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Trending Papers in earth and planetary astrophysics

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The presence of phosphine gas suggests the potential for life within the clouds of Venus
From Paper: Phosphine gas in the cloud decks of Venus
Authors:
Greaves, Jane S., et al
Published: Sep 2020
  • The presence of PH3 could be due to unknown photochemistry or geochemistry, or possibly life
  • PH3 meets most criteria for a biosignature-gas search, but is challenging as many of its spectral features are strongly absorbed by Earth’s atmosphere.
Submitted by Age Old
2
The Search for Planet and Planetesimal Transits of White Dwarfs with the Zwicky Transient Facility
Author:
Keaton J. Bell
Published: Nov 2019
Planetary materials orbiting white dwarf stars reveal the ultimate fate of the planets of the Solar System and all known transiting exoplanets. Observed metal pollution and infrared excesses from debris disks support that planetary systems or their remnants are common around white dwarf stars; however, these planets are difficult to detect since a very high orbital inclination angle is required for a small white dwarf to be transited, and these transits have very short (minute) durations. The low odds of catching individual transits could be overcome by a sufficiently wide and fast photometric survey. I demonstrate that, by obtaining over 100 million images of white dwarf stars with 30-second exposures in its first three years, the Zwicky Transient Facility (ZTF) is likely to record the first exoplanetary transits of white dwarfs, as well as new systems of transiting, disintegrating planetesimals. In these proceedings, I describe my project strategy to discover these systems using the ZTF data.
Retrieved from arxiv
2
Does the Neptunian system of satellites challenge a gravitational origin for the Pioneer anomaly?
Author:
Lorenzo Iorio
Published: Dec 2009
If the Pioneer Anomaly (PA) was a genuine dynamical effect of gravitationalorigin, it should also affect the orbital motions of the solar system's bodiesmoving in the space regions in which the PA manifested itself in its presentlyknown form, i.e. as a constant and uniform acceleration approximately directedtowards the Sun with a non-zero magnitude APio = (8.74 +/- 1.33) x 10^-10 ms^-2 after 20 au from the Sun. In this paper we preliminarily investigate itseffects on the orbital motions of the Neptunian satellites Triton, Nereid andProteus, located at about 30 au from the Sun, both analytically andnumerically. Extensive observational records covering sev- eral orbitalrevolutions have recently been analyzed for them, notably improving theknowledge of their orbits. Both analytical and numerical calculations, limitedto the direct, Neptune-satellite interaction, show that the peak-to-peakamplitudes of the PA-induced radial, transverse and out-of-plane perturbationsover one century are up to 300 km, 600 km, 8 m for Triton, 17,500 km, 35,000km, 800 km for Nereid, and 60 km, 120 km, 30 m for Proteus. The correspondingorbital uncertainties ob- tained from a recent analysis of all the dataavailable for the satellites considered are, in general, smaller by one-twoorders of magnitude, although obtained without modeling a Pioneer-likeextra-force. Further investigations based on a re-processing of the satellites'real or simulated data with modified equations of motions including anadditional Pioneer-type force as well are worth being implemented and may shedfurther light on this important issue.
Retrieved from arxiv
2
Analyzing the designs of planet finding missions
Authors:
D. Savransky, N. J. Kasdin, E. Cady
Published: Mar 2009
We present a framework for the analysis of direct detection planet findingmissions using space telescopes. This framework generates simulations ofcomplete missions, with varying populations of planets, to produce ensembles ofmission simulations, which are used to calculate distributions of missionscience yields. We describe the components of a mission simulation, includingthe complete description of an arbitrary planetary system, the description of aplanet finding instrument, and the modeling of a target system observation.These components are coupled with a decision modeling algorithm, which allowsus to automatically generate mission timelines with simple mission rules thatlead to an optimized science yield. Along with the details of ourimplementation of this algorithm, we discuss validation techniques and possiblefuture refinements. We apply this analysis technique to four mission conceptswhose common element is a 4m diameter telescope aperture: an internal pupilmapping coronagraph with two different inner working angles, an externalocculter, and the THEIA XPC multiple distance occulter. The focus of this studyis to determine the ability of each of these designs to achieve one of theirmost difficult mission goals - the detection and characterization of Earth-likeplanets in the habitable zone. We find that all four designs are capable ofdetecting on the order of 5 Earth-like planets within a 5 year mission, even ifwe assume that only 1 out of every 10 stars has such a planet. The designs dodiffer significantly in their ability to characterize the planets they find.Along with science yield, we also analyze fuel usage for the two occulterdesigns, and discuss the strengths and weaknesses of each of the missionconcepts.
Retrieved from arxiv
2
Oscillatory migrating magnetic fields in helical turbulence in spherical domains
Authors:
Dhrubaditya Mitra, Reza Tavakol, Petri J. Käpylä, Axel Brandenburg
Published: Jan 2009
We present direct numerical simulations of the equations of compressiblemagnetohydrodynamics in a wedge-shaped spherical shell, without shear, but withrandom helical forcing which has negative (positive) helicity in the northern(southern) hemisphere. We find a large-scale magnetic field that is nearlyuniform in the azimuthal direction and approximately antisymmetric about theequator. Furthermore, the large-scale field in each hemisphere oscillates onnearly dynamical time scales with reversals of polarity and equatorwardmigration. Corresponding mean-field models also show similar migratoryoscillations with a frequency that is nearly independent of the magneticReynolds number. This mechanism may be relevant for understanding equatorwardmigration seen in the solar dynamo.
Retrieved from arxiv
1
Accretion in Protoplanetary Disks by Collisional Fusion
Author:
J. S. Wettlaufer
Published: Nov 2009
The formation of a solar system is believed to have followed a multi-stageprocess around a protostar. Whipple first noted that planetesimal growth byparticle agglomeration is strongly influenced by gas drag; there is a"bottleneck" at the meter scale with such bodies rapidly spiraling into thecentral star, whereas much smaller or larger particles do not. Thus, successfulplanetary accretion requires rapid planetesimal growth to km scale. A commonlyaccepted picture is that for collisional velocities $V_c$ above a certainthreshold collisional velocity, ${V_{th}} \sim$ 0.1-10 cm s$^{-1}$, particleagglomeration is not possible; elastic rebound overcomes attractive surface andintermolecular forces. However, if perfect sticking is assumed for allcollisions the bottleneck can be overcome by rapid planetesimal growth. Whileprevious work has dealt explicitly with the influences of collisional pressuresand the possibility of particle fracture or penetration, the basic role of thephase behavior of matter--phase diagrams, amorphs and polymorphs--has beenneglected. Here it is demonstrated that novel aspects of surface phasetransitions provide a physical basis for efficient sticking through collisionalmelting or amphorph-/polymorphization and fusion to extend the collisionalvelocity range of primary accretion to $\Delta V_c \sim$ 1-100 m s$^{-1}$,which bound both turbulent RMS speeds and the velocity differences betweenboulder sized and small grains $\sim$ 1-50 m s$^{-1}$. Thus, as inspiralingmeter sized bodies collide with smaller particles in this high velocitycollisional fusion regime they grow rapidly to km scales and hence settle intostable Keplerian orbits in $\sim$ 10$^5$ years before photoevaporative windclears the disk of source material.
Retrieved from arxiv
0
Jupiter's North Equatorial Belt and Jet: III, The 'great northern upheaval' in 2012
Authors:
John H. Rogers, Gianluigi Adamoli
Published: Sep 2018
In Paper II we described the extreme changes in Jupiter's North EquatorialBelt (NEB) which took place in 2011-12: quiescence, narrowing, and fading ofthe belt, along with acceleration of the prograde NEBs jet to super-fast speed.Here we describe how this anomalous state was terminated in 2012, in a rapidand vigorous disturbance known as a NEB Revival, the first in living memory. Atthe same time, the North Temperate Belt (NTB) had entered a similar preparatorystate, which was terminated by a NTB Revival initiated by a typical outbreak onthe super-fast NTBs jet. The two concurrent Revivals appeared to constitute a'great northern upheaval' that extended from the equator to 38N, which may havebeen the first such event ever recorded. We compare this dual event with themore typical 'Global Upheavals', which consist of near-simultaneous Revivals ofthe NTB and the South Equatorial Belt (SEB), along with equatorial coloration,and we discuss the current understanding of Global Upheavals.
Retrieved from arxiv
0
MOPSS II: Extreme Optical Scattering Slope for the Inflated Super-Neptune HATS-8b
Authors:
E. M. May, T. Gardner, E. Rauscher, J. D. Monnier
Published: Sep 2018
We present results for the inflated super-Neptune HATS-8b from MOPSS, TheMichigan Optical Planetary Spectra Survey. This program is aimed at creating adatabase of optical planetary transmission spectra all observed, reduced, andanalyzed with a uniform method for the benefit of enabling comparativeexoplanet studies. HATS-8b orbits a G dwarf and is a low density super-Neptune,with a radius of 0.873 R$_{Jup}$, a mass of 0.138 M$_{Jup}$, and a density of0.259 g/cm$^3$. Two transits of HATS-8b were observed in July and August of2017 with the IMACS instrument on the Magellan Baade 6.5m telescope. We find anenhanced scattering slope that differs between our two nights. These slopes arestronger than one due only to Rayleigh scattering and cannot be fully explainedby unocculted star spots. We explore the impact of condensates on thescattering slope and determine that MnS particulates smaller than 10$^{-2}\mu$mcan explain up to 80\% of our measured slope if the planet is warmer thanequilibrium, or 50\% of the slope at the equilibrium temperature of the planetfor a low mean molecular weight atmosphere. The scattering slope that weobserve is thus beyond even the most extreme case predicted by theory. Wesuggest further follow up on this target and host star to determine if thetemporal variation of the slope is primarily due to stellar or planetaryeffects, and to better understand what these effects may be.
Retrieved from arxiv
0
Meteoritic Abundances of Fatty Acids and Potential Reaction Pathways in Planetesimals
Authors:
James C. -Y. Lai, Ben K. D. Pearce, Ralph E. Pudritz, Drake Lee
Published: Sep 2018
The origin of fatty acids on the prebiotic Earth is important as they likelyformed the encapsulating membranes of the first protocells. Carbon-richmeteorites (i.e., carbonaceous chondrites) such as Murchison and Tagish Lakeare well known to contain these molecules, and their delivery to the earlyplanet by intense early meteorite bombardments constitutes a key prebioticsource. We collect the fatty acid abundances measured in various carbonaceouschondrites from the literature and analyze them for patterns and correlations.Fatty acids in meteorites include straight-chain and branched-chainmonocarboxylic and dicarboxylic acids up to 12 carbons in length---fatty acidswith at least 8 carbons are required to form vesicles, and modern cellmembranes employ lipids with ~12--20 carbons. To understand the origin ofmeteoritic fatty acids, we search the literature for abiotic fatty acidreaction pathways and create a candidate list of 11 reactions that couldpotentially produce these fatty acids in meteorite parent bodies.Straight-chain monocarboxylic acids (SCMA) are the dominant fatty acids inmeteorites, followed by branched-chain monocarboxylic acids (BCMA). SCMA aremost abundant in CM2 and Tagish Lake (ungrouped) meteorites, ranging on averagefrom 10$^2$ ppb to 4x10$^5$ ppb, and 10$^4$ ppb to 5x10$^6$ ppb, respectively.In CM, CV, and Tagish Lake meteorites, SCMA abundances generally decrease withincreasing carbon chain length. Conversely, SCMA abundances in CR meteoritespeak at 5 and 6 carbons in length, and decrease on either side of this peak.This unique CR fatty acid distribution may hint at terrestrial contamination,or that certain fatty acid reactions mechanisms are active in differentmeteorite parent bodies (planetesimals). We identify Fischer-Tropsch-typesynthesis as the most promising pathway for further analysis in the productionof fatty acids in planetesimals.
Retrieved from arxiv
0
Polarimetry of Water Ice Particles Providing Insights on Grain Size and Degree of Sintering on Icy Planetary Surfaces
Authors:
Olivier Poch, Romain Cerubini, Antoine Pommerol, Bernhard Jost, Nicolas Thomas
Published: Sep 2018
The polarimetry of the light scattered by planetary surfaces is a powerfultool to provide constraints on their microstructure. To improve theinterpretation of polarimetric data from icy surfaces, we have developed thePOLarimeter for ICE Samples (POLICES) complementing the measurement facilitiesof the Ice Laboratory at the University of Bern. The new setup uses a highprecision Stokes polarimeter to measure the degree of polarization in thevisible light scattered by surfaces at moderate phase angles (from 1.5 to30{\deg}). We present the photometric and polarimetric phase curves measured onvarious surfaces made of pure water ice particles having well-controlled sizeand shape (spherical, crushed, frost). The results show how the amplitude andthe shape of the negative polarization branch change with the particles sizesand the degree of metamorphism of the ice. We found that fresh frost formed bywater condensation on cold surfaces has a phase curve characterized byresonances (Mie oscillations) indicating that frost embryos are transparentmicrometer-sized particles with a narrow size distribution and spherical shape.Comparisons of these measurements with polarimetric observations of the icysatellites of the Solar System suggest that Europa is possibly covered byrelatively coarser (~40-400 {\mu}m) and more sintered grains than Enceladus andRhea, more likely covered by frost-like particles of few micrometers inaverage. The great sensitivity of polarization to grain size and degree ofsintering makes it an ideal tool to detect hints of ongoing processes on icyplanetary surfaces, such as cryovolcanism.
Retrieved from arxiv
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