Jens Biele

The landing(s) of Philae and inferences about comet surface mechanical properties

The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.

Polarization Lidar: Correction of instrumental effects.

An algorithm for correcting instrumental effects in polarization lidar studies is discussed. Cross-talk between the perpendicular and parallel polarization channels and imperfect polarization of the transmitted laser beam are taken into account. On the basis of the Mueller formalism it is shown that - with certain assumptions - the combined effects of imperfect polarization of the transmitted laser pulse, non-ideal properties of transmitter and receiver optics and cross-talk between parallel and perpendicular polarization channels can be described by a single parameter, which is essentially the overall system depolarization.

Philae's first days on the comet

On 12 November 2014, Philae landed on the surface of comet 67P/Churyumov-Gerasimenko (67P), making an almost 30-year dream a reality. The pioneering flybys of 1P/Halley in 1986 revealed that despite being made primarily of ice, it was covered in highly absorbing carbonrich molecules. What is their composition? When did they form, and through which chemical routes? Might they have constituted prebiotic molecules necessary for life? At a larger scale, what can one learn from comets that has relevance to the evolution of the solar system and planets? ![Figure][1] 12 NOVEMBER 2014: PHILAE LANDED ON THE NUCLEUS OF COMET 67P CREDIT: ESA/ROSETTA/MPS FOR OSIRIS TEAM MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA To address such questions, the Rosetta mission sought to perform a broad range of in-depth structural, physical, and chemical measurements from remote, in situ, and landed vantages. The candidate payload opened for a competitive selection included an instrumented Surface Science Platform (SSP). The initial two that were selected later merged into what is known as Philae, instrumented by 10 principal investigators selected by the SSP providers. The Philae platform and payloads were developed and operated by a highly integrated consortium of institutes, agencies, and industries. Philaes scientific objectives were to provide ground-truth information and complement remote measurements performed from the Rosetta orbiter ( Science 347 , 23 January 2015) and to offer a self-standing suite of in situ measurements never before performed on a comet. This issue presents a first set of results acquired aboard Philae in the first 63 hours after it separated from Rosetta, descended, initially touched down on the comet at the site known as Agilkia, and finally came to rest at the site known as Abydos. The release and descent happened as planned, precisely documented by imaging (Mottola et al. ), ranging (Kofman et al. ), thermal mapping (Spohn et al. ), and the evolution of the magnetic properties (Auster et al. ). The prospect of landing on such an alien body, at 515 million km from Earth and 3 astronomical units (AU) from the Sun, was far more challenging than imagined. The unexpected bounce at touchdown required a major reshuffling and adaptation of the first sequence of science operations. It also provided the opportunity for additional measurements, whereas the bouncing and traversing constrained the mechanical (Biele et al. ) and magnetic properties of the surface. ROLIS imagery at its highest resolution (1 cm per pixel) showed the surface of the comet near Agilkia to be dominated by the presence of granular material free of any dust deposits (Mottola et al. ). Regolith mobilization processes appear to be involved with the formation of these features. Once Philae came to rest at Abydos, the revised first science sequence began. CIVA panoramic images characterized the surrounding cometary material down to the millimeter scale and the attitude of Philae at rest (Bibring et al. ). The MUPUS package measured and constrained the thermal and mechanical properties of the near-surface material of the comet surface at Abydos (Spohn et al. ), indicating that the near-surface layers consist of a hard dust-rich sintered ice, possibly covered by a thin dust layer. The CONSERT bistatic radar provided an opportunity to investigate the comets internal structure (Kofman et al. ). The upper “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. The average permittivity provides ranges of the volumetric dust/ice ratio and the internal porosity. The dust component may be comparable, from the dielectric properties, to that of carbonaceous chondritic meteorites. COSAC and Ptolemy independently measured the composition of the volatile constituents of the grains lifted at touchdown and of the species outgassed at the final landing site (Goesmann et al. and Wright et al. ). The grains are primarily made of carbon-rich species in a complex suite of molecules, including precursors to some biomolecules and other compounds never before identified in comets. Taken together, these first measurements performed at the surface of 67P profoundly modify our view of comets. 67P is nonmagnetized on a scale of less than a meter, with its surface layers composed of both sintered ices, which are hard in nature, and fluffy grains and pebbles of organic materials, possible remnants from the era of comet formation itself. Although it remains to be seen whether these observations hold true for all comets, the discoveries made by Philae—including these initial results—will continue to shape our view of the history of the solar system. [1]: pending:yes

Experimental Investigations of the Comet Lander Philae Touchdown Dynamics

The comet lander Philae (as part of Europe’s Rosetta mission) is en route to its target, 67/P Churyumov-Gerasimenko. With landing operations coming up at the end of 2014, a partial retesting of the Philae lander’s touchdown system was carried out in spring of 2013. Intensive testing was performed as part of Philae’s design and verification program approximately 10 years ago. However, the new test series specifically addresses touchdown conditions that have been out of capability of the pendulum test facility used at those times. Thus, the follow-up tests focus on touchdown conditions such as asymmetric loads, effects from terrain undulation, and the effect of granular soil mechanics, which could not be studied sufficiently in the original tests. This paper provides insight into the touchdown system of the Philae lander, the characteristics of the used test facility, its weight offloading operating mode, and the specific application to a small-body landing test. The results of the study are presented and d...

Current status and scientific capabilities of the ROSETTA Lander payload

Abstract ESAs cornerstone mission “ROSETTA” to comet 46P/Wirtanen will bring a 100 kg Lander (provided by an international European consortium) with a scientific payload of about 27 kg to the surface of the comets nucleus. After a first scientific sequence it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and 2 AU). The Lander is an autonomous spacecraft, powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in-situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground reference data for Orbiter instruments. Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives. In this paper we present the current status of the instrumental development and the scientific capabilities of each of the experiments.

The Experiments Onboard the Rosetta Lander

As a part of ESA’s cornerstone mission “ROSETTA” to comet 46P/Wirtanen a 100 kg Lander will bring a scientific payload of almost 27 kg to the surface of the nucleus. After a first scientific sequence it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and 2 AU). Ten experiments with a number of sub-experiments are foreseen; this paper presents the current status of the Lander development and reviews the scientific capabilities of each of the experiments at a time when the Flight Model (FM) of the Lander is already delivered.

Clean In Situ Subsurface Exploration of Icy Environments in the Solar System

To assess the habitability of the icy environments in the solar system, for example, on Mars, Europa, and Enceladus, the scientific analysis of material embedded in or underneath their ice layers is very important. We consider self-steering robotic ice melting probes to be the best method to cleanly access these environments, that is, in compliance with planetary protection standards. The required technologies are currently developed and tested.

AIDA: Asteroid Impact and Deflection Assessment

The Asteroid Impact & Deflection Assessment (AIDA) mission is a kinetic impactor experiment to demonstrate asteroid impact hazard mitigation by deflecting an asteroid. AIDA is an international cooperation between NASA and ESA, consisting of two mission elements: the NASA Double Asteroid Redirection Test (DART) mission and the ESA Asteroid Impact Mission (AIM) rendezvous mission. The primary goals of AIDA are (i) to demonstrate the kinetic impact technique on a potentially hazardous near-Earth asteroid and (ii) to measure and characterize the deflection caused by the impact. The AIDA target will be the binary asteroid (65803) Didymos, with the deflection experiment to occur in September, 2022. The DART impact on the secondary member of the binary at ~7 km/s will alter the binary orbit period, which can be measured by Earth-based observatories. The AIM spacecraft will characterize the asteroid target and monitor results of the impact in situ at Didymos. AIDA will return fundamental new information on the mechanical response and impact cratering process at real asteroid scales, and consequently on the collisional evolution of asteroids with implications for planetary defence, human spaceflight, and near-Earth object science and resource utilization. AIDA will return unique information on an asteroids strength, surface physical properties and internal structure. Supporting Earth-based optical and radar observations, numerical simulation studies and laboratory experiments will be an integral part of AIDA.