^1,2,3Marc Neveu,⁴Christopher H.House,^2,3,5Scott T.Wieman
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113714]
¹Department of Astronomy, University of Maryland, 4296 Stadium Dr., College Park, MD 20742, USA
²Planetary Environments Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20770, USA
³Center for Research in Space Science and Technology, NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20770, USA
⁴Department of Geosciences, Pennsylvania State University, 503 Deike Building, University Park, PA 16802, USA
⁵Center for Space Sciences and Technology, University of Maryland, Baltimore County, 1000 Hilltop Cir., Baltimore, MD 21250, USA
Copyright Elsevier

Clark et al. [Clark, R.N., Brown, R.H., Cruikshank, D.P., Swayze, G.A., 2019. Icarus, 321, 791–802] reported an extremely low value of the ¹²C/¹³C ratio in CO₂ ice on Phoebe, a likely captured moon of Saturn. Unless Phoebe did not form in the solar system, we interpret this value as indication that Phoebe accreted surface carbon from a region of the protosolar nebula where ¹³C was enriched due to self-shielding of ¹²CO from photodissociation. This could imply that Phoebe is also enriched in ^17,18O relative to most solar system objects sampled to date. Phoebe and other objects that may have sampled these ¹³C-rich regions, such as Pallas or Triton, may provide the opportunity to directly measure isotopic fractionations in endmembers of the self-shielded solar nebula.