| 1. |
- Lammer, H., et al.
(författare)
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Geophysical and Atmospheric Evolution of Habitable Planets
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 45-68
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.
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| 2. |
- Rauer, H., et al.
(författare)
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The PLATO 2.0 mission
- 2014
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 38:1-2, s. 249-330
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Tidskriftsartikel (refereegranskat)abstract
- PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 s readout cadence and 2 with 2.5 s cadence) providing a wide field-of-view (2232 deg(2)) and a large photometric magnitude range (4-16 mag). It focuses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50 % of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. The PLATO 2.0 catalogue allows us to e. g.: - complete our knowledge of planet diversity for low-mass objects, - correlate the planet mean density-orbital distance distribution with predictions from planet formation theories,- constrain the influence of planet migration and scattering on the architecture of multiple systems, and - specify how planet and system parameters change with host star characteristics, such as type, metallicity and age. The catalogue will allow us to study planets and planetary systems at different evolutionary phases. It will further provide a census for small, low-mass planets. This will serve to identify objects which retained their primordial hydrogen atmosphere and in general the typical characteristics of planets in such a low-mass, low-density range. Planets detected by PLATO 2.0 will orbit bright stars and many of them will be targets for future atmosphere spectroscopy exploring their atmospheres. Furthermore, the mission has the potential to detect exomoons, planetary rings, binary and Trojan planets. The planetary science possible with PLATO 2.0 is complemented by its impact on stellar and galactic science via asteroseismology as well as light curves of all kinds of variable stars, together with observations of stellar clusters of different ages. This will allow us to improve stellar models and study stellar activity. A large number of well-known ages from red giant stars will probe the structure and evolution of our Galaxy. Asteroseismic ages of bright stars for different phases of stellar evolution allow calibrating stellar age-rotation relationships. Together with the results of ESA's Gaia mission, the results of PLATO 2.0 will provide a huge legacy to planetary, stellar and galactic science.
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| 3. |
- Brunkwall, J., et al.
(författare)
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Endovascular Repair of Acute Uncomplicated Aortic Type B Dissection Promotes Aortic Remodelling: 1 Year Results of the ADSORB Trial
- 2014
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1532-2165 .- 1078-5884. ; 48:3, s. 285-291
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Uncomplicated acute type B aortic dissection (AD) treated conservatively has a 10% 30-day mortality and up to 25% need intervention within 4 years. In complicated AD, stent grafts have been encouraging. The aim of the present prospective randomised trial was to compare best medical treatment (BMT) with BMT and Gore TAG stent graft in patients with uncomplicated AD. The primary endpoint was a combination of incomplete/no false lumen thrombosis, aortic dilatation, or aortic rupture at 1 year. Methods: The AD history had to be less than 14 days, and exclusion criteria were rupture, impending rupture, malperfusion. Of the 61 patients randomised, 80% were DeBakey type IIIB. Results: Thirty-one patients were randomised to the BMT group and 30 to the BMT+TAG group. Mean age was 63 years for both groups. The left subclavian artery was completely covered in 47% and in part in 17% of the cases. During the first 30 days, no deaths occurred in either group, but there were three crossovers from the BMT to the BMT TAG group, all due to progression of disease within 1 week. There were two withdrawals from the BMT+TAG group. At the 1-year follow up there had been another two failures in the BMT group: one malperfusion and one aneurysm formation (p = .056 for all). One death occurred in the BMT TAG group. For the overall endpoint BMT+TAG was significantly different from BMT only (p < .001). Incomplete false lumen thrombosis, was found in 13 (43%) of the TAG+BMT group and 30 (97%) of the BMT group (p < .001). The false lumen reduced in size in the BMT+TAG group (p < .001) whereas in the BMT group it increased. The true lumen increased in the BMT TAG (p < .001) whereas in the BMT group it remained unchanged. The overall transverse diameter was the same at the beginning and after 1 year in the BMT group (42.1 mm), but in the BMT+TAG it decreased (38.8 mm; p = .062). Conclusions: Uncomplicated AD can be safely treated with the Gore TAG device. Remodelling with thrombosis of the false lumen and reduction of its diameter is induced by the stent graft, but long term results are needed. (C) 2014 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.
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| 4. |
- Malbet, F., et al.
(författare)
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High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)
- 2012
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 34:2, s. 385-413
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Tidskriftsartikel (refereegranskat)abstract
- A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood (d a parts per thousand currency signaEuro parts per thousand 15 pc) with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT-the Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne extremely-high-precision astrometric measurements at the 0.05 mu as (1 sigma) accuracy level, sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth's around the nearest stars. Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit. The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field. The NEAT instrument design consists of an off-axis parabola single-mirror telescope (D = 1 m), a detector with a large field of view located 40 m away from the telescope and made of 8 small movable CCDs located around a fixed central CCD, and an interferometric calibration system monitoring dynamical Young's fringes originating from metrology fibers located at the primary mirror. The mission profile is driven by the fact that the two main modules of the payload, the telescope and the focal plane, must be located 40 m away leading to the choice of a formation flying option as the reference mission, and of a deployable boom option as an alternative choice. The proposed mission architecture relies on the use of two satellites, of about 700 kg each, operating at L2 for 5 years, flying in formation and offering a capability of more than 20,000 reconfigurations. The two satellites will be launched in a stacked configuration using a Soyuz ST launch vehicle. The NEAT primary science program will encompass an astrometric survey of our 200 closest F-, G- and K-type stellar neighbors, with an average of 50 visits each distributed over the nominal mission duration. The main survey operation will use approximately 70% of the mission lifetime. The remaining 30% of NEAT observing time might be allocated, for example, to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest (low-mass stars, young stars, etc.) discovered by Gaia, ground-based high-precision radial-velocity surveys, and other programs. With its exquisite, surgical astrometric precision, NEAT holds the promise to provide the first thorough census for Earth-mass planets around stars in the immediate vicinity of our Sun.
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| 5. |
- Brain, D., et al.
(författare)
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A comparison of global models for the solar wind interaction with Mars
- 2010
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 206:1, s. 139-151
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Tidskriftsartikel (refereegranskat)abstract
- We present initial results from the first community-wide effort to compare global plasma interaction model results for Mars. Seven modeling groups participated in this activity, using MHD, multi-fluid, and hybrid assumptions in their simulations. Moderate solar wind and solar EUV conditions were chosen, and the conditions were implemented in the models and run to steady state. Model output was compared in three ways to determine how pressure was partitioned and conserved in each model, the location and asymmetry of plasma boundaries and pathways for planetary ion escape, and the total escape flux of planetary oxygen ions. The two participating MHD models provided similar results, while the five sets of multi-fluid and hybrid results were different in many ways. All hybrid results, however, showed two main channels for oxygen ion escape (a pickup ion 'plume' in the hemisphere toward which the solar wind convection electric field is directed, and a channel in the opposite hemisphere of the central magnetotail), while the MHD models showed one (a roughly symmetric channel in the central magnetotail). Most models showed a transition from an upstream region dominated by plasma dynamic pressure to a magnetosheath region dominated by thermal pressure to a low altitude region dominated by magnetic pressure. However, calculated escape rates for a single ion species varied by roughly an order of magnitude for similar input conditions, suggesting that the uncertainties in both the current and integrated escape over martian history as determined by models are large. These uncertainties are in addition to those associated with the evolution of the Sun, the martian dynamo, and the early atmosphere, highlighting the challenges we face in constructing Mars' past using models.
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| 6. |
- Grenfell, J. L., et al.
(författare)
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Co-Evolution of Atmospheres, Life, and Climate
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 77-88
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Tidskriftsartikel (refereegranskat)abstract
- After Earth's origin, our host star, the Sun, was shining 20-25% less brightly than today. Without greenhouse-like conditions to warm the atmosphere, our early planet would have been an ice ball, and life may never have evolved. But life did evolve, which indicates that greenhouse gases must have been present on early Earth to warm the planet. Evidence from the geological record indicates an abundance of the greenhouse gas CO2. CH4 was probably present as well; and, in this regard, methanogenic bacteria, which belong to a diverse group of anaerobic prokaryotes that ferment CO2 plus H-2 to CH4, may have contributed to modification of the early atmosphere. Molecular oxygen was not present, as is indicated by the study of rocks from that era, which contain iron carbonate rather than iron oxide. Multicellular organisms originated as cells within colonies that became increasingly specialized. The development of photosynthesis allowed the Sun's energy to be harvested directly by life-forms. The resultant oxygen accumulated in the atmosphere and formed the ozone layer in the upper atmosphere. Aided by the absorption of harmful UV radiation in the ozone layer, life colonized Earth's surface. Our own planet is a very good example of how life-forms modified the atmosphere over the planets' lifetime. We show that these facts have to be taken into account when we discover and characterize atmospheres of Earth-like exoplanets. If life has originated and evolved on a planet, then it should be expected that a strong co-evolution occurred between life and the atmosphere, the result of which is the planet's climate.
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| 7. |
- Alibert, Y., et al.
(författare)
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Origin and Formation of Planetary Systems
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 19-32
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Tidskriftsartikel (refereegranskat)abstract
- To estimate the occurrence of terrestrial exoplanets and maximize the chance of finding them, it is crucial to understand the formation of planetary systems in general and that of terrestrial planets in particular. We show that a reliable formation theory should not only explain the formation of the Solar System, with small terrestrial planets within a few AU and gas giants farther out, but also the newly discovered exoplanetary systems with close-in giant planets. Regarding the presently known exoplanets, we stress that our current knowledge is strongly biased by the sensitivity limits of current detection techniques (mainly the radial velocity method). With time and improved detection methods, the diversity of planets and orbits in exoplanetary systems will definitely increase and help to constrain the formation theory further. In this work, we review the latest state of planetary formation in relation to the origin and evolution of habitable terrestrial planets.
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| 8. |
- Brack, A., et al.
(författare)
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Origin and Evolution of Life on Terrestrial Planets
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- The ultimate goal of terrestrial planet-finding missions is not only to discover terrestrial exoplanets inside the habitable zone (HZ) of their host stars but also to address the major question as to whether life may have evolved on a habitable Earth-like exoplanet outside our Solar System. We note that the chemical evolution that finally led to the origin of life on Earth must be studied if we hope to understand the principles of how life might evolve on other terrestrial planets in the Universe. This is not just an anthropocentric point of view: the basic ingredients of terrestrial life, that is, reduced carbon-based molecules and liquid H2O, have very specific properties. We discuss the origin of life from the chemical evolution of its precursors to the earliest life-forms and the biological implications of the stellar radiation and energetic particle environments. Likewise, the study of the biological evolution that has generated the various life-forms on Earth provides clues toward the understanding of the interconnectedness of life with its environment.
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| 9. |
- Dvorak, R., et al.
(författare)
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Dynamical Habitability of Planetary Systems
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 33-43
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Tidskriftsartikel (refereegranskat)abstract
- The problem of the stability of planetary systems, a question that concerns only multiplanetary systems that host at least two planets, is discussed. The problem of mean motion resonances is addressed prior to discussion of the dynamical structure of the more than 350 known planets. The difference with regard to our own Solar System with eight planets on low eccentricity is evident in that 60% of the known extrasolar planets have orbits with eccentricity e > 0.2. We theoretically highlight the studies concerning possible terrestrial planets in systems with a Jupiter-like planet. We emphasize that an orbit of a particular nature only will keep a planet within the habitable zone around a host star with respect to the semimajor axis and its eccentricity. In addition, some results are given for individual systems (e.g., Gl777A) with regard to the stability of orbits within habitable zones. We also review what is known about the orbits of planets in double-star systems around only one component ( e. g., gamma Cephei) and around both stars (e.g., eclipsing binaries).
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| 10. |
- Fridlund, M., et al.
(författare)
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A Roadmap for the Detection and Characterization of Other Earths
- 2010
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 10:1, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- The European Space Agency and other space agencies such as NASA recognize that the question with regard to life beyond Earth in general, and the associated issue of the existence and study of exoplanets in particular, is of paramount importance for the 21(st) century. The new Cosmic Vision science plan, Cosmic Vision 2015-2025, which is built around four major themes, has as its first theme: "What are the conditions for planet formation and the emergence of life?'' This main theme is addressed through further questions: (1) How do gas and dust give rise to stars and planets? (2) How will the search for and study of exoplanets eventually lead to the detection of life outside Earth (biomarkers*)? (3) How did life in the Solar System arise and evolve? Although ESA has busied itself with these issues since the beginning of the Darwin study in 1996, it has become abundantly clear that, as these topics have evolved, only a very large effort, addressed from the ground and from space with the utilization of different instruments and space missions, can provide the empirical results required for a complete understanding. The good news is that the problems can be addressed and solved within a not-too-distant future. In this short essay, we present the present status of a roadmap related to projects that are related to the key long-term goal of understanding and characterizing exoplanets, in particular Earthlike planets.
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