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- Arridge, Christopher S., et al.
(författare)
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Uranus Pathfinder : exploring the origins and evolution of Ice Giant planets
- 2012
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 753-791
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Tidskriftsartikel (refereegranskat)abstract
- The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015-2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz-Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036-2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments.
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| 2. |
- Xystouris, Georgios, et al.
(författare)
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Estimating the optical depth of Saturn's main rings using the Cassini Langmuir Probe
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 526:4, s. 5839-5860
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Tidskriftsartikel (refereegranskat)abstract
- A Langmuir Probe (LP) measures currents from incident charged particles as a function of the applied bias voltage. While onboard a spacecraft the particles are either originated from the surrounding plasma, or emitted (e.g. through photoemission) from the spacecraft itself. The obtained current-voltage curve reflects the properties of the plasma in which the probe is immersed into, but also any photoemission due to illumination of the probe surface: As photoemission releases photoelectrons into space surrounding the probe, these can be recollected and measured as an additional plasma population. This complicates the estimation of the properties of the ambient plasma around the spacecraft. The photoemission current is sensitive to the extreme ultraviolet (UV) part of the spectrum, and it varies with the illumination from the Sun and the properties of the LP surface material, and any variation in the photoelectrons irradiance can be measured as a change in the current voltage curve. Cassini was eclipsed multiple times by Saturn and the main rings over its 14 yr mission. During each eclipse the LP recorded dramatic changes in the current-voltage curve, which were especially variable when Cassini was in shadow behind the main rings. We interpret these variations as the effect of spatial variations in the optical depth of the rings and hence use the observations to estimate the optical depth of Saturn's main rings. Our estimates are comparable with UV optical depth measurements from Cassini's remote sensing instruments.
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