Homogeneity of 67P/Churyumov-Gerasimenko as seen by CONSERT: implication on composition and formation

¹ Univ. Grenoble Alpes, CNRS, CNES, IPAG, 38000 Grenoble, France
e-mail: alain.herique@univ-grenoble-alpes.fr
² Space Research Centre, PAN, Warsaw, Poland
³ Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, Germany
⁴ DLR Institute of Planetary Research, Berlin, Germany
⁵ LATMOS/IPSL, UVSQ, UPMC, CNRS, Guyancourt, France

Received: 14 December 2018
Accepted: 19 April 2019

Abstract

Context. After the landing of Philae, CONSERT probed the nucleus of 67P/Churyumov-Gerasimenko (67P) and observed no heterogeneities at metric scale within the probed part of the small lobe of 67P. Further studies have then quantified the observed homogeneity in terms of maximum permittivity contrast versus the typical size of heterogeneities.

Aims. The aim of this article is to interpret the sensitivity limits of CONSERT measurements in terms of composition, and to provide constraints on the maximum variability in composition, porosity, and local dust-to-ice ratio.

Methods. The sensitivity of CONSERT measurements to local variations in density, dust-to-ice ratio, and composition was analyzed using permittivity modeling of mixtures.

Results. We interpret the maximum detectable heterogeneity size and contrast in terms of composition and porosity of the nucleus. The sensitivity to porosity is ±10 percent points for heterogeneities with a characteristic length scale of a few meters; the sensitivity to local variations in the composition is limited.

Conclusions. In terms of accretion, our results are compatible only with scenarios generating porosity heterogeneities at scales lower than one meter, or with porosity variations smaller than ±10 percent points. This is clearly compatible with an accretion model of a gentle gravitational collapse of a pebble cloud.