ESA's Cosmic Vision: Europe is narrowing the choices for the next round of space science missions.

Following a mid-October meeting of the European Space Agency's Space Science Advisory Committee (SSAC), candidate missions for ESA's Cosmic Vision 2015-2025 plan have been selected for further assessment and consideration for launch in 2017/2018. The selected candidate missions include four astrophysics missions--a dark energy mission (Dune or Space), a planet-finder mission (Plato), a space infrared telescope (Spica) and an X-ray space observatory Xeus). Also under consideration are four solar system exploration missions to study satellites of Jupiter and Saturn (Laplace and Tandem), space plasmas (Cross-Scale) and a near-Earth object (Marco Polo). These new candidate missions are joined by the Laser Interferometer Space Antenna (Lisa) mission, which was moved into the Cosmic Vision 2015-2025 plan in May 2007.

The new missions are scheduled to follow on from those being developed under the current phase of the Cosmic Vision programme--Herschel and Planck (due to be launched in July 2008), the Gala astronomy satellite (2009), the BepiColombo probe to Mercury (2013), participation in the James Webb Space Telescope (2013) and the Solar Orbiter probe (2015).

At the end of the selection process, the Agency will pick one Medium mission (350 million [euro]) for a launch in 2017 and one Large mission (600 million [euro]), to be launched in 2018. The total cost should be compared with the total ESA science budget of around 400 million [euro] per year. The candidate Large missions are Xeus, Laplace, Tandem, and Lisa; all the others are considered Medium missions, with the exception of Spica, which is classified as an "Opportunity" mission in view of its low budget (less than l00 million [euro]).

Two proposals have been received for the study of dark matter and dark energy--the Dark UNiverse Explorer (DUNE) and the SPectroscopic All-sky Cosmic Explorer (SPACE). While they propose to use different techniques (DUNE is proposed as a wide-field imager, while SPACE is proposed as a near-infrared all-sky surveyor), they address the same basic science goal. In the follow-up study phase a trade-off will be performed leading to the definition in the spring of next year of a proposal for a European dark energy mission to go forward in competition.

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DUNE mission

The purpose of the DUNE mission is to shed light on the dark components of the Universe with a wide field imager in space. To study the dark Universe, DUNE will make use of the weak gravitational lensing effect which provides a direct measure of the distribution of dark matter in the Universe. This is done by measuring the weak distortions induced by intervening large-scale structures on the images of distant galaxies. This can be used to measure cosmological parameters, and, in particular, the dark energy equation-of-state parameter which affects the growth of cosmic structures. The wide-field imager of DUNE will circumvent atmospheric effects, which limit ground based surveys, and provide both high statistics (i.e. more resolved galaxies) and low systematics (thanks to a small and stable PSF) for weak lensing. Another method which will be used to probe dark energy is provided by Supernovae Ia, a homogeneous class of objects which have been shown to provide excellent distance indicators. With its panoramic wide field surveys, DUNE will also provide a wealth of astrophysical insights into the formation of galaxies, the study of galaxy clusters, type II supernovae, baryonic acoustic oscillations, and allow fundamental tests of the theory of gravity on large scales.

Reduced risk and costs

The baseline concept developed during the CNES phase 0 consists of a 1.2m telescope with a 0.5 square degree optical CCD camera. It is designed to be fast with reduced risks and costs, and to take advantage of the synergy between ground-based and space observations. Stringent requirements for weak lensing systematics were shown to be achievable with the baseline concept. This will allow DUNE to place strong constraints on cosmological parameters, including the equation of state parameter of the dark energy and its evolution from red-shift 0 to 1.

The proposed next-generation planet finder--PLAnetary Transits and Oscillations of stars (Plato) is a photometry mission that will detect and characterise transiting exoplanets as well as measure the seismic oscillations of their parent stars. It will be capable of observing rocky exoplanets around brighter and better characterized stars than its predecessors. Observations of the mission will be complemented by ground- and space-based follow-up observations to derive the planet's masses and study their atmospheres.

Plato will detect and characterize exoplanets by means of their transit signature in front of a very large sample of bright stars, and measure the seismic oscillations of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems. Plato is the next-generation planet finder, building on the accomplishments of CoRoT and Kepler. Features compared with earlier missions include: observation of significantly more stars; stars will be three magnitudes brighter (hence the precision of the measurements will be correspondingly greater as will be those of post- detection investigations, e.g. spectroscopy, asteroseismology, and eventually imaging); capability to observe significantly smaller exoplanets with significantly longer orbital periods. The space- based observations will be complemented by ground- and space-based follow-up observations; for instance spectroscopic measurements of radial velocities of the detected exoplanetary systems will be obtained to derive the planet masses; differential visible and infrared spectroscopy during and outside secondary transit will also be performed, in particular with JWST, in order to derive information on the exoplanet atmospheres.

100 telescopes

Two different mission concepts are being proposed: a "staring" concept and a "spinning" concept. The "staring concept" utilizes 100 telescopes each with its own CCD focal plane, comprised of 24 CCDs with 800 x 1800 pixels, operated in full-frame mode, which monitors the same field for the entire mission, i.e. up to five years. The satellite is three-axis stabilized and uses a Planck-Herschel recurrent platform. The "spinning" concept uses a Gala platform, and three identical 0.72 [m.sup.2] telescopes, pointing 120[degrees] from one another, sweep out a great circle on the sky perpendicular to the spin axis. The payload would also be used half of the time in a fine-pointing mode, during which the spacecraft is three-axis stabilized. The focal plane of each telescope is made up of 32 Gaia-type CCDs operated in TDI mode in the spinning phases and in frame transfer mode in the pointed phases.

The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a proposed medium- and far-infrared observatory with a large-aperture cryogenic telescope. The mission would address planetary formation, the way the solar system works and the origin of the universe. It would perform wide-field, high-sensitivity photometric mapping at high spatial resolution, spectral analysis as well as coronography of planets and planetary disks. SPICA is proposed in collaboration with the Japanese Aerospace Exploration Agency, JAXA, with ESA providing the telescope and a contribution to the operations.

The X-ray Evolving Universe Spectroscopy (XEUS) is a next-generation X-ray space observatory to study the fundamental laws of the Universe and the origins of the universe. With unprecedented sensitivity to the hot. million-degree universe. XEUS would explore key areas of contemporary astrophysics: growth of supermassive black holes, cosmic feedback and galaxy evolution, evolution of large-scale structures, extreme gravity and matter under extreme conditions, the dynamical evolution of cosmic plasmas and cosmic chemistry. XEUS would be stationed in a halo orbit at L2, the second Lagrange point, with two satellites (one mirror satellite and the other a detector satellite) that would fly in formation.

Various international partners have expressed interest in cooperation in XEUS and discussions will start by the end of the year with the interested agencies to ensure the earliest involvement in study work.

Cross-Scale mission

The candidate Solar System missions include the Cross-Scale mission to investigate multi-scale coupling in space plasmas. Cross-Scale would employ 12 spacecraft to make simultaneous measurements of plasma on different scales at shocks, reconnection sites, and turbulent regions in near-Earth space. It will address fundamental questions such as how shocks accelerate and heat particles or how magnetic reconnection phenomena generate or convert energy. If approved, the mission would be implemented in collaboration with JAXA, the Japanese space and exploration agency. Marco Polo is a near-Earth object (NEO) sample-return mission that would characterise a NEO at multiple scales and return a sample. If approved, the mission would study the origins and evolution of the Solar System, the role of minor bodies in the process, origins and evolution of Earth and of life itself. It would consist of a mother satellite which would carry a lander, sampling devices, reentry capsule as well as instruments. If approved, the mission would be implemented in collaboration with JAXA and possibly combined with the Hayabusa Mark 2 mission

Jovian system