Carlson R.W.,Jet Propulsion Laboratory |
Baines K.H.,Jet Propulsion Laboratory |
Anderson M.S.,Jet Propulsion Laboratory |
Filacchione G.,Istituto di Astrofisica e Planetologia Spaziali |
Icarus | Year: 2016
The high altitude of Jupiter's Great Red Spot (GRS) may enhance the upward flux of gaseous ammonia (NH3) into the high troposphere, where NH3 molecules can be photodissociated and initiate a chain of chemical reactions with downwelling acetylene molecules (C2H2). These reactions, experimentally studied earlier by (Ferris and Ishikawa  Nature 326, 777-778) and (Ferris and Ishikawa  J. Amer. Chem. Soc. 110, 4306-4312), produce chromophores that absorb in the visible and ultraviolet regions. In this work we photolyzed mixtures of NH3 and C2H2 using ultraviolet radiation with a wavelength of 214nm and measured the spectral transmission of the deposited films in the visible region (400-740nm). From these transmission data we estimated the imaginary indices of refraction. Assuming that ammonia grains at the top of the GRS clouds are coated with this material, we performed layered sphere and radiative transfer calculations to predict GRS reflection spectra. Comparison of those results with observed and previously unreported Cassini visible spectra and with true-color images of the GRS show that the unknown GRS chromophore is spectrally consistent with the coupled NH3-C2H2 photochemical products produced in our laboratory experiments. Using high-resolution mass spectrometry and infrared spectroscopy we infer that the chromophore-containing residue is composed of aliphatic azine, azo, and diazo compounds. © 2016 Elsevier Inc.
Conway S.J.,CNRS Nantes Laboratory of Planetology and Geodynamics |
Hovius N.,University of Cambridge |
Barnie T.,University of Cambridge |
Besserer J.,CNRS Nantes Laboratory of Planetology and Geodynamics |
And 3 more authors.
Icarus | Year: 2012
This paper explores the origins and evolution of ice-rich interior mounds found within craters of the north polar region of Mars. We present a systematic study of impact craters above 65°N, and identify 18 craters that have interior mounds. At least 11 of these mounds are composed of water ice and geometric similarities suggest that dune-covered mounds may also have a water ice core. The mounds are found in the deeper craters in the north polar area and we suggest that these form a specific microclimate favorable for mound initiation and growth. It is likely that at least seven of the mounds have evolved as individual outliers, rather than conterminous with the main polar cap. Our observations suggest that the mounds are built up by atmospheric deposition, similar to that of the north polar layered deposits. Using a combination of remote sensing techniques enabling topographic, spectral, radar and image data analyses, we have documented the morphology, composition and stratigraphy of selected mounds. We advance and test four hypotheses for formation of these mounds: artesian outpouring from a deep aquifer, hydrothermal activation of ground ice, remnants of a more extensive polar cap, and atmospheric deposition on ice caps in meteorologically isolated locations. We propose that during periods when the perihelion was located in northern summer (most recently 10-25ka before present) the microclimate in these craters retarded the sublimation of CO 2 and water ice in northern spring, thus creating a cold trap for volatiles released as the seasonal cap retreated. This created a thick enough deposit of water ice to withstand sublimation over the summer and initiate a positive feedback leading to mound-building. Mounds without complete dune-cover may be in dynamic equilibrium with the ambient climate and show evidence of both present-day and past periods of erosion and aggradation. We conclude that the water ice mounds formed in deep impact craters in Mars' north polar region may contain sensitive records of past polar climate that may enhance our understanding of the CO 2-H 2O system in the polar regions. © 2012 Elsevier Inc..
De Michelis P.,Italian National Institute of Geophysics and Volcanology |
Consolini G.,Istituto di Astrofisica e Planetologia Spaziali |
Tozzi R.,Italian National Institute of Geophysics and Volcanology
Geophysical Research Letters | Year: 2015
The European Space Agency's Swarm mission provides a qualitatively new level of observational geomagnetic data, which allows us to study the spatial features of magnetic field fluctuations, capturing their essential characteristics and at the same time establishing a correlation with the dynamics of the systems responsible for the fluctuations. Our study aims to characterize changes in the scaling properties of the geomagnetic field's spatial fluctuations by evaluating the local Hurst exponent and to construct maps of this index at the Swarm's altitude (∼460km). Since a signal with a larger Hurst exponent is more regular and less erratic than a signal with a smaller one, the maps permit us to localize spatial structures characterized by different scaling properties. This study is an example of the potential of Swarm data to give new insights into ionosphere-magnetosphere coupling; at the same time, it develops new applications where changes in statistical parameters can be used as a local indicator of overall magnetospheric-ionospheric coupling conditions. Key Points Scaling features of magnetic spatiotemporal fluctuations at Swarm's altitude Change of the geomagnetic fluctuation scaling properties with activity level Ionospheric high-latitude turbulence ©2015. American Geophysical Union. All Rights Reserved.
Spinoglio L.,Istituto di Astrofisica e Planetologia Spaziali
Proceedings of the International Astronomical Union | Year: 2014
Various observational techniques have been used to survey galaxies and AGN, from X-rays to radio frequencies, both photometric and spectroscopic. I will review these techniques aimed at the study of galaxy evolution and of the role of AGNs and star formation as the two main energy production mechanisms. I will then present as a new observational approach the far-IR spectroscopic surveys that could be done with planned astronomical facilities of the next future, such as SPICA from the space and CCAT from the ground. Copyright © International Astronomical Union 2014.
Sadavoy S.I.,University of Victoria |
Sadavoy S.I.,National Research Council Canada |
Sadavoy S.I.,Max Planck Institute for Astronomy |
Di Francesco J.,University of Victoria |
And 24 more authors.
Astrophysical Journal Letters | Year: 2014
We use PACS and SPIRE continuum data at 160 μm, 250 μm, 350 μm, and 500 μm from the Herschel Gould Belt Survey to sample seven clumps in Perseus: B1, B1-E, B5, IC 348, L1448, L1455, and NGC 1333. Additionally, we identify and characterize the embedded Class 0 protostars using detections of compact Herschel sources at 70 μm as well as archival Spitzer catalogs and SCUBA 850 μm photometric data. We identify 28 candidate Class 0 protostars, four of which are newly discovered sources not identified with Spitzer. We find that the star formation efficiency of clumps, as traced by Class 0 protostars, correlates strongly with the flatness of their respective column density distributions at high values. This correlation suggests that the fraction of high column density material in a clump reflects only its youngest protostellar population rather than its entire source population. We propose that feedback from either the formation or evolution of protostars changes the local density structure of clumps. © 2014. The American Astronomical Society. All rights reserved.