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Sökning: WFRF:(Wahlund L O) > Wahlund Jan Erik

  • Resultat 1-7 av 7
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1.
  • Coustenis, A., et al. (författare)
  • TandEM : Titan and Enceladus mission
  • 2009
  • Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 23:3, s. 893-946
  • Tidskriftsartikel (refereegranskat)abstract
    • TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (MontgolfiSre) and possibly several landing probes to be delivered through the atmosphere.
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2.
  • Stephan, K., et al. (författare)
  • Regions of interest on Ganymede's and Callisto's surfaces as potential targets for ESA's JUICE mission
  • 2021
  • Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 208
  • Tidskriftsartikel (refereegranskat)abstract
    • The JUpiter Icy moons Explorer (JUICE) will investigate Ganymede's and Callisto's surfaces and subsurfaces from orbit to explore the geologic processes that have shaped and altered their surfaces by impact, tectonics, possible cryovolcanism, space weathering due to micrometeorites, radiation and charged particles as well as explore the structure and properties of the icy crust and liquid shell (Grasset et al., 2013). The best possible synergy of the JUICE instruments is required to answer the major science objective of this mission and to fully exploit the po-tential of the JUICE mission. Therefore, the JUICE team is aiming to define high priority targets on both Gany-mede's and Callisto's surfaces to support the coordination of the planning activities by the individual instrument teams. Based on the science objectives of the JUICE mission and the most recent knowledge of Ganymede's and Callisto's geologic evolution we propose a collection of Regions of Interest (RoIs), which characterize surface features and terrain types representing important traces of geologic processes, from past and/or present cryovolcanic and tectonic activity to space weathering processes, which are crucial to understand the geologic evolution of Ganymede and Callisto. The proposed evaluation of RoIs is based on their scientific importance as well as on the opportunities and conditions to observe them during the currently discussed mission profile.
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3.
  • Herique, A., et al. (författare)
  • Direct observations of asteroid interior and regolith structure : Science measurement requirements
  • 2018
  • Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 62:8, s. 2141-2162
  • Tidskriftsartikel (refereegranskat)abstract
    • Our knowledge of the internal structure of asteroids is, so far, indirect - relying entirely on inferences from remote sensing observations of the surface, and theoretical modeling of formation and evolution. What are the bulk properties of the regolith and deep interior? And what are the physical processes that shape asteroid internal structures? Is the composition and size distribution observed on the surface representative of the bulk? These questions are crucial to understand small bodies' history from accretion in the early Solar System to the present, and direct measurements are needed to answer these questions for the benefit of science as well as for planetary defense or exploration. Radar is one of the main instruments capable of sounding asteroids to characterize internal structure from sub-meter to global scale. In this paper, we review the science case for direct observation of the deep internal structure and regolith of a rocky asteroid of kilometer size or smaller. We establish the requirements and model dielectric properties of asteroids to outline a possible instrument suite, and highlight the capabilities of radar instrumentation to achieve these observations. We then review the expected science return including secondary objectives contributing to the determination of the gravitational field, the shape model, and the dynamical state. This work is largely inherited from MarcoPolo-R and AIDA/AIM studies.
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4.
  • Lammer, H., et al. (författare)
  • What makes a planet habitable?
  • 2009
  • Ingår i: The Astronomy and Astrophysics Review. - : Springer Science and Business Media LLC. - 0935-4956 .- 1432-0754. ; 17:2, s. 181-249
  • Forskningsöversikt (refereegranskat)abstract
    • This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological time scales and for planets which evolve to one-plate planets. The discoveries of methane-ethane surface lakes on Saturn's large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede, Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations of extraterrestrial life.
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5.
  • Lewis, G. R., et al. (författare)
  • The calibration of the Cassini-Huygens CAPS Electron Spectrometer
  • 2010
  • Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:3, s. 427-436
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the two-stage method used to calibrate the electron spectrometer (ELS), part of the plasma spectrometer (CAPS) on board the Cassini spacecraft currently in orbit around Saturn. The CAPS-ELS is a top-hat electrostatic analyser designed to measure electron fluxes between 0 5 eV and 26 keV The on-ground calibration method described here includes the production of photoelectrons, which are energised and passed into the CAPS-ELS in a purpose designed calibration facility. Knowledge of the intensity of these incident electrons and the subsequent instrument output provides an on-ground calibrated geometric factor. Comparative studies of physical quantities such as plasma density and electron differential flux calculated using on-ground calibration factor with the quantities deduced from the wave experiment and high energy electron detector provide in-flight calibration. The results of this are presented together with a comparison of the experimentally calibrated values with simulated calibration values.
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6.
  • Persoon, A. M., et al. (författare)
  • A diffusive equilibrium model for the plasma density in Saturn's magnetosphere
  • 2009
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:4, s. A04211-
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron density measurements have been obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument for more than 50 passes through Saturn's inner magnetosphere from 30 June 2004 to 30 September 2007. The electron densities are derived from RPWS measurements of the upper hybrid resonance frequency and span latitudes up to 35 degrees and L values from 3.6 to 10. The electron density measurements are combined with ion anisotropy measurements from the Cassini Plasma Spectrometer (CAPS) and electron temperature measurements from the RPWS and CAPS to develop a diffusive equilibrium model for the distribution of water group ions, hydrogen ions, and electrons in the inner region of Saturn's magnetosphere. The model uses an analytical solution of the field-aligned force equation, including the ambipolar electric field, to determine the equatorial ion densities and scale heights as a function of L. Density contour plots for water group ions, hydrogen ions, and electrons are presented.
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7.
  • Waite, J. H., Jr., et al. (författare)
  • Chemical interactions between Saturn's atmosphere and its rings
  • 2018
  • Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 362:6410
  • Tidskriftsartikel (refereegranskat)abstract
    • The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H-2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.
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  • Resultat 1-7 av 7

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