Deep Impact: Working Properties for the Target Nucleus – Comet 9P/Tempel 1

In 1998, Comet 9P/Tempel 1 was chosen as the target of the Deep Impact mission (A’Hearn, M. F., Belton, M. J. S., and Delamere, A., Space Sci. Rev., 2005) even though very little was known about its physical properties. Efforts were immediately begun to improve this situation by the Deep Impact Science Team leading to the founding of a worldwide observing campaign (Meech et al., Space Sci. Rev., 2005a). This campaign has already produced a great deal of information on the global properties of the comet’s nucleus (summarized in Table I) that is vital to the planning and the assessment of the chances of success at the impact and encounter. Since the mission was begun the successful encounters of the Deep Space 1 spacecraft at Comet 19P/Borrelly and the Stardust spacecraft at Comet 81P/Wild 2 have occurred yielding new information on the state of the nuclei of these two comets. This information, together with earlier results on the nucleus of comet 1P/Halley from the European Space Agency’s Giotto, the Soviet Vega mission, and various ground-based observational and theoretical studies, is used as a basis for conjectures on the morphological, geological, mechanical, and compositional properties of the surface and subsurface that Deep Impact may find at 9P/Tempel 1. We adopt the following working values (circa December 2004) for the nucleus parameters of prime importance to Deep Impact as follows: mean effective radius = 3.25± 0.2 km, shape – irregular triaxial ellipsoid with a/b = 3.2± 0.4 and overall dimensions of ∼14.4 × 4.4 × 4.4 km, principal axis rotation with period = 41.85± 0.1 hr, pole directions (RA, Dec, J2000) = 46± 10, 73± 10 deg (Pole 1) or 287± 14, 16.5± 10 deg (Pole 2) (the two poles are photometrically, but not geometrically, equivalent), Kron-Cousins (V-R) color = 0.56± 0.02, V-band geometric albedo = 0.04± 0.01, R-band geometric albedo = 0.05± 0.01, R-band H(1,1,0) = 14.441± 0.067, and mass ∼7×10¹³ kg assuming a bulk density of 500 kg m⁻³. As these are working values, {i.e.}, based on preliminary analyses, it is expected that adjustments to their values may be made before encounter as improved estimates become available through further analysis of the large database being made available by the Deep Impact observing campaign. Given the parameters listed above the impact will occur in an environment where the local gravity is estimated at 0.027–0.04 cm s⁻² and the escape velocity between 1.4 and 2 m s⁻¹. For both of the rotation poles found here, the Deep Impact spacecraft on approach to encounter will find the rotation axis close to the plane of the sky (aspect angles 82.2 and 69.7 deg. for pole 1 and 2, respectively). However, until the rotation period estimate is substantially improved, it will remain uncertain whether the impactor will collide with the broadside or the ends of the nucleus.     

On the stabilization of ribose by silicate minerals

The RNA-world theory hypothesizes that early Earth life was based on the RNA molecule. However, the notion that ribose, the sugar in RNA, is unstable still casts a serious doubt over this theory. Recently, it has been found that the silicate-mediated formose reaction facilitates the stabilization of ribose. Using accurate quantum chemical calculations, we determined the relative stability of the silicate complexes of arabinose, lyxose, ribose, and xylose with the intent to determine which would form predominantly from a formose-like reaction. Five stereoisomers were investigated for each complex. The stereoisomers of 2:1 ribose-silicate are the more stable ones, to the extent that the least stable of these is even more stable than the most stable stereoisomer of the other 2:1 sugar-silicate complexes. Thus, thermodynamically, a formose-like reaction in the presence of silicate minerals should preferentially form the silicate complex of ribose over the silicate complex of arabinose, lyxose, and xylose.     

Transparency and confidence-building measures for space security

Transparency and confidence-building measures (TCBMs) are a set of tools designed to display, predict and discipline states’ behaviour with respect to maintaining the security of space. With intentional and unintentional threats to the peaceful use of space on the rise, there is a growing international consensus on the need for greater transparency in space-related activities as well as confidence-building measures to reduce the prospects of disruption to the ever-expanding role of space in our day-to-day lives. Terrestrial TCBMs can serve as a guide to understanding what political arrangements are possible in space, including certain precedents in the areas of arms control, non-proliferation and disarmament. At the same time, current and emerging challenges in space - including orbital space debris, risk of collisions, growing saturation of the radiofrequency spectrum, the crowding of satellites in geostationary (GEO) orbit and threat of purposeful disruption - need to be evaluated in the context of unilateral, bilateral, multilateral and private initiatives to increase space situational awareness and security. This paper describes and evaluates various prospective TCBMs alongside current proposals to advance safety and security in space, including the EU Draft Code of Conduct for Outer Space Activities. It offers specific recommendations, arguing that Europe is uniquely qualified to negotiate a 21st century TCBM architecture thanks to its history of diplomacy and ability to identify common ground among disparate parties. This will only happen, however, with a more defined institutional design and the EU’s emergence as a global civilian leader.     

Remarks on “A new non-specificity measure in evidence theory based on belief intervals”

Two types of uncertainty co-exist in the theory of evidence: discord and non-specificity. From 90s, many mathematical expressions have arisen to quantify these two parts in an evidence. An important aspect of each measure presented is the verification of a coherent set of properties. About non-specificity, so far only one measure verifies an important set of those properties. Very recently, a new measure of non-specificity based on belief intervals has been presented as an alternative measure that quantifies a similar set of properties (Yang et al., 2016). It is shown that the new measure really does not verify two of those important properties. Some errors have been found in their corresponding proofs in the original publication.     

Comets, Asteroids and Zodiacal Light as Seen by Iso

ISO performed a large variety of observing programmes on comets, asteroids and zodiacal light – covering about 1% of the archived observations – with a surprisingly rewarding scientific return. Outstanding results were related to the exceptionally bright comet Hale–Bopp and to ISO's capability to study in detail the water spectrum in a direct way. But many other results were broadly recognised: Discovery of new molecules in comets, the studies of crystalline silicates, the work on asteroid surface mineralogy, results from thermophysical studies of asteroids, a new determination of the asteroid number density in the main-belt and last but not least, the investigations on the spatial and spectral features of the zodiacal light.     

Space security through the transatlantic partnership

On 12–14 June 2011, a conference was convened in Prague entitled ”Space Security through the Transatlantic Partnership“, co-sponsored by the European Space Policy Institute (ESPI) and the Prague Security Studies Institute (PSSI). It was the first non-governmental transatlantic conference of its kind dedicated to this topic, attended by over 100 senior space policy officials and high-level representatives of multilateral institutions, NGOs, academia, and industry from Europe, the USA, and Japan. The overarching goal of the conference was to solicit and assess both converging and diverging views on the multifaceted subject of space security and to seek to establish an on-going “Track II” non-governmental process designed to assist with the crafting of a future architecture for the management of this key dimension of space policy on a trilateral, and eventually global, basis. This report summarizes the proceedings.     

Forging a closer Europe–Japan strategic partnership: The space dimension

This viewpoint explores how a strengthening of Europe–Japan cooperation in four categories of space-related activities (exploration and access to space; Earth observation and related applications; industry-to-industry cooperation; and space security) can contribute to the EU–Japan strategic partnership more broadly. It is argued that integrating key space portfolios into existing venues and agendas for bilateral consultations and decision-making has the potential to bolster the overarching objective of deepening further political, economic, commercial, societal and cultural relations.     

The use of remote sensing satellites for verification in international law

This paper examines the use of remote sensing satellites for verification in public international law. Verification always depends on the specific agreement or mission to be verified. There are no general framework rules: the means of verification and the verifying authorities vary from agreement to agreement and from mission to mission. Rapid technological development and the intensifying international cooperation have led to an increasing number of international verification missions. Whereas, in the past, verification was at the heart of intelligence and national services, the commercialization of the remote sensing industry and the information revolution have supported the creation of joint initiatives in this field. Traditionally, verification is associated with disarmament and arms control treaties, but the paper will underline that this is only one field of application for verification missions. It is important to note that there is no binding international regime specifically addressing such activity. The lack of legal certainty in this field also applies to the use of remotely sensed data as evidence in legal proceedings.