Authors:Yates et alAbstract:We use a simple organism lifecycle model to explore the viability of an atmospheric habitable zone (AHZ), with temperatures that could support Earth-centric life, which sits above an environment that does not support life. We illustrate this idea using the object WISE J085510.83-0714442.5, which is a cool, free-floating brown dwarf. We allow organisms to adapt to their atmospheric environment (described by temperature, convection, and gravity) by adopting different growth strategies that maximize their chance of survival and proliferation. We assume a constant upward vertical velocity through the AHZ. We found that the organism growth strategy is most sensitive to the magnitude of the atmospheric convection. Stronger convection supports the evolution of more massive organisms. For a purely radiative environment we find that evolved organisms have a mass that is an order of magnitude smaller than terrestrial microbes, thereby defining a dynamical constraint on the dimensions of life that an AHZ can support. Based on a previously defined statistical approach we infer that there are of order 109 Y brown dwarfs in the Milky Way, and likely a few tens of these objects are within ten parsecs from Earth. Our work also has implications for exploring life in the atmospheres of temperate gas giants. Consideration of the habitable volumes in planetary atmospheres significantly increases the volume of habitable space in the galaxy.
Friday, February 3, 2017
Do Y Class Brown Dwarfs Have Habitable Zones Within Their Atmospheres?
Thursday, February 2, 2017
T Tauri star V830 Tau has a hot Jupiter
Authors:Donati et alAbstract:We report results of an extended spectropolarimetric and photometric monitoring of the weak-line T Tauri star V830 Tau and its recently-detected newborn close-in giant planet. Our observations, carried out within the MaTYSSE programme, were spread over 91 d, and involved the ESPaDOnS and Narval spectropolarimeters linked to the 3.6-m Canada-France-Hawaii, the 2-m Bernard Lyot and the 8-m Gemini-North Telescopes. Using Zeeman-Doppler Imaging, we characterize the surface brightness distributions, magnetic topologies and surface differential rotation of V830 Tau at the time of our observations, and demonstrate that both distributions evolve with time beyond what is expected from differential rotation. We also report that near the end of our observations, V830 Tau triggered one major flare and two weaker precursors, showing up as enhanced red-shifted emission in multiple spectral activity proxies. With 3 different filtering techniques, we model the radial velocity (RV) activity jitter (of semi-amplitude 1.2 km s−1) that V830 Tau generates, successfully retrieve the 68 ± 11 m s−1 RV planet signal hiding behind the jitter, further confirm the existence of V830 Tau b and better characterize its orbital parameters. We find that the method based on Gaussian-process regression performs best thanks to its higher ability at modelling not only the activity jitter, but also its temporal evolution over the course of our observations, and succeeds at reproducing our RV data down to a rms precision of 35 m s−1. Our result provides new observational constraints on scenarios of star / planet formation and demonstrates the scientific potential of large-scale searches for close-in giant planets around T Tauri stars.
K2-60b & EPIC 216468514b: a hot Jupiter and hot Saturn
Authors:Eigmüller et alAbstract:We report the characterization and independant detection of K2-60b, as well as the detection and characterization of EPIC 216468514b, two transiting hot gaseous planets from the K2 space mission. We confirm the planetary nature of the two systems and determine their fundamental parameters combining the K2 time-series data with FIES@NOT and HARPS-N@TNG spectroscopic observations. K2-60b has a radius of 0.683 +/- 0.037 RJup and a mass of 0.426 +/- 0.037 MJup and orbits a G4V star with an orbital period of 3.00267 +/- 0.00006 days. EPIC 216468514b has a radius of 1.44 +/- 0.15RJup and a mass of 0.84 +/- 0.08 MJup and orbits an F9 IV star every 3.31392 +/- 0.00002 days. K2-60b is among the few planets at the edge of the so-called "desert" of short-period sub Jovian planets. EPIC 216468514b is a highly inflated Jovian planet orbiting an evolved star about to leave the main sequence.
Five New Hot Jupiters Discovered by HATSOUTH Survey
Authors:de Val-Borro et alAbstract:We report the discovery of five new transiting hot-Jupiter planets discovered by the HATSouth survey, HATS-31b through HATS-35b. These planets orbit moderately bright stars with V magnitudes within the range of $11.9$–$14.4$ mag while the planets span a range of masses of $0.88$–$1.22$ ${M}_{{\rm{J}}}$ and have somewhat inflated radii between $1.23$ and $1.64$ ${R}_{{\rm{J}}}$. These planets can be classified as typical hot Jupiters, with HATS-31b and HATS-35b being moderately inflated gas giant planets with radii of $1.64\pm 0.22$ ${R}_{{\rm{J}}}$ and ${1.464}_{-0.044}^{+0.069}$ ${R}_{{\rm{J}}}$, respectively, that can be used to constrain inflation mechanisms. All five systems present a higher Bayesian evidence for a fixed-circular-orbit model than for an eccentric orbit. The orbital periods range from $1.8209993\pm 0.0000016$ day for HATS-35b) to $3.377960\pm 0.000012$ day for HATS-31b. Additionally, HATS-35b orbits a relatively young F star with an age of $2.13\pm 0.51$ Gyr. We discuss the analysis to derive the properties of these systems and compare them in the context of the sample of well-characterized transiting hot Jupiters known to date.
Wednesday, February 1, 2017
Metal enrichment leads to low atmospheric C/O ratios in transiting giant exoplanets
Authors:Espinoza et alAbstract:We predict the carbon-to-oxygen (C/O) ratios in the hydrogen-helium envelope and atmospheres of a sample of nearly 50 relatively cool (Teq< 1000 K) transiting gas giant planets. The method involves planetary envelope metallicity estimates that use the structure models of Thorngren et al. (2016) and the disk and planetary accretion model of \"Oberg et al. (2011). We find that nearly all of these planets are strongly metal-enriched which, coupled with the fact that solid material is the main deliverer of metals in the protoplanetary disk, implies that the substellar C/O ratios of their accreted solid material dominate compared to the enhanced C/O ratio of their accreted gaseous component. We predict that these planets will have atmospheres that are typically reduced in their C/O compared to parent star values independent of the assessed formation locations, with C/O
The Migration Origin Story for Warm Jupiters Questioned
Authors:Antonini et alAbstract:Gas giants orbiting their host star within the ice line are thought to have migrated to their current locations from farther out. Here we consider the origin and dynamical evolution of observed Jupiters, focusing on hot and warm Jupiters with outer friends. We show that the majority of the observed Jupiter pairs (20 out of 24) are dynamically unstable if the inner planet is placed at gsim1 au distance from the stellar host. This finding is at odds with formation theories that invoke the migration of such planets from semimajor axes gsim1 au due to secular dynamical processes (e.g., secular chaos, Lidov–Kozai [LK] oscillations) coupled with tidal dissipation. In fact, the results of N-body integrations show that the evolution of dynamically unstable systems does not lead to tidal migration but rather to planet ejections and collisions with the host star. This and other arguments lead us to suggest that most of the observed planets with a companion could not have been transported from farther out through secular migration processes. More generally, by using a combination of numerical and analytic techniques, we show that the high-e LK migration scenario can only account for less than 10% of all gas giants observed between 0.1 and 1 au. Simulations of multiplanet systems support this result. Our study indicates that rather than starting on highly eccentric orbits with orbital periods above 1 yr, these "warm" Jupiters are more likely to have reached the region where they are observed today without having experienced significant tidal dissipation.
Why do Neptune Class Exoplanets Appear to be the Most Common?
Authors:Cubillos et alAbstract:We present a uniform analysis of the atmospheric escape rate of Neptune-like planets with estimated radius and mass (restricted to Mp<30m 167="" 25="" 27="" a="" and="" are="" at="" atmospheres="" atmospheric="" atom="" compare="" compute="" confirm="" consistent="" driven="" each="" energy-limited="" equilibrium="" escape="" estimate="" evaluated="" exhibit="" expected="" extreme="" extremely="" for="" further="" high-energy="" high="" hy="" hydrodynamic="" hydrogen-dominated="" hydrogen="" identify="" jeans="" lhy="" mass-loss="" mass="" maximum-possible="" models.="" of="" out="" parameter="" planet="" planetary="" planets="" radius="" rates.="" rates="" restricted="" sample="" simultaneously="" suggest="" tailored="" temperature.="" that="" the="" these="" to="" values="" we="" with="">0.1M⊕Gyr−1), well in excess of the energy-limited mass-loss rates. This constitutes a contradiction, since the hydrogen envelopes cannot be retained given the high mass-loss rates. We hypothesize that these planets are not truly under such high mass-loss rates. Instead, either hydrodynamic models overestimate the mass-loss rates, transit-timing-variation measurements underestimate the planetary masses, optical transit observations overestimate the planetary radii (due to high-altitude clouds), or Neptunes have consistently higher albedos than Jupiter planets. We conclude that at least one of these established estimations/techniques is consistently producing biased values for Neptune planets. Such an important fraction of exoplanets with misinterpreted parameters can significantly bias our view of populations studies, like the observed mass--radius distribution of exoplanets for example.
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