Silence on Shangri-La: attenuation of Huygens acoustic signals suggests surface volatiles

Objective: Characterize and understand acoustic instrument performance on the surface of Titan. Methods: The Huygens probe measured the speed of sound in Titan's atmosphere with a 1 MHz pulse time-of-flight transducer pair near the bottom of the vehicle. We examine the fraction of pulses correctly received as af unction of time. Results: This system returned good data from about 11 km altitude, where the atmosphere became thick enough to effectively transmit the sound, down to the surface just before landing: these data have been analyzed previously. After an initial transient at landing, the instrument operated nominally for about 10 min, recording pulses much as during descent. The fraction of pulses detected then declined and the transmitted sound ceased to be detected altogether, despite no indication of instrument or probe configuration changes. Conclusions: The most likely explanation appears to be absorption of the signal by polyatomic gases with relaxation losses at the instrument frequency, such as ethane, acetylene and carbon dioxide. These vapors, detected independently by the GCMS instrument, were evolved from the surface material by the warmth leaking from the probe, and confirm the nature of the surface materials as ‘damp’ with a cocktail of volatile compounds. Some suggestions for future missions are considered. Practice implications: None

Penetrometry of granular and moist planetary surface materials: Application to the Huygens landing site on Titan

The Huygens probe landed on the then unknown surface of Titan in January 2005. A small, protruding penetrometer, part of the Surface Science Package (SSP), was pushed into the surface material measuring the mechanical resistance of the ground as the probe impacted the landing site. We present laboratory penetrometry into room temperature surface analogue materials using a replica penetrometer to investigate further the nature of Titan's surface and examine the sensor's capabilities. The results are then compared to the flight instrument's signature and suggest the Titan surface substrate material consists of sand-sized particles with a mean grain size ~2 mm. A possible thin 7 mm coating with mechanical properties similar to terrestrial snow may overlie this substrate, although due to the limited data we are unable to detect any further layering or grading within the near-surface material. The unusual weakening with depth of the signature returned from Titan has, to date, only been reproduced using a damp sand target that becomes progressively wetter with depth, and supports the suggestion that the surface may consist of a damp and cohesive material with interstitial liquid contained between its grains. Comparison with terrestrial analogues highlights the unusual nature of the landing site material

Mars Phobos and Deimos Survey (M-PADS) – A Martian Moons Orbiter and Phobos Lander

We describe a Mars 'Micro Mission' for detailed study of the martian satellites Phobos and Deimos. The mission involves two ~330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988-89) failed to realise its full potential. Many questions remain concerning the moons' origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA's Aurora programme

In situ multi-frequency measurements of magnetic susceptibility as an indicator of planetary regolith maturity

Space weathering is now generally accepted to modify the optical and magnetic properties of airless planetary regoliths such as those on the Moon and Mercury. Under micrometeorite and ion bombardment, ferrous iron in such surfaces is reduced to metallic iron spheres, found in amorphous coatings on almost all exposed regolith grains. The size and number distribution of these particles and their location in the regolith all determine the nature and extent of the optical and magnetic changes. These parameters in turn reflect the formation mechanisms, temperatures, and durations involved in the evolution of the regolith. Studying them in situ is of intrinsic value to understanding the weathering process, and useful for determining the maturity of the regolith and providing supporting data for interpreting remotely sensed mineralogy. Fine-grained metallic iron has a number of properties that make it amenable to magnetic techniques, of which magnetic susceptibility is the simplest and most robust. The magnetic properties of the lunar regolith and laboratory regolith analogues are therefore reviewed and the theoretical basis for the frequency dependence of magnetic susceptibility presented. Proposed here is then an instrument concept using multi-frequency measurements of magnetic susceptibility to confirm the presence of fine grained magnetic material and attempt to infer its quantity and size distribution. Such an instrument would be invaluable on a future mission to an asteroid, the Moon, Mercury or other airless rocky Solar System body

On the application of magnetic methods for the characterisation of space weathering products

Space weathering is now commonly accepted to modify the optical and magnetic properties of airless body regoliths throughout the Solar System. Although the precise formation processes are not well understood, the presence of ubiquitous sub-microscopic metallic iron (SMFe) grains in lunar soils and corresponding spectral analyses have explained both the unique optical and magnetic properties of such soils. More recently, a variety of ion irradiation, laser melting and vaporisation and impact experiments have been shown to reproduce these effects in the laboratory. Such experiments are crucial to the study of the formation of SMFe under controlled conditions. To date, more emphasis has been placed on optical analyses of laboratory samples, as these address directly the mineralogical interpretation of remote sensing data. However, the magnetic analyses performed on the Apollo and Luna samples have provided useful qualitative and quantitative evaluation of regolith metallic iron content. These techniques are reviewed here, demonstrated on pulsed laser irradiated olivine powder, and their utility for determining the quantity and size distribution of this metallic iron discussed. Ferromagnetic resonance, multi- frequency magnetic susceptibility, vibrating sample magnetometry and thermomagnetic measurements were carried out. Each showed trends expected for the conversion of paramagnetic Fe2+ in olivine to fine-grained Fe0, with some grains in the superparamagnetic size range. Although evidence for super- paramagnetic iron was found, the quantity of sub-microscopic metallic iron produced in these experiments proved insufficient to make conclusive measurements of either the quantity or size distribution of this iron. Improvements to both the experimental and analytical procedures are discussed to better enable such measurements in the future

Overview of the coordinated ground-based observations of Titan during the Huygens mission

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Satumian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental imnortance for the interpretatinn of results from the Huygens mission

Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks

无线传感器网络，作为全球未来十大技术之一，集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术，可实时感知、采集、处理、传输网络分布区域内的各种信息数据，在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议，并针对大规模的无线传感器网络设计了一种树状路由协议，它根据节点地址信息来形成路由，从而简化了复杂繁冗的路由表查找和维护，节省了不必要的开销，提高了路由效率，实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR（AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位：工学硕士院系专业：信息科学与技术学院通信工程系_通信与信息系统学号：2332007115216

The detection of extra-terrestrial life and the consequences for science and society

Astronomers are now able to detect planets orbiting stars other than the Sun where life may exist, and living generations could see the signatures of extra-terrestrial life being detected. Should it turn out that we are not alone in the Universe, it will fundamentally affect how humanity understands itself—and we need to be prepared for the consequences. A Discussion Meeting held at the Royal Society in London, 6–9 Carlton House Terrace, on 25–26 January 2010, addressed not only the scientific but also the societal agenda, with presentations covering a large diversity of topics

Body signals

As a university admissions officer, I am painfully aware of the imbalance between the sexes in physics, and of the need for the physics profession and industry to attract more women into its ranks. It did not therefore surprise me to read that only 10% of respondents in your recent salary survey were women

Interaction of solar flare X-rays with the atmosphere of Titan

During solar flares an intense flux of X-rays is emitted into space. When it reaches Saturn's orbit, it is still strong enough to significantly disturb Titan's dense atmosphere. The main effect is to ionize the neutral component of the atmosphere and to increase, therefore, the electron and ion density at altitudes of 400-900 km. Especially near a maximum of the solar cycle, when flare activity is high, the average plasma density can, for long intervals, remain at a level of a few tens of particles per cm(3). As a result, the atmospheric photochemistry will be affected, but also an increase of production rate of small haze particles might be expected. Ionized atoms are usually excited; when they relax to the ground level in the process of resonant fluorescence, Titan's albedo at specific wavelengths increases. It is estimated that at Earth orbit the flux of photons emitted from Titan in the 3 KeV argon line during a strong X1-type Rare is equal to 1.6 x 10(-20) J m(-2) s(-1) for 10% Ar abundance in Titan's atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved