Search Publications
Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula
Blum, J.; Lacerda, P.; Lorek, S.
Context. Comet formation by gravitational instability requires aggregates that trigger the streaming instability and cluster in pebble-clouds. These aggregates form as mixtures of dust and ice from (sub-)micrometre-sized dust and ice grains via coagulation in the solar nebula. Aim. We investigate the growth of aggregates from (sub-)micrometre-size…
Thermal inertia and roughness of the nucleus of comet 67P/Churyumov-Gerasimenko from MIRO and VIRTIS observations
Jorda, L.; Kührt, E.; Mottola, S. +17 more
Aims: Using data from the Rosetta mission to comet 67P/Churyumov-Gerasimenko, we evaluate the physical properties of the surface and subsurface of the nucleus and derive estimates for the thermal inertia (TI) and roughness in several regions on the largest lobe of the nucleus.
Methods: We have developed a thermal model to compute the tem…
Plasma source and loss at comet 67P during the Rosetta mission
Altwegg, K.; Carr, C.; Henri, P. +10 more
Context. The Rosetta spacecraft provided us with a unique opportunity to study comet 67P/Churyumov-Gerasimenko (67P) from a close perspective and over a 2-yr time period. Comet 67P is a weakly active comet. It was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, e…
Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs
Jorda, L.; Lara, L. M.; Bertaux, J. -L. +52 more
We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The …
The infant bow shock: a new frontier at a weak activity comet
Simon Wedlund, Cyril; Nilsson, Hans; Goetz, Charlotte +6 more
The bow shock is the first boundary the solar wind encounters as it approaches planets or comets. The Rosetta spacecraft was able to observe the formation of a bow shock by following comet 67P/Churyumov-Gerasimenko toward the Sun, through perihelion, and back outward again. The spacecraft crossed the newly formed bow shock several times during two…
Size of a plasma cloud matters. The polarisation electric field of a small-scale comet ionosphere
Gunell, H.; Behar, E.; Nilsson, H. +7 more
Context. The cometary ionosphere is immersed in fast flowing solar wind. A polarisation electric field may arise for comets much smaller than the gyroradius of pickup ions because ions and electrons respond differently to the solar wind electric field.
Aims: A situation similar to that found at a low activity comet has been modelled for bariu…
Linking interstellar and cometary O2: a deep search for 16O18O in the solar-type protostar IRAS 16293-2422
Altwegg, K.; Codella, C.; Bieler, A. +15 more
Recent measurements carried out at comet 67P/Churyumov-Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2, is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O
Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period
Behar, E.; Nilsson, H.; Goetz, C. +4 more
Aims: Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma. We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in the terminator plane.
Methods: We analysed in situ ion and magnetic field measur…
Cold electrons at comet 67P/Churyumov-Gerasimenko
Henri, P.; Rubin, M.; Vigren, E. +4 more
Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies 10 eV. In an active comet coma, the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (a few hundred kelvin). How coolin…
Thermal fracturing on comets. Applications to 67P/Churyumov-Gerasimenko
Jorda, L.; Kührt, E.; Groussin, O. +12 more
We simulate the stresses induced by temperature changes in a putative hard layer near the surface of comet 67P/Churyumov-Gerasimenko with a thermo-viscoelastic model. Such a layer could be formed by the recondensation or sintering of water ice (and dust grains), as suggested by laboratory experiments and computer simulations, and would explain the…