ISANDAL · Ice: Small and Near, Distant and Large. Understanding planet formation through observation of Solar-System minor bodies and extra-solar planets

Ice: Small and Near, Distant and Large. Understanding planet formation through observation of Solar-System minor bodies and extra-solar planets

The project iSANDAL, “Ice: Small and Near, Distant and Large. Understanding planet formation through observation of solar system minor bodies and extra-solar planets”, aimed to build up a picture of how planetary systems formed by tracing the small icy bodies left behind. In our solar system, this means comets, asteroids and Kuiper Belt objects (KBOs), i.e. icy bodies with orbits further away from the Sun than that of the main planets. These bodies represent the remaining building blocks left over from the time of planet formation, and the ices they contain (water ice and frozen volatile compounds such as CO and CO2) are relatively pristine samples from this era. The larger part of this project was to understand where the ice is within our solar system, and how pristine it is in various minor body populations (i.e. what processes may have altered it over billions of years). A second part of the project looked at the wider context of ice within solar systems in general, by tracing the distribution of cool extra-solar planets. This part made use of the ‘microlensing’ planet hunting technique, which is most sensitive to planets at a few astronomical units (AU – the distance between the Sun and the Earth) from their host star, and therefore preferentially finds icy planets beyond the snow line in these systems. The project was primarily based on astronomical observations using a variety of telescopes at the European Southern Observatory and robotic telescopes worldwide (especially the network operated by Las Cumbres Observatory). It applied various imaging / photometry techniques at visible and near infra-red wavelengths. In addition, the project supported the ESA Rosetta mission to comet 67P/Churyumov-Gerasimenko, and in turn took advantage of data from the OSIRIS camera system on board this spacecraft. The overall topic was split into different sub-projects throughout the four years of the iSANDAL IRG. The first subtopic involved the direct study of ice on the surfaces of the largest bodies at the edge of the observable solar system. In an unexpected twist, our observations revealed ice not on the surface, but in a system of rings around the large Centaur-class object Chariklo. This discovery (Bragas-Ribas et al., 2014, Nature) was the first ever observation of rings around a small body – previously it was thought that these were something that was only seem around the giant planets (most famously around Saturn, of course). In the study of comets, papers were published from the SEPPCoN survey, and on the bright comet ISON, which captured public attention as it plunged towards the Sun, but sadly failed to survive the encounter. The vast majority of the work on comets was focussed on one comet in particular, 67P/Churyumov-Gerasimenko, the target of the ESA Rosetta mission. Much of the past two years has been spent preparing for the mission, including setting up of a global team of observers to follow it from the ground. Predictions for its behaviour during the Rosetta mission, based on ground-based observations of previous orbits, were published in 2013 (Snodgrass et al, A&A). Another key aspect was the study of icy bodies in the asteroid belt, including the newly discovered population of so-called main belt comets (MBCs), i.e. small objects with orbits typical of asteroids, but which show recurrent development of a cometary coma and tail. The pace of discovery of MBCs has increased, and follow up observations on a number of odd objects (including an asteroid with multiple tails) were published (e.g. Hainaut et al 2014). The work on these objects also built up the necessary scientific background to prepare a proposal for a new space mission, which is proposed to visit the main-belt comet 133P/Elst-Pizarro in 2029. The final part of this project, the wider context of planets around other stars, saw the completion of a world-wide network of robotically controlled telescopes as part of the RoboNet consortium. The software to control these ran almost without any need to trouble-shoot in the 2nd part of the iSANDAL programme, and these telescopes have contributed a vast amount of data to the search for extrasolar planets via the microlensing method. A large number of papers on this work have been published by other consortium members; it is becoming clear that small and icy extrasolar planets are common. Based on the success of all of all areas of the iSANDAL project, the researcher has been successful in obtaining an advanced fellowship in the UK, to continue this work with a particular focus on comets. The project successfully described a large range of icy environments in our solar system, providing the ideal background to the exciting (and very detailed) data that is now coming from the ESA Rosetta mission. Contact details of researcher Dr. Colin Snodgrass Ernest Rutherford Research Fellow The Open University Milton Keynes, MK7 6AA United Kingdom Colin.snodgrass@open.ac.uk

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