Cometary dust provides a unique window on dust growth mechanisms during the onset of planet formation. Measurements by the Rosetta spacecraft show that the dust in the coma of comet 67P/Churyumov-Gerasimenko has a granular structure at size scales from sub-µm up to several hundreds of µm, indicating hierarchical growth took place across these size scales. However, these dust particles may have been modified during their collection by the spacecraft instruments. Here we present the results of laboratory experiments that simulate the impact of dust on the collection surfaces of COSIMA and MIDAS, instruments onboard the Rosetta spacecraft. We map the size and structure of the footprints left by the dust particles as a function of their initial size (up to several hundred µm) and velocity (up to 6 m s −1 ). We find that in most collisions, only part of the dust particle is left on the target; velocity is the main driver of the appearance of these deposits. A boundary between sticking/bouncing and fragmentation as an outcome of the particle-target collision is found at v ∼ 2 m s −1 . For velocities below this value, particles either stick and leave a single deposit on the target plate, or bounce, leaving a shallow footprint of monomers. At velocities > 2 m s −1 and sizes > 80 µm, particles fragment upon collision, transferring up to 50 per cent of their mass in a rubble-pile-like deposit on the target plate. The amount of mass transferred increases with the impact velocity. The morphologies of the deposits are qualitatively similar to those found by the COSIMA instrument.

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The structure of cometary dust is a tracer of growth processes in the formation of planetesimals. Instrumentation on board the Rosetta mission to comet 67P/Churyumov-Gerasimenko captured dust particles and analysed them in situ. However, these deposits are a product of a collision within the instrument. We conducted laboratory experiments with cometary dust analogues, simulating the collection process by Rosetta instruments (specifically COSIMA, MIDAS). In Paper I we reported that velocity is a key driver in determining the appearance of deposits. Here in Paper II we use materials with different monomer sizes, and study the effect of tensile strength on the appearance of deposits. We find that mass transfer efficiency increases from ∼ 1 up to ∼ 10% with increasing monomer diameter from 0.3 µm to 1.5 µm (i.e. tensile strength decreasing from ∼ 12 to ∼ 3 kPa), and velocities increasing from 0.5 to 6 m s −1 . Also, the relative abundance of small fragments after impact is higher for material with higher tensile strength. The degeneracy between the effects of velocity and material strength may be lifted by performing a closer study of the deposits. This experimental method makes it possible to estimate the mass transfer efficiency in the COSIMA instrument. Extrapolating these results implies that more than half of the dust collected during the Rosetta mission has not been imaged. We analysed two COSIMA targets containing deposits from single collisions. The collision that occurred closest to perihelion passage led to more small fragments on the target.

Accurate measurement of steam quality and enthalpy delivery rate at the wellhead is required for efficient operation and reliable evaluation of enhanced recovery projects that utilize steam injection. Steam distribution through manifolds and tees can lead to uneven splitting and a wide variation of steam quality and enthalpy delivery rate for different wells fed from the same boiler. A field-grade densitometer, which is based on the principle of thermal neutron transmission, has been developed and tested for measurement of steam quality at the wellhead. The meter is non-intrusive, portable, robust, easy to operate, safe for field use and accurate. By combining the meter with a flow measuring device, such as a flow nozzle, accurate measurements of steam quality, mass flow rate and enthalpy delivery rate at the wellhead are possible. This paper describes the densitometer's principle of operation and results from recent calibration tests conducted over a wide range of field conditions.

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