| 1. |
- 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. |
- Galand, Marina, et al.
(författare)
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Ionization sources in Titan's deep ionosphere
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. A07312-
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Tidskriftsartikel (refereegranskat)abstract
- We analyze a multi-instrumental data set from four Titan encounters by the Cassini spacecraft to investigate in detail the formation of the ionosphere. The data set includes observations of thermospheric and ionospheric species and suprathermal electrons. A model describing the solar and electron energy deposition is used as an organizing element of the Cassini data set. We first compare the calculated secondary electron production rates with the rates inferred from suprathermal electron intensity measurements. We then calculate an effective electron dissociative recombination coefficient, applying three different approaches to the Cassini data set. Our findings are threefold: (1) The effective recombination coefficient derived under sunlit conditions in the deep ionosphere (< 1200 km) is found to be independent of solar zenith angle and flyby. Its value ranges from 6.9 x 10(-7) cm(3) s(-1) at 1200 km to 5.9 x 10(-6) cm(3) s(-1) at 970 km at 500 K. (2) The presence of an additional, minor source of ionization is revealed when the solar contribution is weak enough. The contribution by this non-solar source-energetic electrons most probably of magnetospheric origin-becomes apparent for secondary electron production rates, due to solar illumination alone, close to or smaller than about 3 x 10(-1) cm(-3) s(-1). Such a threshold is reached near the solar terminator below the main solar-driven electron production peak (< 1050 km). (3) Our ability to model the electron density in the deep ionosphere is very limited. Our findings highlight the need for more laboratory measurements of electron dissociative recombination coefficients for heavy ion species at high electron temperatures (especially near 500 K).
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| 3. |
- Ghail, Richard C., et al.
(författare)
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EnVision : taking the pulse of our twin planet
- 2012
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 337-363
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Tidskriftsartikel (refereegranskat)abstract
- EnVision is an ambitious but low-risk response to ESA's call for a medium-size mission opportunity for a launch in 2022. Venus is the planet most similar to Earth in mass, bulk properties and orbital distance, but has evolved to become extremely hostile to life. EnVision's 5-year mission objectives are to determine the nature of and rate of change caused by geological and atmospheric processes, to distinguish between competing theories about its evolution and to help predict the habitability of extrasolar planets. Three instrument suites will address specific surface, atmosphere and ionosphere science goals. The Surface Science Suite consists of a 2.2 m(2) radar antenna with Interferometer, Radiometer and Altimeter operating modes, supported by a complementary IR surface emissivity mapper and an advanced accelerometer for orbit control and gravity mapping. This suite will determine topographic changes caused by volcanic, tectonic and atmospheric processes at rates as low as 1 mm a (-aEuro parts per thousand 1). The Atmosphere Science Suite consists of a Doppler LIDAR for cloud top altitude, wind speed and mesospheric structure mapping, complemented by IR and UV spectrometers and a spectrophotopolarimeter, all designed to map the dynamic features and compositions of the clouds and middle atmosphere to identify the effects of volcanic and solar processes. The Ionosphere Science Suite uses a double Langmiur probe and vector magnetometer to understand the behaviour and long-term evolution of the ionosphere and induced magnetosphere. The suite also includes an interplanetary particle analyser to determine the delivery rate of water and other components to the atmosphere.
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| 4. |
- Lanchester, Betty, et al.
(författare)
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Separating and quantifying ionospheric responses to proton and electron precipitation over Svalbard
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A09322-
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Tidskriftsartikel (refereegranskat)abstract
- On 16 December 2001, a variable and structured aurora associated with a period of high solar wind velocity and low solar wind density was recorded through optical, radar, and particle measurements from the ground and space. A comprehensive analysis of this data set is carried out using a coupled auroral electron deposition and ion chemistry model. The observations include H beta, N(2)(+) 1N (0, 2), and O(+) (4)P-(4)D optical and electron density radar measurements from the ground, particle data from NOAA 16 and DMSP F14 satellites, and Doppler-shifted H Lyman alpha images from the IMAGE satellite. Modulations in the energy flux of both protons and electrons are seen in the NOAA 16 data as well as in the optical signatures measured on ground and from above. At the time of closest approach of NOAA 16, the observed emissions and electron density at the peak of an enhancement are well reproduced when precipitating protons and electrons with total fluxes of 0.23 and 3.0 mW m(-2), respectively, and mean energies of 2.50 and 0.25 keV, respectively, are used as input for the model. These values are consistent with those measured by the NOAA satellite. The resulting modeled emissions agree well with the ground measurements of enhanced emissions. The correlation between the emissions from N(2)(+) and O(+) suggests that they are primarily due to electron precipitation. This result is confirmed by the agreement between the measured and modeled emissions and by the values of extinction obtained for all three emissions. The modulations to the E region ionization can be explained by proton precipitation alone, while soft electrons are responsible for the changes to the ionization at higher altitudes.
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| 5. |
- Lavvas, Panayotis, et al.
(författare)
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Aerosol growth in Titan's ionosphere
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:8, s. 2729-2734
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Tidskriftsartikel (refereegranskat)abstract
- Photochemically produced aerosols are common among the atmospheres of our solar system and beyond. Observations and models have shown that photochemical aerosols have direct consequences on atmospheric properties as well as important astrobiological ramifications, but the mechanisms involved in their formation remain unclear. Here we show that the formation of aerosols in Titan's upper atmosphere is directly related to ion processes, and we provide a complete interpretation of observed mass spectra by the Cassini instruments from small to large masses. Because all planetary atmospheres possess ionospheres, we anticipate that the mechanisms identified here will be efficient in other environments as well, modulated by the chemical complexity of each atmosphere.
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| 6. |
- Tinetti, Giovanna, et al.
(författare)
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The science of EChO
- 2010
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 6:S276, s. 359-370
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Tidskriftsartikel (refereegranskat)abstract
- The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life. The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole. EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates. © International Astronomical Union 2011.
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