Day 1371

Monday.  Tuesday.  Wednesday.

1802.06794
Jupiter Analogues orbit stars with an average metallicity close to that of the Sun
Buchhave, et al

Jupiter played an important role in determining the structure and configuration of the Solar System.  Whereas hot-Jupiter type exoplanets preferentially form around metal-rich stars, the conditions required for the formation of planets with masses, orbits and eccentricities comparable to Jupiter (Jupiter analogues) are unknown.  Using spectroscopic metallicities, show that stars hosting Jupiter analogues have an average metallicity close to solar, in contrast to their hot-Jupiter and eccentric cool Jupiter counterparts, which orbit stars with super-solar metallicities.  Furthermore, the eccentricities of Jupiter analogues increase with host star metallicity, suggesting that planet-planet scatterings producing highly eccentric cool Jupiters could be more common in metal-rich environments.  To investigate a possible explanation for these metallicity trends, compare the observations to numerical simulations, which indicate that metal-rich stars typically form multiple Jupiters, leading to planet-planet interactions and, hence, a prevalence of either eccentric cool Jupiters or hot-Jupiters with circularized orbits.  Although the samples are small and exhibit variations in their metallicities, suggesting that numerous processes other than metallicity affect the formation of planetary systems, the data in hand suggests that Jupiter analogues and terrestrial-sized planets form around stars with average metallicities close to solar, whereas high metallicity systems preferentially host eccentric cool Jupitor or hot-Jupiters, indicating higher metallicity systems may not be favorable for the formation of planetary systems akin to the Solar System.


1802.07036
The habitability of our Evolving Galaxy
Gowanlock, Morrison

The notion of Galactic Habitable Zone (GHZ), or regions of the MW galaxy that preferentially maintain the conditions to sustain complex life, has recently gained attention due to the detection of numerous exoplanets and advances made in understanding habitability on the Earth and other environments.  Discuss what a habitable environment means on large spatial and temporal scales, which necessarily requires an approximated definition of habitability to make an assessment of the astrophysical conditions that may sustain complex life.  Discuss a few key exoplanet findings that directly relate to estimating the distribution of Earth-size planets in the Milky Way.  With a broad notion of habitability defined and major observable properties of the MW described, compare selected literature on the GHZ and postulate why the models yield differing predictions of the most habitable regions at the present day, which include: (1) the majority of the galactic disk; (2) an annular ring between 7-9 kpc, and (3) the galactic outskirts.  Briefly discuss the habitability of other galaxies as influenced by these studies.  Note that the dangers to biospheres in the Galaxy taken into account in these studies may be incomplete and discuss the possible role of Gamma-Ray Bursts and other dangers to life n the MW.  Speculate how changing astrophysical properties may affect the GHZ over time, including before the Earth formed, and describe how new observations and other related research may fit into the bigger picture of the habitability of the Galaxy.