Yudhijit Bhattacharjee

Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500 light-years away. Because such stars make up three-quarters of all stars in the Milky Way, the finding could open a wide new hunting ground for extraterrestrial life.

Reference
Bhattacharjee Y (2014) Almost-Earth Tantalizes Astronomers With Promise of Worlds to Come. Science 344:249.
[doi:10.1126/science.344.6181.249]
Reprinted with permission from AAAS

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Elisa V. Quintana¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043, USA.
²NASA Ames Research Center, Moffett Field, CA 94035, USA.

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star’s radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

Reference
Quintana et al. (2014) An Earth-Sized Planet in the Habitable Zone of a Cool Star. Science 344:277.
[doi:10.1126/science.1249403]
Reprinted with permission from AAAS

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Indhu Varatharajan, Neeraj Srivastava and Sripada V.S. Murty

PLANEX, Physical Research Laboratory, Ahmedabad 380009, India

A comparative assessment of the mineralogy of young basalts (~1.2 Ga to ~2.8 Ga) from the western nearside, Moscoviense basin, and the Orientale basin of the Moon has been made using Level 2 Moon Mineralogy Mapper (M³) data from the Chandrayaan-1 mission. Spectral data characteristics of the individual units have been generated from fresh small craters to minimize the complications due to space weathering. Representative spectra for individual units and the derived spectral parameters (Band centers and Integrated Band Depth Ratio) have been used to study composition of these young basalts. A modified approach of Gaffey et al. (2002) (for olivine-pyroxene mixtures) and the methodology of Adams (1974) (for interpreting pyroxene type) have been used to improve our understanding of the spectral behavior of these basalts. Most of the young basalts of Oceanus Procellarum are characterized by abundant olivines and they show complex volcanic history. Vast exposures of olivine concentrated units having higher abundance of olivine content than high-Ca pyroxenes are emplaced in the northern Oceanus Procellarum region. Mostly, they show distinct stratigraphic gradation with the immediately underlying units of relatively lower olivine content. The Moscoviense unit shows signatures of Fe-rich glasses along with clinopyroxenes. The basalts of Orientale basin are typically devoid of olivine and are rich in high-Ca pyroxene. Thus, mineralogy of these mare basalts which erupted during the late stage volcanism vary across the Moon’s surface; however, broader observations reveal apparently higher FeO content in the younger basalts of western nearside and Orientale region.

Reference
Varatharajan I, Srivastava N and Murty SVS (in press) Mineralogy of young lunar mare basalts: Assessment of temporal and spatial heterogeneity using M3 data from Chandrayaan-1. Icarus
[doi:10.1016/j.icarus.2014.03.045]
Copyright Elsevier

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Kévin Baillié and Sébastien Charnoz

Laboratoire AIM-LADP, Université Paris Diderot/CEA/CNRS, F-91191 Gif sur Yvette, France

Observations of protoplanetary disks show that some characteristics seem recurrent, even in star formation regions that are physically distant such as surface mass density profiles varying as r⁻¹ or aspect ratios of about 0.03–0.23. Accretion rates are also recurrently found around 10⁻⁸–10⁻⁶ M_☉ yr⁻¹ for disks that have already evolved. Several models have been developed in order to recover these properties. However, most of them usually simplify the disk geometry if not its mid-plane temperature. This has major consequences for modeling the disk evolution over millions of years and consequently planet migration. In the present paper, we develop a viscous evolution hydrodynamical numerical code that simultaneously determines the disk photosphere geometry and the mid-plane temperature. We then compare our results of long-term simulations with similar simulations of disks with a constrained geometry along the Chiang & Goldreich prescription (d lnH/d lnr = 9/7). We find that the constrained geometry models provide a good approximation of the disk surface density evolution. However, they differ significantly regarding the temperature–time evolution. In addition, we find that shadowed regions naturally appear at the transition between viscously dominated and radiation-dominated regions that falls in the region of planetary formation. We show that χ (photosphere height to pressure scale height ratio) cannot be considered a constant, which is consistent with the findings of Watanabe & Lin. Comparisons with observations show that all disks naturally evolve toward a shallow surface density disk (Σ∝r⁻¹). The mass flux across the disk typically stabilizes in about 1 Myr.

Reference
Baillié K and Charnoz C (2014) Time Evolution of a Viscous Protoplanetary Disk with a Free Geometry: Toward a More Self-consistent Picture. The Astrophysical Journal 786:35.
[doi:10.1088/0004-637X/786/1/35]

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