Many hot Jupiters where found within the last 20 years which makes it difficult to believe that in the zone outside of such a system terrestrial planets may orbit in habitable zones. Systems with only one gas giant are also in the long list of discovered extrasolar planets, but our interest was orientated versus systems with more gas giants. Several ones are known but of special interest seems the recently discovered four-planets system HD 141399 (Voigt et al,2014).
In this article they carefully describe the method of determining the orbital elements of the planets and in addition checked their stability which seems to be garanteed because of the almost circular orbits of the four planets even when larger masses involved. Our aim was to find out whether terrestrial planets could be formed therein in the habitable zone around that late K type star where we also took care of the possible water content with respect of their location in the ring between planets c and d.
Collisions between celestial bodies to finally form planets should be treated using SPH codes
which take care of fragmentation and loss of water during such an event – some examples are shown.