Attraction between the atoms of a Bose–Einstein condensate renders it unstable to collapse, although a condensate with a limited number of atoms1 can be stabilized2 by confinement in an atom trap. However, beyond this number the condensate collapses3,4,5. Condensates constrained to one-dimensional motion with attractive interactions are predicted to form stable solitons, in which the attractive forces exactly compensate for wave-packet dispersion1. Here we report the formation of bright solitons of 7Li atoms in a quasi-one-dimensional optical trap, by magnetically tuning the interactions in a stable Bose–Einstein condensate from repulsive to attractive. The solitons are set in motion by offsetting the optical potential, and are observed to propagate in the potential for many oscillatory cycles without spreading. We observe a soliton train, containing many solitons; repulsive interactions between neighbouring solitons are inferred from their motion.

Formation and propagation of matter-wave soliton trains

Jupiter and Saturn formed in a few million years from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only approximately 100,000 years. Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration. The terrestrial planets finished accreting much later and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (1 AU is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 AU, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 AU; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 AU and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.

A low mass for Mars from Jupiter's early gas―driven migration

The formation of planetesimals, the kilometer-sized planetary precursors, is still a puzzling process. Considerable progress has been made over the past years in the physical description of the first stages of planetesimal formation, owing to extensive laboratory work. This review examines the experimental achievements and puts them into the context of the dust processes in protoplanetary disks. It has become clear that planetesimal formation starts with the growth of fractal dust aggregates, followed by compaction processes. As the dust-aggregate sizes increase, the mean collision velocity also increases, leading to the stalling of the growth and possibly to fragmentation, once the dust aggregates have reached decimeter sizes. A multitude of hypotheses for the further growth have been proposed, such as very sticky materials, secondary collision processes, enhanced growth at the snow line, or cumulative dust effects with gravitational instability. We will also critically review these ideas.

/pdf/the-growth-mechanisms-of-macroscopic-bodies-in-3gmwom4rl0.pdf

The Growth Mechanisms of Macroscopic Bodies in Protoplanetary Disks

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

/pdf/comet-81p-wild-2-under-a-microscope-4udr8g9spl.pdf

Comet 81P/Wild 2 under a microscope.

▪ Abstract Our understanding of the evolution of organic molecules, and their voyage from molecular clouds to the early solar system and Earth, has changed dramatically. Incorporating recent observ...

/pdf/organic-molecules-in-the-interstellar-medium-comets-and-14nzw41xt5.pdf

Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth

5. Surface Science

Terahertz time-domain spectroscopy of astrophysical ice analogs: A pilot study

In a recent paper Pendleton et al. (1998) present new spectra of embedded protostars which exhibit a broad absorption feature near 4.62 μm (2165 cm−1). In the literature this band is referred to as the “X(C≡N)” band. However Pendleton et al. (1998) cannot exclude the possibility of a different identification (such as an Si-H related compound) for which they claim the need of experimental data. To contribute to fulfill this request we present here new laboratory results on: (1) the formation of Si-H bonds induced by implantation of 30 keV H+, H2 and CH+ ions into silicon and (2) the production of SiH-containing refractory species by ion irradiation (60 keV Ar ions) of frozen dichlorosilane (SiCl2H2). The obtained results and others already available in the literature have been compared with astronomical observations. Even if we are aware that the sample we consider here is far from being complete, we suggest that it is possible to exclude that a refractory species containing Si-H groups can be responsible for the interstellar feature.

http://aa.springer.de/papers/8338001/2300292.pdf

Si-H bonds produced by ion implantation in silicon and frozen silanes

Planets and their moons are constantly subjected to irradiation from both their respective planetary magnetospheres and the solar wind. Energetic particles (electrons, protons and ions) in such radiation may induce complex chemistry within the icy mantles of such bodies, producing many organic compounds. Such processes can be simulated in laboratory experiments. In this report we present recent results from experiments exploring both molecular synthesis and the morphology of such ices.The morphology of any ice may be characterised by IR and Vacuum Ultra-Violet (VUV) spectroscopy. The latter is particularly useful for studying ices in which infrared inactive molecules like oxygen (O2) are common. We have shown that oxygen forms dimers in typical planetary ices and that, in contrast to previous analysis, many of the chemical reactions within the ice involve such dimer (and larger cluster) chemistry. We also present the results of a series of experiments that explore electron, proton and ion irradiation on Solar System relevant ices such as carbon dioxide (CO2) at different temperatures. Infrared spectra recorded before and after irradiation are used to identify and quantify molecules formed in such irradiation, e. g. ozone. These experiments show that the morphology of the ice plays a critical role in the chemistry.

/pdf/electron-proton-and-ion-induced-molecular-synthesis-and-vuv-4iznbhisvz.pdf

Maria Elisabetta Palumbo

Papers

5. Surface Science

Terahertz time-domain spectroscopy of astrophysical ice analogs: A pilot study

Si-H bonds produced by ion implantation in silicon and frozen silanes

Electron, proton and ion induced molecular synthesis and VUV spectroscopy of interstellar molecules in the ice phase

Sulfur and carbon bearing molecules on the Galilean moons