Day 1135

Monday.

1608.03743
The insight into the dark side.  I.  The pitfalls of the dark halo parameters estimation
Saburova, Kasparov, Katkov

[...] Pseudoisotehermal, Burkert and NFW dark halo parameters for mass modeling of the rotation curves.  Use two variants of models in which the M/L ratios of disk and bulge were (1) taken as free parameters, (2) fixed in a narrow range according to the models of stellar populations.  Show that, due to the degeneracy between the central densities and the radial scales of the dark haloes, there are considerable uncertainties of their concentration estimates.  It is also impossible to draw any firm conclusion about universality of the dark halo column density based on mass-modeling of even with a high quality rotation curve.  The problem is not solved by fixing the density of baryonic matter.  In contrast, the estimates of dark halo mass within optical radius are much more reliable.  Demonstrate that one can evaluate successfully the halo mass using the pure best-fitting method without any restrictions on the M/L ratio.


1608.03891
Could Cirrus clouds have warmed early Mars?
Ramirez, Kasting

The presence of the ancient valley networks on Mars indicates that the climate at 3.8 Ga was warm enough to allow substantial liquid water to flow on the martian surface for extended periods of time.  However, the mechanism for producing this warming continues to be debated.  One hypothesis is that Mars could have been kept warm by global cirrus cloud decks in a CO2-H2O atmosphere containing at least 0.25 bar of CO2 (Urata+Toon, 2013).  Initial warming from some other process, e.g., impacts, would be required to make this model work.  Those result were generated using the CAM 3D global climate model.  The calculations indicate that cirrus cloud decks could have produced global mean surface temerpatures above freezing, but only if cirrus cloud cover approaches ~70-100% and if other cloud properties (e.g., height, optical depth, particle size) are chosen favorably.  However, at more realistic cirrus cloud fractions, or if cloud parameters are not optimal, cirrus clouds do not provide the necessary warming, suggesting that other greenhouse mechanisms are needed.