Spatially resolved evolution of the local H₂O production rates of comet 67P/Churyumov-Gerasimenko from the MIRO instrument on Rosetta

Abstract

Aims. Using spectroscopic and continuum data measured by the MIRO instrument on board Rosetta of comet 67P/Churyumov-Gerasimenko, it is possible to derive and track the change in the water production rate, to learn how the outgassing evolves with heliocentric distance. The MIRO data are well suited to investigate the evolution of 67P, in unprecedented spatial and temporal detail. Methods. To obtain estimates of the local effective Haser production rates we developed an efficient and reliable retrieval approach with precalculated lookup tables. We employed line area ratios (H 16 2 O/H 18 2 O) from pure nadir observations as the key variable, along with the Doppler shift velocity, and continuum temperature. This method was applied to the MIRO data from August 2014 until April 2016. Perihelion occurred on August 13, 2015 when the comet was 1.24 AU from the Sun. Results. During the perihelion approach, the water production rates increased by an order of magnitude, and from the observations, the derived maximum for a single observation on August 29, 2015 is (1.42 ± 0.51) × 10 28. Modeling the data indicates that there is an offset in the peak outgassing, occurring 34 ± 10 days after perihelion. During the pre-perihelion phase, the production rate changes with heliocentric distance as r −3.8±0.2 h ; during post-perihelion, the dependence is r −4.3±0.2 h. The comet is calculated to have lost 0.12 ± 0.06 % of its mass during the perihelion passage, considering only water ice sublimation. Additionally, this method provides well sampled data to determine the spatial distribution of outgassing versus heliocentric distance. The time evolution is definitely not uniform across the surface. Pre-and post-perihelion, the surface temperature on the southern hemisphere changes rapidly, as does the sublimation rate with an exponent of ∼−6. There is a strong latitudinal dependence on the r h exponent with significant variation between northern and southern hemispheres, and so the average over the comet surface may only be of limited importance. We present more detailed regional variation in the outgassing, demonstrating that the highest derived production rates originate from the Wosret, Neith and Bes regions during perihelion.

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

“…Beyond the early phase of the mission, continuum temperatures from MIRO covering August 2014 to April 2016 are given in Marshall et al (2017). The observed sub-surface temperatures vary from 70 K to 255 K, with the highest temperatures recorded around perihelion when 67P was at 1.24 au from the Sun.…”

The sublimative torques of Jupiter Family Comets and mass wasting events on their nuclei

“…Relatedly, the smooth waist terrain of comet 103P/Hartley 2 is a highly active (A'Hearn et al 2011;Feaga et al 2017), shallowly sloping terrain far from a steeply sloping surface . Similarly, the Imhotep terrain of comet 67P/Churyumov-Gerasimenko is a smooth, flat terrain that is also active (e.g., Marshall et al 2017, El-Maarry et al 2017). However, both of these terrains are likely formed from the ballistic deposition of icerich materials ejected from other parts of the nucleus (A'Hearn et al 2011;Keller et al 2017;Lai et al 2017), and are therefore symptomatic of activity elsewhere on the nucleus.…”

Ion Velocity and Electron Temperature Inside and Around the Diamagnetic Cavity of Comet 67P

“…However, Ip and Axford (1987) and Cravens (1986Cravens ( , 1987 found this to be insufficient to explain the extent of the cavity observed at Halley Journal of Geophysical Research: Space Physics 10.1029/2018JA025542 and February 2016 considered in this paper, published measurements are scarce. Marshall et al (2017) used a range of 400 m/s to 1 km/s, with a preferred value of 700 m/s, to obtain local effective production rates of H 2 O from H 16 2 O∕H 18 2 O line area ratios obtained by Microwave Instrument on the Rosetta Orbiter for the entire period from August 2014 to April 2016, though no more specific values are given from within this period. Heritier et al (2017) used a one-dimensional model for the neutral gas based on an adiabatic fluid expansion around the nucleus driven by inner boundary conditions on gas outflow velocity from Huebner and Markiewicz (2000) and temperature from the thermophysical model of Davidsson and Gutiérrez (2005) to find terminal velocities of about 800 m/s.…”