Planetary Dynamics and Habitable Planet Formation In Binary Star Systems

Whether binaries can harbor potentially habitable planets depends on several factors including the physical properties and the orbital characteristics of the binary system. While the former determines the location of the habitable zone (HZ), the latter affects the dynamics of the material from which terrestrial planets are formed (i.e., planetesimals and planetary embryos), and drives the final architecture of the planets assembly. In order for a habitable planet to form in a binary star system, these two factors have to work in harmony. That is, the orbital dynamics of the two stars and their interactions with the planet-forming material have to allow terrestrial planet formation in the habitable zone, and ensure that the orbit of a potentially habitable planet will be stable for long times. We have organized this chapter with the same order in mind. We begin by presenting a general discussion on the motion of planets in binary stars and their stability. We then discuss the stability of terrestrial planets, and the formation of potentially habitable planets in a binary-planetary system.Comment: 56 pages, 29 figures, chapter to appear in the book: Planets in Binary Star Systems (Ed. N. Haghighipour, Springer publishing company

Derivation of quantitative management objectives for annual instream water temperatures in the Sabie River using a biological index

No Abstract. Water SA Vol. 31(4) 2005: 473-48

Solar system: Portrait of a suburban family

Nature, 446, pp. 273-274, http://dx.doi.org./10.1038/446273aInternational audienc

Comet 67P/Churyumov-Gerasimenko sheds dust coat accumulated over the past four years

International audienceComets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate1, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer2, 3. The presence of water-ice grains in periodic comets is now well established4, 5, 6. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates7, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion8, 9, 10. Micrometre-sized interplanetary dust particles collected in the Earth’s stratosphere and certain micrometeorites are assumed to be of cometary origin11, 12, 13. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface14. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids15. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices2, 3. At its previous recurrence (orbital period 6.5 years), the comet’s dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun14, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun4, 5