institut de Recherche sur les Exoplanètes, Université de Montréal, Montreal, QC, Canada.
Reprinted with Permission from AAAS

Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

¹Lucy McGee,^2,3Munir Humayun,¹John Creech,^4,5Brigitte Zanda
Science 371, 164-167 Link to Article [DOI: 10.1126/science.abc8116]
¹Department of Earth and Environmental Sciences, Macquarie University, Sydney, NSW 2109, Australia.
²Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL 32310, USA.
³National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
⁴Institute de minéralogie, de physique des matériaux et de cosmochemie, Muséum National d’Histoire Naturelle, 75005 Paris, France.
⁵Institute of celestial mechanics and ephemeris calculations, Observatoire de Paris, 75014 Paris, France.
Reprinted with Permission from AAAS

Carbonaceous chondritic meteorites are primordial Solar System materials and a source of water delivery to Earth. Fluid flow on the parent bodies of these meteorites is known to have occurred very early in Solar System history (first <4 million years). We analyze short-lived uranium isotopes in carbonaceous chondrites, finding excesses of 234-uranium over 238-uranium and 238-uranium over 230-thorium. These indicate that the fluid-mobile uranium ion U6+ moved within the past few 100,000 years. In some meteorites, this time scale is less than the cosmic-ray exposure age, which measures when they were ejected from their parent body into space. Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation. We favor the impact heating hypothesis, which implies that the parent bodies still contain ice.