Commission 51: Bioastronomy

published_or_final_versio

ESA F-Class Comet Interceptor: Trajectory design to intercept a yet-to-be-discovered comet

Comet Interceptor (Comet-I) was selected in June 2019 as the first ESA F-Class mission. In 2029+, Comet-I will hitch a ride to a Sun-Earth L2 quasi-halo orbit, as a co-passenger of ESA's M4 ARIEL mission. It will then remain idle at the L2 point until the right departure conditions are met to intercept a yet-to-be-discovered long period comet (or interstellar body). The fact that Comet-I target is thus unidentified becomes a key aspect of the trajectory and mission design. The paper first analyses the long period comet population and concludes that 2 to 3 feasible targets a year should be expected. Yet, Comet-I will only be able to access some of these, depending mostly on the angular distance between the Earth and the closest nodal point to the Earth's orbit radius. A preliminary analysis of the transfer trajectories has been performed to assess the trade-off between the accessible region and the transfer time for a given spacecraft design, including a fully chemical, a fully electric and a hybrid propulsion system. The different Earth escape options also play a paramount role to enhance Comet-I capability to reach possible long period comet targets. Particularly, Earth-leading intercept configurations have the potential to benefit the most from lunar swing-by departures. Finally, a preliminary Monte Carlo analysis shows that Comet-I has a 95–99% likelihood of successfully visit a pristine newly-discovered long period comet in less than 6 years of mission timespan

Early Inner Solar System Impactors: Physical Properties of Comet Nuclei and Dust Particles Revisited

During the epoch of early bombardment, terrestrial planets have been heavily impacted by cometary nuclei and cometary dust particles progressively injected in the interplanetary medium. Stardust and Deep Impact missions confirm that the nuclei are porous, loosely consolidated objects, with densities below 1,000 kg m−3, and that they often release small fragments of ices and dust. Recent numerical simulations of the light scattering properties of cometary dust particles indicate that they are highly porous, most likely fractal, and rich in absorbing organics compounds (with a mixture ratio of e.g. 33 to 60% in mass for comet Hale–Bopp). Taking into account the fact that porous structures survive more easily than compact ones during atmospheric entry, such results reinforce the scenario of the early terrestrial planets enrichment – in organics needed for life to originate – by comets

Giotto Spacecraft

International audienceThe Giotto spacecraft (Fig. 1), the first ESA (European Space Agency) interplanetary probe, was designed to flyby comet Halley. Launched on 2 July 1985 by an Ariane-1 rocket from Kourou, Giotto succeeded in approaching the cometary nucleus to within 600 km on 14 March 1986. Through its first accurate images of a nucleus and in situ studies of gases and dust particles within a coma, the mission has revealed the complexity of comets. Afterwards, the Giotto spacecraft was re-oriented in order to study comet Grigg-Skjellerup, which was flown by on 10 July 1992, at a nucleus distance in the 150–200 km range

Optical Polarimetry of Small Solar System Bodies: From Asteroids to Debris Disks

Astrophysics and Space Science Library, vol 460International audienceWe present a review on polarimetric properties of small Solar system bodies. The main results of polarimetric investigations of asteroids, comets, transneptunian objects and Centaurs are discussed focusing on recent findings. We also discuss the polarimetric observations of dust clouds in our Solar system

Laboratory Studies of Icy Regoliths in Relation to Observations of Minor Bodies in the Outer Solar System

International audienceObserving the properties of solar light scattered by TNOs is (up to now) the only way to obtain information on the physical properties of their surfaces. As such observations, performed near backscattering, become available, it is important to stress the significance of the phase angle and wavelength dependences of the linear polarization of the scattered light. At small phase angles, a narrow spike in brightness and a significantly negative polarization could be typical of icy regoliths, actually expected to be formed by alteration of icy bodies surfaces. Accurate experimental simulations of icy aggregates and regoliths formation that should take place with the ICAPS facility on board the ISS are presented, with emphasis on light scattering measurements providing a link between remote observations of TNOs and physical properties of their surfaces