http://www.astro.sunysb.edu/metchev/PHY688/Pollack_etal96_core_accretion.pdf

Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

Formation of the Giant Planets by Concurrant Accretion of Solids and Gas

Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.

https://science.sciencemag.org/content/sci/270/5233/53.full.pdf

Plio-Pleistocene African Climate

The Giotto space probe's ion mass spectrometer has obtained data on the composition and velocity distributions of cometary ions at distances of between 7.5 million and 1300 km from the comet Halley nucleus. Solar wind He(2+) was found throughout the coma, as close as 5000 km, with the He(+) produced by charge exchange being within about 200,000 km. A pile-up of heavy cometary ions was found at about 10,000 km from the nucleus. Inside the contact surface, which was found at about 4600 km, ion temperatures as low as about 340 K and outflow velocities of about 1 km/sec were found.

Ion composition and dynamics at comet Halley

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants, and the general population is exposed through products such as upholstery, building materials, insulation, electronic equipment, and contaminated food. PBDEs are added to polymers without being chemically bound and can leach into the environment, where they settle with air particles and sludge. They are persistent, and some—BDE-47, BDE-99, and BDE-153—can accumulate in lipid-rich tissues (Agency for Toxic Substances and Disease Registry 2004; Sjodin et al. 2003).

Concentrations of PBDE in human European breast milk samples are generally low compared with those in the United States, and considered to be well below the estimated lowest observed adverse effect level (LOAEL) of 1 mg/kg/day (Darnerud et al. 2001). Two technical mixtures, penta- and octa-mixtures of PBDEs, have been banned from use in Europe since 2003 (Darnerud et al. 2001), and Swedish studies indicated a decrease in breast milk levels since the middle of the 1990s (Meironyte et al.1999; Sjodin et al. 2003). However, annual production rates of some PBDEs are still considerable in some areas (Alaee et al. 2006; Betts 2002; Law et al. 2006). Animal studies show that some PBDEs exhibit endocrine-disrupting activity, which has been studied predominantly for thyroid hormone transport and metabolism (Legler and Brouwer 2003), but data on adverse effects on reproductive outcome after gestational exposure are also emerging (Lilienthal et al. 2006).

The prevalence of cryptorchidism in newborn boys appears to have increased in some areas, such as Great Britain and Denmark, over the past decades, and its current prevalence is considerably higher in Denmark than in Finland (Anonymous 1986; Boisen et al. 2004). Although the reason for this is as yet unknown, the rapid increase in prevalence suggests that environmental factors are involved (Sharpe 2006; Skakkebaek et al. 2001). Adverse effects of fetal exposure to environmental chemicals on testicular descent and hormonal function may be detectable during the short physiologic activation of the pituitary–gonadal axis at approximately 3 months of age (Andersson et al. 1998; Main et al. 2000, 2006b; Suomi et al. 2006).

In this study we aimed to evaluate the association between exposure to 14 PBDEs (BDEs 28, 47, 66, 71, 75, 77, 85, 99, 100,119, 138, 153, 154, 183) in newborn boys and the position and function of the testes.

Flame retardants in placenta and breast milk and cryptorchidism in newborn boys.

http://mnras.oxfordjournals.org/content/166/1/181.full.pdf

Hydrodynamics of the H2O Comet

From a study of cometary IUE spectra, a tentative identification of bands of the B-X systems of the SO molecule in the comet IRAS-Araki-Alcock in the 2200-2400 A region is reported, and it is suggested that sulphur compounds are more prevalent in comets than has been previously realized. S(+) and possibly SH are evident in comet Halley spectra, and new bands in the (A-X) system of CS and the (B-X) system of S2 are identified. The present results throw doubts on previous assessments of dust abundances from scattered continua in the 2900-3000 A region. The relatively strong abundance of S2 compared to OH in the Cernis and Bowell comets suggests that S2 is not well mixed and is not bound in H2O-ice.

Sulphur compounds in cometary IUE spectra

The abundances of diatomic molecules seen in the UV both give clues to the parent compounds and help unravel the gas and ion mass spectrometry. From IUE spectra of comet Halley, we find upper limits on SH and CS+ column densities, and estimates of probable NO, S2, and SO. In particular, judged from the 226 nm γ-band, NO was relatively abundant at 2–8 1013 cm−2 on March 9–14. The production rate of S2 was around 1 1027 molecules s −1 at that time, but both showed day-to-day variability by 2–3 times.

Some diatomic molecules from comet P/Halley’s UV spectra near spacecraft flybys

Orbiting spacecraft about Venus have revealed a partially penetrable boundary sheath with induced fields limiting solar wind effects on the atmosphere structure and evolution. Mars differs structurally, the explanation awaiting an orbiter mission such as the European Space Agency is considering. In weak comets gyro-radii exceed other scale lengths, while in active comets the gas and solar plasma couple over the largest scale, boundary sheaths being unimportant—as occurred during early rapid-outgassing phases of Venus and Mars.

Atmospheric interactions of planetary bodies with the solar wind

A particle moving through a sea of stochastic impulses gains energy from the sea; this is a long-established property of brownian motion, given theoretical backing in the fluctuation–dissipation theorem1. However, this energy gain is generally neglected in describing circumstellar dust grains as slowly spiralling into the central star under Poynting–Robertson (P–R) drag. Stochastic forces on circumsolar grains arise from low-frequency fluctuations in surface charge and interplanetary fields, as has long been recognized2,3, but previous studies have treated the mean orbital energy as constant4,5 or slowly decreasing6. I show here that stochastic heating can balance and indeed overwhelm the dissipative P–R drag for small grains (≲1 µm scale radius). Furthermore, the consequent drift to the outer Solar System may cancel the strong collisional source inferred7 for micrometre and sub-micrometre fragments, explaining how their present distribution is stable in time. More generally, the stochastic heating mechanism combined with collisional fragmentation sets limits on dust accretion onto cool stars.

Max K. Wallis

Papers

Hydrodynamics of the H2O Comet

Sulphur compounds in cometary IUE spectra

Some diatomic molecules from comet P/Halley’s UV spectra near spacecraft flybys

Atmospheric interactions of planetary bodies with the solar wind

Random fluctuations versus Poynting–Robertson drag on interplanetary dust grains