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Register a new userDARWIN - A Mission to Detect, and Search for Life on, Extrasolar Planets
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The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. The detection of planets with a wide range of masses demonstrates that extra-solar planets of low mass exist. In this paper we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines including astrophysics, planetary sciences, chemistry and microbiology. Darwin is designed to detect and perform spectroscopic analysis of rocky planets similar to the Earth at mid-infrared wavelengths (6 - 20 micron), where an advantageous contrast ratio between star and planet occurs. The baseline mission lasts 5 years and consists of approximately 200 individual target stars. Among these, 25 to 50 planetary systems can be studied spectroscopically, searching for gases such as CO2, H2O, CH4 and O3. Many of the key technologies required for the construction of Darwin have already been demonstrated and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.
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The discovery of extra-solar planets is one of the greatest achievements of modern astronomy. There are now more than 200 such objects known, and the recent detection of planets with masses approximately 5 times that of Earth demonstrates that extra-solar planets of low mass exist. In addition to providing a wealth of scientific information on the formation and structure of planetary systems, these discoveries capture the interest of both scientists and the wider public with the profound prospect of the search for life in the Universe. We propose an L-type mission, called Darwin, whose primary goal is the study of terrestrial extrasolar planets and the search for life on them. By its very nature, Darwin advances the first Grand Theme of ESA Cosmic Vision. Accomplishing the mission objectives will require collaborative science across disciplines ranging from planet formation and atmospheres to chemistry and biology, and these disciplines will reap profound rewards from their contributions to the Darwin mission.
We report spectroscopic observations (400 to 800nm, R = approx 100) of Earthshine in June, July and October 2001 from which normalised Earth albedo spectra have been derived. The resulting spectra clearly show the blue colour of the Earth due to Rayleigh diffusion in its atmosphere. They also show the signatures of oxygen, ozone and water vapour. We tried to extract from these spectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%) around 700nm has been measured in the Earth albedo. It is interpreted as being due to the vegetation red edge, expected to be between 2 to 10% of the Earth albedo at 700nm, depending on models. We discuss the primary goal of the present observations: their application to the detection of vegetation-like biosignatures on extrasolar planets.
Due to their extremely small luminosity compared to the stars they orbit, planets outside our own Solar System are extraordinarily difficult to detect directly in optical light. Careful photometric monitoring of distant stars, however, can reveal the presence of exoplanets via the microlensing or eclipsing effects they induce. The international PLANET collaboration is performing such monitoring using a cadre of semi-dedicated telescopes around the world. Their results constrain the number of gas giants orbiting 1--7 AU from the most typical stars in the Galaxy. Upgrades in the program are opening regions of ``exoplanet discovery space -- toward smaller masses and larger orbital radii -- that are inaccessible to the Doppler velocity technique.
We present an analytic model to estimate the capabilities of space missions dedicated to the search for biosignatures in the atmosphere of rocky planets located in the habitable zone of nearby stars. Relations between performance and mission parameters such as mirror diameter, distance to targets, and radius of planets, are obtained. Two types of instruments are considered: coronagraphs observing in the visible, and nulling interferometers in the thermal infrared. Missions considered are: single-pupil coronagraphs with a 2.4 m primary mirror, and formation flying interferometers with 4 x 0.75 m collecting mirrors. The numbers of accessible planets are calculated as a function of {eta}earth. When Kepler gives its final estimation for {eta}earth, the model will permit a precise assessment of the potential of each instrument. Based on current estimations, {eta}earth = 10% around FGK stars and 50% around M stars, the coronagraph could study in spectroscopy only ~1.5 relevant planets, and the interferometer ~14.0. These numbers are obtained under the major hypothesis that the exozodiacal light around the target stars is low enough for each instrument. In both cases, a prior detection of planets is assumed and a target list established. For the long-term future, building both types of spectroscopic instruments, and using them on the same targets, will be the optimal solution because they provide complementary information. But as a first affordable space mission, the interferometer looks the more promising in term of biosignature harvest.
In order to evaluate and develop mission concepts for a search for Terrestrial Exoplanets, we have prepared a list of potential target systems. In this paper we present and discuss the criteria for selecting potential target stars suitable for the search for Earth like planets, with a special emphasis on the aspects of the habitable zone for these stellar systems. Planets found within these zones would be potentially able to host complex life forms. We derive a final target star sample of potential target stars, the Darwin All Sky Star Catalog (DASSC). The DASSC contains a sample of 2303 identified objects of which 284 are F, 464 G, 883 K, 615 M type stars and 57 stars without B-V index. Of these objects 949 objects are flagged in the DASSC as multiple systems, resulting in 1229 single main sequence stars of which 107 are F, 235 are G, 536 are K, and 351 are M type. We derive configuration dependent subcatalogs from the DASSC for two technical designs, the initial baseline design and the advanced Emma design as well as a catalog using an inner working angle cut off. We discuss the selection criteria, derived parameters and completeness of sample for different classes of stars.
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