Core-accretion theory predicts that the formation of giant planets predominantly occurs at the dense mid-plane of the inner ∼50 AU of protoplanetary disks. However, due to observational limitation, this critical region remains to be the least charted area in protoplanetary disks. With its great sensitivity, ALMA recently started to image optically thin line emissions arisen from the mid-plane of the inner 50AU in nearby disks, which unlocks an exciting new path to directly constrain the physical properties of the giant planet formation zone through gas tracers. Here we present the first spatially resolved observations of the 13C18O J=3-2 line emission in the TW Hya disk. We show that this emission is optically thin even inside the CO mid-plane snowline. Combining it with the C18O J=3-2 images and the previously detected HD J=1-0 flux, we directly constrain the mid-plane temperature and optical depths of the CO gas and dust. We report a mid-plane CO snowline at 20.5 ± 1.3 AU, a mid-plane temperature distribution of 27+4−3×(R/20.5AU)-0.47+0.06−0.07 K, and a gas mass distribution of 13+8−5×(R/20.5AU)-0.9+0.4−0.3 g cm−2 between 5-20.5 AU in the TW Hya protoplanetary disk. We find a total gas/mm-sized dust mass ratio of 140 ± 40 in this region, suggesting that ∼2.4 earth mass of dust aggregates have grown to > cm sizes (and perhaps much larger).

Connecting the observed composition of exoplanets to their formation sites often involves comparing the atmospheric C/O ratio to a disk midplane model with a fixed chemical composition. In this scenario chemistry during the planet formation era is not considered. However, kinetic chemical evolution during the lifetime of the gaseous disk can change the relative abundances of volatile species, thus altering the C/O ratios of planetary building blocks. In our chemical evolition models we utilize a large network of gas-phase, grain-surface and gas-grain interaction reactions, thus providing a comprehensive treatment of chemistry. The results show that, if sufficient ionisation is present, then chemistry does alter the C/O ratios of gas and ice during the epoch of planet(esimal) formation. This modifies the picture of C/O ratios in disk midplanes defined simply by volatile ice lines in a midplane of fixed chemical composition. Chemical evolution thus needs to be addressed when predicting the makeup of planets and their atmospheres.

We study the orbital evolution of a three-planet system with masses in the super-Earth regime resulting from the action of tides on the planets induced by the central star which cause orbital circularization. We consider systems either in or near to a three-body commensurability for which adjacent pairs of planets are in a first-order commensurability. We develop a simple analytic solution, derived from a time averaged set of equations, that describes the expansion of the system away from strict commensurability as a function of time, once a state where relevant resonant angles undergo small amplitude librations has been attained. We perform numerical simulations that show the attainment of such resonant states focusing on the Kepler 60 system. The results of the simulations confirm many of the scalings predicted by the appropriate analytic solution. We go on to indicate how the results can be applied to put constraints on the amount of tidal dissipation that has occurred in the system. For example, if the system has been in a librating state since its formation, we find that its present period ratios imply an upper limit on the time average of 1/Q′, With Q′ being the tidal dissipation parameter. On the other hand if a librating state has not been attained, a lower upper bound applies.

The interaction between planetary formation and protostellar disks is among the most critical remaining pieces in the puzzle of solar system assembly. Leading theoretical models are constructed around two distinct scenarios: gravitational instabilities and core accretion. The physics of each applies to quite different epochs of formation, and exhibits complex dependencies on parameters like disk density and viscosity. Untangling the effects such processes have on the final planetary statistics necessitates direct observation of exoplanets in their primordial state, prior to orbital migration. Furthermore, detailed study of the environment, such as the way the planets shape the protostellar disk by driving accretion streams across disk gaps, will also constrain formation models. Aperture masking interferometry has demonstrated a unique ability to probe the gaps within stellar disks. It has twin advantages of a higher dynamic range at the diffraction limit (λ/D) than differential imaging, while at the same time giving very extensive UV coverage compared to long baseline interferometry.

We present detailed models of the edge-on protoplanetary disk ESO Hα 569 (SSTgbs J111110.7-764157) from resolved scattered light images from HST and a complete spectral energy distribution. Data was obtained as part of an HST campaign to catalogue edge-on disks around young stars in nearby star forming regions (HST program 12514, PI: Karl Stapelfeldt). We confirm that this object is an optically thick edge-on disk around a young star with an outer radius of 125 AU. Using full radiative transfer models, we probe the distribution of dust grains and overall shape of the disk (inclination, scale height, dust mass, maximum particle size, inner radius, flaring exponent and surface/volume density exponent).

Many planets have been detected so far but very few around nearby stars that could allow characterization of their atmosphere thanks to their proximity. There are known exoplanets around less than 8.3% of the FGK stars of the Solar neighborhood (d<20 pc) and the vast majority of them are giant planets. Within the ESA Cosmic Vision 2015-2025 plan, the scientific goal of the NEAT (Nearby Earth Astrometric Telescope) mission is to detect and characterize planetary systems around these nearby stars in an exhaustive way down to 1 Earth-mass in the habitable zone. This survey would provide the actual planetary masses, the full characterization of the orbits including their inclination, for all the components of the planetary system down to the Earth-mass limit. NEAT will continue the work performed by Hipparcos and Gaia by reaching a precision that is improved by two orders of magnitude on pointed targets compared to Gaia. We present the free-flyer concept that has been submitted to the 2010 ESA call for M3 missions with two satellites flying in formation 40m apart.

A persistent difficulty in terrestrial planet formation models is creating Mars analogs with the appropriate mass: Mars is typically an order of magnitude too large in simulations. Some recent work found that a small Mars can be created if the planetesimal disk from which the planets form has an outermost edge at 1.0 AU. However, that work and no previous work could produce a truncation of the planetesimal disk while also explaining the mass and structure of the asteroid belt. We show that gas-driven migration of Jupiter inward to 1.5 AU, before its subsequent outward migration, can truncate the disk and repopulate the asteroid belt. This dramatic migration history of Jupiter suggests that the dynamical behavior of our giant planets was more similar to that inferred for extra-solar planets than previously thought, as both have been characterised by substantial radial migration.

The concept of a Galactic Habitable Zone (GHZ) was introduced for the Milky Way galaxy a decade ago as an extension of the earlier concept of the Circumstellar Habitable Zone. In this work, we consider the extension of the concept of a GHZ to other types of galaxies by considering two elliptical galaxies as examples, M87 and M32. We argue that the defining feature of the GHZ is the probability of planet formation which has been assumed to depend on the metallicity. We have compared the metallicity distribution of nearby stars with the metallicity of stars with planets to document the correlation between metallicity and planet formation and to provide a comparison to other galaxies. Metallicity distribution, based on the [Fe/H] ratio to solar, of nearby stars peaks at [Fe/H]≈−0.2 dex, whereas the metallicity distribution of extrasolar planet host stars peaks at [Fe/H]≈+0.4 dex. We compare the metallicity distribution of extrasolar planet host stars with the metallicity distribution of the outer star clusters of M87 and M32. The metallicity distribution of stars in the outer regions of M87 peaks at [Fe/H]≈−0.2 dex and extends to [Fe/H]≈+0.4 dex, which seems favourable for planet formation. The metallicity distribution of stars in the outer regions of M32 peaks at [Fe/H]≈−0.2 dex and extends to a much lower [Fe/H]. Both elliptical galaxies met the criteria of a GHZ. In general, many galaxies should support habitable zones.

Although late stage gap formation reduces the surface density in the vicinity of protoplanets, simulations suggest gas may continue to leak through the protoplanets tidal barrier, replenishing the gas supply and allowing protoplanets to acquire masses comparable to or larger than that of Jupiter. Global gas depletion is a possible explanation for gaseous planets with lower masses in weak-line T-Tauri disks and ice giants in our own solar system, but it is unlikely to have stalled the growth of multiple systems around nearby stars that contain relatively low-mass, close-in planets along with more massive and longer period companions. Here, we suggest a potential solution. We show that supersonic infall of surrounding gas onto a protoplanet is only possible interior to both its Bondi and Roche radii. Although the initial Bondi radius is much smaller than its Roche radius, the former overtakes the latter during its growth. Thereafter, a positive pressure gradient is required to induce the gas to enter the Roche lobe of the protoplanet and flow is significantly reduced. We present the results of analysis and numerical simulations to show that the accretion rate increases rapidly with the ratio of the protoplanets Roche to Bondi radii. Based on these results we suggest that in regions with low geometric aspect ratios gas accretion is quenched, resulting in relatively low protoplanetary masses.

As of today more than 30 planetary systems have been discovered in binary stars. In all cases the configuration is circumstellar, where the planets orbit around one of the stars. The formation process of planets in binary stars is more difficult than around single stars due to the gravitational action of the companion. An overview of the research done in this field will be given. The dynamical influence that a secondary companion has on a circumstellar disk, and how this affects the planet formation process in this challenging environment will be summarized. Finally, new fully hydrodynamical simulations of protoplanets embedded in disks residing in a binary star will be presented. Applications with respect to the planet orbiting the primary in the system γ Cephei will be presented.

About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupiter – a giant planet orbiting within 0.1 AU of the central star. Since these stars are typically of the F/G spectral type, the orbits of any terrestrial planets in their habitable zones at ~1 AU should be dynamically stable. However, because hot-Jupiters are thought to have formed in the outer regions of a protoplanetary disc, and to have then migrated through the terrestrial planet zone to their final location, it is uncertain whether terrestrial planets can actually grow and be retained in these systems. In this paper we review attempts to answer this question. Initial speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, all concluded that hot-Jupiter systems should lack terrestrial planets. We show that this assumption may be incorrect, for when terrestrial planet formation and giant planet migration are simulated simultaneously, abundant solid material is predicted to remain from which terrestrial planet growth can resume.

Historically, there have been two main groups dealing with the investigation of extraterrestrial life and habitable worlds. The first is IAU Commission 51, composed of astronomers, physicists and engineers who focus on the search for extrasolar planets, formation and evolution of planetary systems, and the astronomical search for intelligent signals. The second group, the International Society for the Study of the Origin of Life (ISSOL), is composed largely of biologists and chemists focusing research on the biogenesis and evolution of life on Earth and in the solar system. There are now a variety of international organizations dedicated to this field, and this triennium has seen the beginnings of coordination and interaction between the groups through the Federation of Astrobiology Organizations, FAO.

The European Astrobiology Network Association (EANA) coordinates and promotes astrobiology in the 17 European countries that are member of the organization. Astrobiology includes the study of the origin, evolution and distribution of life in the Universe. It is a multi-disciplinary science that encompasses the disciplines of chemistry, biology, palaeontology, geology, atmospheric physics, planetary physics and stellar physics. The open questions to be addressed and the steps ahead in cosmochemistry, star and planet formation, the chemistry of life's origin, the study of bacterial life as a reference and the search for habitats and biosignatures beyond the Earth are presented.

As the number of large scale ground- and space-bound planet detection and imaging projects is growing, the need for theoretical guidance in order to optimize instrumental design is rapidly mounting. In an effort to provide this required framework, we present the results of Monte Carlo simulations of the formation of giant planets and compare them with the current population of exoplanets. Our models show that due to the severe current observational detection bias only a small percentage (3.6 %) of the potentially existing planets can be detected. Indeed, a large number of planetary embryos never grow enough to become giant planets giving raise to a large populations of bodies with masses smaller than ${\simeq} 5 M_{\hbox{\it \scriptsize jup}}$. In addition, this observational bias, coupled with the fact that systems enriched in heavy elements tend to form more massive planets, explains the currently observed correlation between stellar metallicity and likelihood to host planets. Finally, we show that the disk gas delivery rate during the late stages of formation actually determines the maximum planetary mass.

We present simulations which demonstrate to which extent mid-infrared images and millimeter maps can be used to trace the location of giant planets in circumstellar disks. The most promising approach is to look for characteristic signatures in circumstellar disks caused by the interaction of giant planets with the disk. Numerical simulations show that these signatures are usually in size much larger than the planet itself and thus much easier to detect. The particular result of the planet-disk-interaction depends on the evolutionary stage of the disk. Primary signatures of planets embedded in disks are gaps in the case of young disks and characteristic asymmetric density patterns in debris disks. Radiative transfer simulations predict that high spatial resolution observations performed with instruments/telescopes that will become available in the near future will allow to trace the formation and evolution of planets in protoplanetary and debris disks.

This paper presents recent results concerning the planet formation, planet migration, and the long term stability of planetary systems. Most stars are found in binary systems and binary companions can disrupt both planet formation and stability. We first consider the effects of outer binary companions on the late stages of terrestrial planet formation and show how planet formation depends on the binary periastron. We then consider migration mechanisms for giant planets. In this case, planet scattering produces the full range of orbital eccentricities, but is less effective in moving planets inward (decreasing their semi-major axes). Disk torques are effective at moving planets inward, but not at increasing the eccentricities. We explore a scenario in which disk torques act in concert with planet scattering to provide the full range of orbital elements observed in extrasolar planetary systems. Finally, we consider the longer term stability of Earth-like planets in binary systems; we find that nearly 50 percent of binaries allow for Earth-like planets to remain stable over the current (4.6 Gyr) age of our solar system.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html