Nebular dead zone effects on the D/H ratio in chondrites and comets

¹ Institut UTINAM, CNRS-UMR 6213, Observatoire de Besançon, Université de Franche-Comté, BP 1615, 25010 Besançon Cedex, France
e-mail: mdib@obs-besancon.fr
² Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA
³ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁴ Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853, USA

Received: 2 May 2015
Accepted: 30 July 2015

Abstract

Context. Comets and chondrites show non-monotonic behavior of their deuterium-to-hydrogen (D/H) ratio as a function of their formation location from the Sun. This is difficult to explain with a classical protoplanetary disk model that has a decreasing temperature structure with radius from the Sun.

Aims. We want to understand if a protoplanetary disc with a dead zone, i.e., a region of zero or low turbulence, can explain the measured D/H values in comets and chondrites.

Methods. We use time snapshots of a vertically layered disk model with turbulent surface layers and a dead zone at the midplane. The disc has a non-monotonic temperature structure due to increased heating from self-gravity in the outer parts of the dead zone. We couple this to a D/H ratio evolution model in order to quantify the effect of such thermal profiles on D/H enrichment in the nebula.

Results. We find that the local temperature peak in the disk can explain the diversity in the D/H ratios of different chondritic families. This disk temperature profile leads to a non-monotonic D/H enrichment evolution, allowing these families to acquire their different D/H values while forming in close proximity. The formation order we infer for these families is compatible with that inferred from their water abundances. However, we find that even for very young disks, the thermal profile reversal is too close to the Sun to be relevant for comets.