caa a22 4500 445863374 CHVBK 20180317145450.0 cr unu---uuuuu 170323e20111001xx s 000 0 eng 10.1007/s10569-011-9346-2 doi (NATIONALLICENCE)springer-10.1007/s10569-011-9346-2 Thebault P. LESIA, Observatoire de Paris, 92195, Meudon Principal Cedex, France aut Against all odds? Forming the planet of the HD 196885 binary [Elektronische Daten] [P. Thebault] HD 196885 Ab is the most "extreme” planet-in-a-binary discovered to date, whose orbit places it at the limit for orbital stability. The presence of a planet in such a highly perturbed region poses a clear challenge to planet-formation scenarios. We investigate this issue by focusing on the planet-formation stage that is arguably the most sensitive to binary perturbations: the mutual accretion of kilometre-sized planetesimals. To this effect we numerically estimate the impact velocities dv amongst a population of circumprimary planetesimals. We find that most of the circumprimary disc is strongly hostile to planetesimal accretion, especially the region around 2.6 AU (the planet's location) where binary perturbations induce planetesimal-shattering dv of more than 1 kms−1. Possible solutions to the paradox of having a planet in such accretion-hostile regions are (1) that initial planetesimals were very big, at least 250km (2) that the binary had an initial orbit at least twice the present one, and was later compacted due to early stellar encounters (3) that planetesimals did not grow by mutual impacts but by sweeping of dust (the "snowball” growth mode identified by Xie etal., in Astrophys J 724:1153, 2010b), or (4) that HD 196885 Ab was formed not by core-accretion but by the concurrent disc instability mechanism. All of these 4 scenarios remain however highly conjectural. Springer Science+Business Media B.V., 2011 Planetary systems nationallicence Binary stars nationallicence HD 196885 nationallicence Planet formation scenario nationallicence Planetesimal accretion nationallicence Celestial Mechanics and Dynamical Astronomy Springer Netherlands 111/1-2(2011-10-01), 29-49 0923-2958 111:1-2<29 2011 111 10569 https://doi.org/10.1007/s10569-011-9346-2 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10569-011-9346-2 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Thebault P. LESIA, Observatoire de Paris, 92195, Meudon Principal Cedex, France aut NATIONALLICENCE 773 0- Celestial Mechanics and Dynamical Astronomy Springer Netherlands 111/1-2(2011-10-01), 29-49 0923-2958 111:1-2<29 2011 111 10569 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer