Subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko

Abstract

Heat transport and ice sublimation in comets are interrelated processes reflecting properties acquired at the time of formation and during subsequent evolution. The Microwave Instrument on the Rosetta Orbiter (MIRO) acquired maps of the subsurface temperature of comet 67P/Churyumov-Gerasimenko, at 1.6 mm and 0.5 mm wavelengths, and spectra of water vapor. The total H2O production rate varied from 0.3 kg s(-1) in early June 2014 to 1.2 kg s(-1) in late August and showed periodic variations related to nucleus rotation and shape. Water outgassing was localized to the "neck" region of the comet. Subsurface temperatures showed seasonal and diurnal variations, which indicated that the submillimeter radiation originated at depths comparable to the diurnal thermal skin depth. A low thermal inertia (~10 to 50 J K(-1) m(-2) s(-0.5)), consistent with a thermally insulating powdered surface, is inferred.

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

“…Temperatures used in this study are lower than the surface temperatures reported by Capaccioni et al (2015) for measurements with the Rosetta-VIRTIS instrument. We assume the sublimation layer to be colder than the VIRTIS temperatures, which is consistent with their findings that the surface of 67P is almost free of ice and the significantly lower temperatures found by Gulkis et al (2015) below the surface. We further assume that the sublimating gas does not thermally accommodate to the top surface temperature while diffusing outward.…”

“…This leads to total production rates of Q total = 8.7 × 10 25 s −1 −1.1 × 10 26 s −1 , depending on the illumination conditions. This is slightly higher than the observed total production rate of 4×10 25 s −1 for H 2 O in August 2014 as reported by Gulkis et al (2015). We note that we estimate the total production rate of 67P which only gives an upper limit for the H 2 O production rate.…”

“…BATS-R-US produces these higher velocities on both the day and night side of the coma. The measured expansion velocity, reported by Gulkis et al (2015) of 0.68 km s −1 are somewhat lower than the BATS-R-US velocities computed for the day side and show better agreement with AMPS.…”

“…8 we can look at a direct comparison between the kinetic and hydrodynamic solutions in terms of number density, velocity, and pressure. The panels on the left hand side in both figures Gulkis et al (2015). Both methods produce asymmetric number density and velocity profiles with higher abundances and velocities on the hemisphere pointed towards the Sun.…”

“…It has been shown that comet 67P/Churyumov-Gerasimenko (67P) was active before Rosetta's rendezvous in August 2014 at a heliocentric distance of 3.75 AU as reported by Gulkis et al (2015). A major goal of the Rosetta mission is to find out how the gas release in comets works and how much of the surface area contributes to the observed activity.…”