Day 1130

Friday.

1608.00706
Was Venus the first habitable world of our Solar System?
Way, et al

Present-day Venus is an inhospitable place with surface temperatures approaching 750K and an atmosphere over 90 times as thick as present day Earth's.  Billions of years ago the picture may have been very different.  Create a suite of 3d climate simulations using topographic data from the Magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 billion years ago, present day Venus orbital parameters, an ocean volume consistent with current theory and measurements, and an atmospheric composition estimated for early Venus.  Using these parameters, find that such a world could have had moderate temperatures if Venus had a rotation period slower than about 16 Earth days, despite an incident solar flux 46-70% higher than modern Earth receives.  At its current rotation period of 243 days, Venus's climate could have remained habitable until at least 715 million years ago if it hosted a shallow primordial ocean.  These results demonstrate the vital role that rotation and topography play in understanding the climatic history of exoplanetary Venus-like worlds being discovered in the present epoch.


1608.01004
What can space resources do for astronomy and planetary science?
Elvis

The rapid cost growth of flagship space missions has created a crisis for astronomy and planetary science.  We have hit the funding wall.  For the past 3 decades scientists have not had to think much about how space technology would change within their planning horizon.  However, this time around enormous improvements in space infrastructure capabilities and, especially, costs are likely on the 20-year gestation periods for large space telescopes.  Commercial space will lower launch and spacecraft costs substantially, enable cost-effective on-orbit servicing, cheap lunar landers and interplanetary cubesats by the early 2020s.  A doubling of flagship launch rates is not implausible.  On a longer timescale it will enable large structures to be assembled and constructed in space.  These developments will change how we plan and design missions.


1608.01323
Angular momentum properties of haloes and their baryon content in the Illustris simulation
Zjupa, Springel

The angular momentum properties of virtualized DM haloes have bene measured with good statistics in collisionless N-body sims, but an equally accurate analysis of the baryonic spin is still missing.  Employ the Illustris simulation suite, one of the first simulations of galaxy formation with full hydrodynamics that produces a realistic galaxy population in a sizable volume, to quality the baryonic spin properties for more than ~320,000 haloes.  First compare the systematic differences between different spin parameter and halo definitions, and the impact of sample selection criteria on the derived properties.  Confirm that DM only haloes exhibit a close to self-similar spin distribution in mass and redshift of lognormal form.  However, the physics of galaxy formation radically changes the baryonic spin distribution.  While the DM component remans largely unaffected, strong trends with mass and redshift appear for the spin of diffuse gas and the formed stellar component.  With time, the baryons staying bound to the halo develop a misalignment of their spin vector with respect to DM, and increase their specific angular momentum by a factor of ~1.3 in the non-radiative case and ~1.8 in the full physics setup at z=0.  Show that this enhancement in baryonic spin can be explained by the combined effect of specific angular momentum transfer from DM onto gas during mergers and from feedback expelling low specific angular momentum gas from the halo.  The results challenge certain models for spin evolution and underlying the signifiant changes induced by baryonic physics in the structure of haloes.