Detection of structure in asteroid analogue materials and Titan’s regolith by a landing spacecraft

Abstract

We compare measurements made by two impact penetrometers of different sizes and with different tip shapes to further understand penetrometer design for performing pentrometry on an asteroid. To this end we re-visit the interpretation of data from the Huygens' penetrometer, ACC-E, that impacted Titan's surface. In addition we investigate the potential of a spacecraft fitted with a penetrometer to bounce using a test rig, built at The Open University (UK).Analysis of ACC-E laboratory data, obtained from impacts into ∼4 mm diameter gravel, was found to produce an unusual decrease in resistance with depth (force-depth gradient) which was also seen in the Huygens' ACC-E data from Titan and originally interpreted as a wet or moist sand. The downward trend could also be reproduced in a hybrid Discrete Element Model (DEM) if it was assumed that the near surface particles are more readily * Corresponding author mobilised than those deeper in the target. With regard to penetrometer design penetration resistance was found to be sensitive to the ratio of particle to tip diameter. A clear trend was observed with a conical tip penetrometer, X-PEN, of decreasing force-depth gradients with increasing particle sizes most likely due to a transformation from a bulk displacement of material by the penetrating tip to more local interactions. ACC-E, which has a hemispherical tip, was found to produce a wider range of force-depth gradients than X-PEN, which had a conical tip, possibly due to difficulties dislodging jammed particles. Both penetrometers were able to determine particle diameter and mass after post-processing of the data.Laboratory simulations of landings with the test rig suggest that a large impact penetrometer under certain circumstances could absorb a significant amount of the elastic energy of the spacecraft possibly aiding landing. Alternatively a small impact penetrometer would allow the spacecraft to bounce freely off the surface to make a measurement at another location.

Study of Chemical Processes Initiated by Electrical Discharge in Titan-Related Atmosphere at Laboratory Temperature and Pressure

“…26 Lightning, whcih is well-known in Earth's atmosphere, was confirmed in more planetary atmospheres. 21,27,28,35 While the occurrence of lightning on Venus is still a controversial question, 36,37 there is clear evidence of lightning in the atmospheres of the gas giants like Jupiter, Saturn, 38 and Uranus. 39−41 Lightning is also believed to take place at Neptune.…”

“…28,34 Up to now, nearly all laboratory studies of Titan's atmosphere and the discharge initiated processes have been carried out at ambient temperature and pressure that were not fully reflecting Titan's real surface conditions. 27,50 The optical emission spectroscopy was broadly used for the determination of atomic and diatomic radiating species 51−53 to obtain the insight into molecular dissociation and formation of the simplest molecules like the CN radical. 54,55 A couple of laboratory studies were devoted to optical emission spectroscopic measurements of DC flowing plasmas in Pyrex/ Quartz tubes or stainless steel reactors 56 at pressures of about 1 kPa.…”

“…It is assumed that this rain, which is predominantly methane and possibly ethane, creates lakes on Titan. Thus, the methane cycle on Titan is similar to the cycle of water on Earth. − However, due to Titan’s low temperature (about 95 K at the surface), most of its water is presented as ice in the crust and mantle, acting similarly to the bedrock on Earth. Titan’s atmosphere is of particular interest because of a small planetary mass with a surface pressure 1.5 times higher than on Earth but with an inferred loss rate due to its lower gravity. − …”

“…It is assumed that the electrical discharge phenomena can play an important role in the atmospheric chemistry at lower altitudes . Lightning, whcih is well-known in Earth’s atmosphere, was confirmed in more planetary atmospheres. ,,, While the occurrence of lightning on Venus is still a controversial question, , there is clear evidence of lightning in the atmospheres of the gas giants like Jupiter, Saturn, and Uranus. − Lightning is also believed to take place at Neptune. , Moreover, it was pointed out very recently that the lightning activity in Jupiter’s atmosphere is significantly higher than was expected, and thus the same situation can be also assumed in other atmospheres . Besides the classical lightning phenomena, transient lightning events like sprites, jets, and elves were recently also confirmed in the atmospheres of Venus, Mars, and Jupiter …”

“…The planetary scale chemical processes initiated by electrical discharge can be simulated by laboratory experiments using various discharges: corona and DBD conditions are similar to the St. Elmo’s fire, spark and arc discharges are related to the lightning, and corona and glow discharge conditions are similar to the conditions in the aurora borealis. , Up to now, nearly all laboratory studies of Titan’s atmosphere and the discharge initiated processes have been carried out at ambient temperature and pressure that were not fully reflecting Titan’s real surface conditions. , The optical emission spectroscopy was broadly used for the determination of atomic and diatomic radiating species − to obtain the insight into molecular dissociation and formation of the simplest molecules like the CN radical. , A couple of laboratory studies were devoted to optical emission spectroscopic measurements of DC flowing plasmas in Pyrex/Quartz tubes or stainless steel reactors at pressures of about 1 kPa. The detailed numeric models describing formation of simple species like CN were designed and compared with the experimental data .…”