Detection of volatiles undergoing sublimation from 67P/Churyumov-Gerasimenko coma particles using ROSINA/COPS. I. The ram gauge

TL;DR

This study analyzes in-situ measurements from the Rosetta mission to detect and classify volatile sublimation in comet 67P/Churyumov-Gerasimenko particles, revealing diverse compositions and estimating volatile volumes.

Contribution

It introduces a method to identify and categorize sublimating icy particles using ram gauge data, providing new insights into cometary volatile content.

Findings

Detected 73 icy particles with volatiles impacting the instrument.

Classified 25 particles into three types based on sublimation characteristics.

Estimated volatile volumes to be on the order of hundreds of nanometres.

Abstract

The ESA Rosetta mission has allowed an extensive in-situ study of comet 67P/Churyumov-Gerasimenko. In measurements performed by the ram gauge of the on-board COmet Pressure Sensor (COPS), features have been observed that deviate from the nominal ram gauge signal. These are attributable to the sublimation of the volatile fraction of cometary icy particles containing volatiles and refractories. The objective of this work is the investigation of the volatile content of icy particles that entered the COPS ram gauge. The ram gauge measurements are inspected for features that we associate to the sublimation of the volatile component of cometary particles impacting the instrument. All sublimation features with high enough signal to noise ratio are modelled by fitting one or more exponential decay functions. The parameters of these fits are used to categorise different compositions of the sublimating component. From features attributable to ice sublimation, we infer the detection of 73 icy particles containing volatiles. 25 detections have enough volatile content for an in-depth study. From the values of the exponential decay constants, we classified the 25 inferred icy particles into three types, interpreted as different volatile compositions, possibly further complicated by different morphologies. Available data do not give indication as to which molecules compose the different types. Nevertheless, we can estimate the total volume of volatiles, expressed as the diameter of an equivalent sphere of water (density of 1 g cm$^{-3}$). This was found to be on the order of hundreds of nanometres.