International Space Science Institute
International Space Science Institute
Linsky J.L.,University of Colorado and NIST |
Linsky J.L.,International Space Science Institute
Annual Review of Astronomy and Astrophysics | Year: 2017
The discovery of exoplanets and the desire to understand their atmospheric chemical composition and habitability provides a new rationale for understanding the radiation from X-rays to radio wavelengths emitted by their host stars. Semiempirical models of stellar atmospheres that include accurate treatment of radiative transfer of all important atoms, ions, and molecules provide the essential basis for understanding a star's emitted radiation that is our main data source for characterizing a star and the radiation environment of its exoplanets. In Solar-type and cooler stars, the ultraviolet and extreme ultraviolet radiation formed in their chromospheres and transition regions drive the photochemistry in exoplanet atmospheres. In this review, I describe and critique the development of semiempirical static and time-dependent models of the chromospheres and transition regions of the Sun and cooler stars as well as the spectroscopic diagnostics upon which these models are based. The related topics of stellar coronae and winds and their theoretical bases are beyond the scope of this review. © Copyright 2017 by Annual Reviews. All rights reserved.
Zacharias P.,International Space Science Institute |
Zacharias P.,University of Oslo
Surveys in Geophysics | Year: 2014
With the advent of space-based total solar irradiance (TSI) observations about 35 years ago, researchers' understanding of solar variability and its causes has greatly improved. Controversies regarding the cross-calibration of the data from various TSI instruments have resulted in many different TSI composite time series. These composites agree well with each other on timescales ranging from days to years, but due to the limited stability of the instruments contributing to the composites, their quality is not yet sufficient to unambiguously detect possible changes between subsequent cycle minima. In this paper, the construction of the three most prominent TSI composite time series and the underlying TSI models is addressed. The difficulties associated with the cross-calibration of the data are considered, and the viewpoints of the different groups involved in the development of the composites are discussed. © 2014 Springer Science+Business Media Dordrecht.
Agency: European Commission | Branch: FP7 | Program: CP-CSA-Infra | Phase: INFRA-2008-1.1.1 | Award Amount: 7.39M | Year: 2009
The Europlanet RI project will provide the European planetary science community with a unique research infrastructure, combining access to a suite of state of the art facilities while fostering their joint development and integration in terms of capacity and performance. This research infrastructure will include access to laboratory and field site facilities, advanced modelling, simulation and data analysis resources and to data produced by space missions and ground-based telescopes hence maximising the scientific impact of major European space missions and ground-based installations. Access will be provided in two forms. Three coordinated Trans National Access activities will open to many users the unique range of laboratory and field site facilities selected for this project. In parallel, the IDIS e-service will provide a user-friendly web-based access to the available planetary science data, information and software tools. Four Joint Research Activities will broaden the scope of the infrastructure, opening access to new field sites, offering new models and data analysis tools for users and widening the opportunity of remote data access by progressively upgrading IDIS into a Planetary Virtual Observatory. Four complementary networking activities will publicize the objectives and opportunities of Europlanet RI and disseminate project results amongst the scientific community, industries, SMEs, space agencies and the public. They will consolidate the establishment of a European Research Area for planetary science and exploration. Building on the synergies between its services, joint research activities and networking activities, Europlanet RI will provide the ideal scientific and technical environment to fully analyse data from past and present planetary missions and prepare the next generation of missions. In this way it will play a vital role in establishing the European Community as a leading player in planetary and space exploration.
Koumoutsaris S.,International Space Science Institute |
Bey I.,ETH Zurich
Atmospheric Chemistry and Physics | Year: 2012
Quantifying trends in surface ozone concentrations is critical for assessing pollution control strategies. Here we use observations and results from a global chemical transport model to examine the trends (1991-2005) in daily maximum 8-h average concentrations in summertime surface ozone at rural sites in Europe and the United States (US). We find a decrease in observed ozone concentrations at the high end of the probability distribution at many of the sites in both regions. The model attributes these trends to a decrease in local anthropogenic ozone precursors, although simulated decreasing trends are overestimated in comparison with observed ones. The low end of observed distribution show small upward trends over Europe and the western US and downward trends in Eastern US. The model cannot reproduce these observed trends, especially over Europe and the western US. In particular, simulated changes between the low and high end of the distributions in these two regions are not significant. Sensitivity simulations indicate that emissions from far away source regions do not affect significantly summer ozone trends at both ends of the distribution in both Europe and US. Possible reasons for discrepancies between observed and simulated trends are discussed. © 2012 Author(s). CC Attribution 3.0 License.
Bengtsson L.,University of Reading |
Bengtsson L.,International Space Science Institute
Tellus, Series B: Chemical and Physical Meteorology | Year: 2013
The climate of the Earth, like planetary climates in general, is broadly controlled by solar irradiation, planetary albedo and emissivity as well as its rotation rate and distribution of land (with its orography) and oceans. However, the majority of climate fluctuations that affect mankind are internal modes of the general circulation of the atmosphere and the oceans. Some of these modes, such as El Niño-Southern Oscillation (ENSO), are quasi-regular and have some longer-term predictive skill; others like the Arctic and Antarctic Oscillation are chaotic and generally unpredictable beyond a few weeks. Studies using general circulation models indicate that internal processes dominate the regional climate and that some like ENSO events have even distinct global signatures. This is one of the reasons why it is so difficult toseparate internal climate processes from external ones caused, for example, by changes in greenhouse gases and solar irradiation. However, the accumulation of the warmest seasons during the latest two decades is lending strong support to the forcing of the greenhouse gases. As models are getting more comprehensive, they show a gradually broader range of internal processes including those on longer time scales, challenging the interpretation of the causes of past and present climate events further. © 2013 L. Bengtsson.
Von Steiger R.,International Space Science Institute |
Von Steiger R.,University of Bern |
Zurbuchen T.H.,University of Michigan
Journal of Geophysical Research: Space Physics | Year: 2011
During its nearly 19-year mission, Ulysses pioneered novel measurements of the three-dimensional heliosphere and particularly in situ observations of high-latitude solar wind from polar coronal holes (PCHs). Winds from PCHs exhibit constant elemental abundances to within the limits of the measurements, indicative of the fact that such winds truly provide a ground state of solar wind composition. However, these solar wind streams show long-term variability in the composition of ionic charge states frozen into the low corona. The C and O freeze-in temperatures measured in high-latitude solar wind have decreased ∼10% as compared to the previous solar minimum and are now around 0.87 and 1.01 MK, respectively. The ionization states of Si and Fe also exhibit a substantial cooling with a reduction of 0.4 and 0.5 charge states, respectively. We show that these observations are indicative of an overall decrease of coronal temperature, forming a trend toward cooler PCH temperature persisting for over 14 years. We support these observations with a detailed and comprehensive description of the data analysis processes relevant for Ulysses SWICS and similar instruments. Copyright 2011 by the American Geophysical Union.
Perri S.,International Space Science Institute |
Carbone V.,University of Calabria |
Veltri P.,University of Calabria
Astrophysical Journal Letters | Year: 2010
Power spectra of the magnetic field in solar wind display a Kolmogorov law f-5/3 at intermediate range of frequencies f, say within the inertial range. Two spectral breaks are also observed: one separating the inertial range from an f-1 spectrum at lower frequencies, and another one between the inertial range and an f-7/3 spectrum at higher frequencies. The breaking of fluid-like turbulence at high frequencies has been attributed to either the occurrence of kinetic Alfvén wave fluctuations above the ion-cyclotron frequency or to whistler turbulence above the frequency corresponding to the proton gyroradius. Using solar wind data, we show that the observed highfrequency spectral break seems to be independent of the distance from the Sun, and then of both the ion-cyclotron frequency and the proton gyroradius. We suppose that the observed high-frequency break could be either caused by a combination of different physical processes or associated with a remnant signature of coronal turbulence. © 2010. The American Astronomical Society. All rights reserved.
Balogh A.,International Space Science Institute |
Balogh A.,Imperial College London
Space Science Reviews | Year: 2010
The nature and diversity of the magnetic properties of the planets have been investigated by a large number of space missions over the past 50 years. It is clear that without the magnetic field measurements that have been carried out in the vicinity of all the planets, the state of their interior and their evolution since their formation would not be understood even though questions remain about how the different planetary dynamos (in six of the eight planets) work. This paper describes the motivation for making magnetic field measurements, the instrumentation that has been used and many of the missions that carried out the pioneering observations. Emphasis is given to the historically important early missions even if the results from these have been in some cases bettered by later missions. © 2010 Springer Science+Business Media B.V.
Perri S.,International Space Science Institute |
Balogh A.,International Space Science Institute |
Balogh A.,Imperial College London
Astrophysical Journal | Year: 2010
By using single-point measurements in space physics it is possible to study a phenomenon only as a function of time. This means that we cannot have direct access to information about spatial variations of a measured quantity. However, the investigation of the properties of turbulence and of related phenomena in the solar wind widely makes use of an approximation frequently adopted in hydrodynamics under certain conditions, the so-called Taylor hypothesis; indeed, the solar wind flow has a bulk velocity along the radial direction which is much higher than the velocity of a single turbulent eddy embedded in the main flow. This implies that the time of evolution of the turbulent features is longer than the transit time of the flow through the spacecraft position, so that the turbulent field can be considered frozen into the solar wind flow. This assumption allows one to easily associate time variations with spatial variations and stationarity to homogeneity. We have investigated, applying criteria for weak stationarity to Ulysses magnetic field data in different solar wind regimes, at which timescale and under which conditions the hypothesis of stationarity, and then of homogeneity, of turbulence in the solar wind is well justified. We extend the conclusions of previous studies by Matthaeus & Goldstein to different parameter ranges in the solar wind. We conclude that the stationarity assumption in the inertial range of turbulence on timescales of 10 minutes to 1 day is reasonably satisfied in fast and uniform solar wind flows, but that in mixed, interacting fast, and slow solar wind streams the assumption is frequently only marginally valid. © 2010. The American Astronomical Society. All rights reserved.
News Article | March 14, 2016
Thirty years ago, a European spacecraft completed a pioneering mission for cometary science: Giotto flew by Halley’s Comet, returning the first close-up observations of a comet’s nucleus and paving the way for future cometary exploration such as the ongoing Rosetta mission. “All our understanding of comets when Rosetta was realised in the 90s went back to what we learned from Giotto and to some extent the Vega missions,” said Stephan Ulamec, project manager for Rosetta’s Philae lander, in a phone call. “All of what we produced for engineering models to design the orbiter, to design the lander in particular—all of this goes back to the Giotto mission.” On 13-14 March 1986, the Giotto probe passed by Comet 1P/Halley at a distance of 596 km—thousands of kilometres closer than the two Soviet Vega probes that intercepted Halley earlier in the month—and gave us the first real look at a comet. Giotto gave us the first evidence that comets contained organic material, which is in large part why we’re so interested in them: It’s thought comets could reveal more about the formation of the planets and potentially answer mysteries like how water got to Earth. Giotto’s specific target was suitably worthy. Halley was the first comet to be recognised as “periodic” when Edmond Halley showed in the 18th century that it was reappearing at regular 76-year intervals. But because of this, Giotto was under a big time constraint. “The Giotto mission was started at the end of the 70s with the arrival of Halley’s comet in the vicinity of the Sun a few years later, which left very little time to prepare for an encounter,” recalled astrophysicist Roger-Maurice Bonnet in a phone call. Bonnet was ESA’s director of scientific programmes at the time and now works at the International Space Science Institute at Bern. Originally planned as a joint mission with the US, Giotto became the European Space Agency’s first ever planetary mission when NASA pulled out due to budget cuts. ESA gave the go-ahead in 1980. “It was cheap, it was done fast, it was very risky—we launched a mission with some detectors which had never been flown before in space,” summarised Bonnet. “We had guts to do Giotto.” But Giotto was a success, and its legacy lies in Europe’s continued thirst for cometary exploration and most notably the Rosetta mission, which got even closer to a comet in 2014 when it put an actual lander on the surface of Comet 67P/Churyumov-Gerasimenko. “It triggered the interest in Europe in cometary missions and it triggered the interest to not just have a flyby within hours, but to really visit a comet and observe it over months or even years and land on it,” said Ulamec. The seeds of the Rosetta mission were already being planted before Giotto had returned any data; ESA committed to a “comet nucleus sample return mission” as early as 1984. As the Rosetta mission developed, the team was able to use Giotto's findings to refine its design. Many instruments on Rosetta are specifically looking for the kind of organic chemistry Giotto first found on Halley, and Giotto’s characterisation of the comet’s composition helped inform the design of the Philae lander. Rosetta was launched in 2004 and reached it target 10 years later; the orbiter is still following Comet 67P. The contexts of the Giotto and Rosetta missions differ largely in several ways. For a start, Rosetta’s flyby is more like a slow ride-along; the orbiter is following 67P as the comet develops and even had the chance to drop a lander. Giotto, meanwhile, only got a fleeting glimpse of Halley. Given Halley travels in retrograde (in an opposite direction to the Sun), Giotto and the comet were travelling towards each other at 245,000 km per hour. “In the case of Rosetta, because we were going in the same direction as the comet, we could observe the evolution of the activity of the comet—how the dust was ejected into interplanetary space, how the comet was heated, and whether we could measure the dust particles coming out of the comet,” said Bonnet. “While with Giotto we took the particles in full face, like in a car accident or a plane accident.” A special dust shield kept Giotto safe so it could take pictures of the comet nucleus as it flew by, and indeed the spacecraft not only survived the journey but lived to go into hibernation for a couple extra missions, such as a flyby of Comet Grigg-Skjellerup in 1992. Rosetta still has months left before its mission ends with a dive into its target comet, but its legacy clearly carries on the work of its comet-chasing forefather. “Both missions are landmarks in the history of the evolution of the Solar System,” said Bonnet. “There will be others in the future, but certainly both of them have made history when they obtained their first results.”