100 CLEFS CEA - No. 58 - AUTUMN 2009 Proto-Jupiter, embedded in its protoplanetary disk. The protoplanet is setting up a one-armed spiral wake, voiding a gap around its own orbit. On the heels of instrumentation, and observation, simulation is the third path taken by research in astrophysics. The goal set for the COAST project is the modeling of complex astrophysical phenomena, to corroborate current theories on the physics of celestial objects, and lay the ground for future astronomical observations. The chief areas of study benefiting from this project are cosmology, stellar physics, the investigation of protoplanetary disks, and that of the interstellar medium. Protoplanetary disks: the FARGO (2-D) and JUPITER (3-D) codes are used to describe, across a grid, the evolution of the gas making up the protoplanetary nebula. F.Masset/CEA II. TOOLS TO PROBE THE UNIVERSE How is the mass distribution of stars to be accounted for? How do galaxies end their existence? What is the cause of the acceleration in the expansion of the Universe? In their endeavor to resolve these issues, astrophysicists are developing a new generation of revolutionary telescopes, providing the ability to see further, more precisely, and with a wider field of view than their predecessors. These telescopes, whether ground-based or out in space, will collect light that is to be analyzed, in minutest detail, by instruments that are the embodiment of leading-edge detection technology. Affording as they do the ability to yield very finely detailed images, while carrying out spectrometry of remarkable quality, these highly sophisticated instruments known as “imaging spectrometers” stand as one of CEA’s proven areas of excellence. Their remit? To collect the information sent out by cosmic sources, so that this may be converted into digital signals, subsequently subjected to a variety of data processing methods. Such methods are currently undergoing spectacular developments. Thereafter, it will be the astrophysicists’ task to analyze the results thus obtained. To ensure their ability to do this, researchers are turning to numerical simulations of the Universe and of the objects in it, carried out on massively parallel supercomputers. Thus, the age-old scientific diptych, “theory–observation,” has been enriched by the intervention of a new tool, numerical simulation – coming in as the bridging link between ever more complex theoretical models and yet indispensable observation. Of the outcome of such work, research scientists anticipate it may yield the corroboration, or invalidation, of their present knowledge of the Universe. CLEFS CEA - No. 58 - AUTUMN 2009 101 Tools to probe the Universe Telescopes of the future While astrophysicists have shed completely new light on our knowledge of the Solar System, and while they have detected some 400 exoplanets; and even though the expansion of the Universe is fully confirmed by observation, and even though telescopes are able to probe almost to the confines of the Universe, into the regions where the first stars, and galaxies were born… Yet major issues do still stand, while new issues have arisen, e.g. the origin of the acceleration currently found in the expansion of the Universe, which, as yet, presents a major conundrum. This is what has led to the emergence of a new generation of telescopes, affording the ability to observe the cosmos further out, more precisely, and providing a wider view. 1. Seeing further out JWST : looking back on a past 13 billion years old NASA Artist’s impression of JWST, in folded configuration inside its shroud, atop the Ariane 5 launcher (at left), and unfurled in space (right panel), in which configuration, aside from the primary mirror (gold), the thermal shields (blue) may be seen, these preventing the Sun’s rays from heating the telescope. t the present time, the Hubble Space Telescope telescope will have the ability to observe the Universe A (HST) still stands as one of the most stupendous as it stood 13 billion years ago, at the time when the observatories ever, the source of an impressive number first stars were formed. of discoveries. Nevertheless, featuring as it does a tele- This is a NASA program, with contributions from scope with a diameter no larger than 2.4 meters, it is Europe, and Canada. Working in partnership with unable to detect the faint glimmer that is received CNES, CEA, acting through the Astrophysics Service from the most distant cosmic objects. Achieving such (SAp) at the Institute of Research into the Fundamental capability would call for the design, and construction Laws of the Universe (IRFU), will be taking on two of a telescope featuring a larger collecting area, affor- major responsibilities: first of all, steering the French ding the ability to observe infrared (IR) light – the contribution to the Mid-Infrared Instrument (MIRI), visible light emitted by a very distant object, in an one of the four onboard instruments carried by JWST, expanding Universe, being shifted to the infrared, for an observer. Thus arose the concept of the James Webb (1) Space Telescope (JWST), to provide a successor to (1) So named to commemorate NASA’s second administrator, HST. With its 6.5-meter diameter mirror, the new James E. Webb (1906–92). 102 CLEFS CEA - No. 58 - AUTUMN 2009 dedicated to observation of cosmic infrared radia- tion in the 5–28 micrometer wavelength range; second, responsibility for the planned Expertise Center, to be based in France, which will be dedicated to analysis of the data collected by MIRI. JWST is due to be placed in orbit, in 2014, by an Ariane 5 launcher, the only launcher having the ability to cater for such a giant. As the volume provided by the shroud featured by the Ariane 5 launcher is insuf- ficient to accommodate the new telescope, it will be launched in folded configuration, being deployed only once out in space. Owing to major technological developments, it proved feasible to make substantial weight savings on the device as a whole. Thus, despite a diameter nearly three times larger than that of its predecessor, HST, JWST will weigh in at 6.5 tonnes, i.e. half the mass of its forerunner. There remained one further, major constraint to square, for engineers. Dedicated as it is to the detection of cosmic infrared radiation, JWST will be operating at temperatures of about –220 °C, to preclude its own light emission interfering with its observations of the cosmos. This was the reason for the decision to position JWST at NASA Lagragian point L2, lying 1.5 million kilometers away Full-scale mockup of JWST. from the Earth (see Figure 1), by contrast to the posi- tion of HST, in low orbit, a mere 600 km or so from (ESO) Very Large Telescope (VLT), in Chile. This state the Earth. Given the distance, there can be no ques- of affairs resulted in SAp taking on the scientific, and tion of going out to repair the telescope, should a technical leadership, for the MIRI imager.(2) Aside problem arise! from IRFU, three other French laboratories are Three main instruments will be positioned at the involved in this project – namely, the Space Research focus of JWST, to capture the light concentrated by and Astrophysical Instrumentation Laboratory the telescope, and turn it into a digital signal, sent (LESIA: Laboratoire d’études spatiales et d’instru- back to Earth: mentation en astrophysique), at the Paris–Meudon • the Near-Infrared Camera (NIRCAM), a camera Observatory; the Space Astrophysics Institute (IAS: for the near infrared (1–5 micrometers), designed, Institut d’astrophysique spatiale), at Orsay (near and constructed in the United States; Paris); and the Marseille Astrophysics Laboratory • the Near-Infrared Spectrometer (NIRSPEC), a spec- (LAM). CNES – also a CEA partner for this program trometer, likewise dedicated to the near infrared, designed, and constructed by European manufactu- (2) Aside from SAp, other services at IRFU are taking part in the rers, under project leadership, and with funding, from project: the Detector Electronics and Informatics Service (SEDI); the European Space Agency (ESA); the Systems Engineering Service (SIS); and the Accelerators, Cryogenics, and Magnetism Service (SACM). • the Mid-Infrared Instrument (MIRI), an imaging spectrometer for the mid-infrared (5–27 microme- ters), designed, and constructed by a collaboration, one half being accounted for by the United States (Jet Propulsion Laboratory/NASA), the other half by a consortium of space laboratories, from 10 countries (by decreasing rank, in terms of funds contributed: the United Kingdom, France, Belgium, the Netherlands, Germany, Spain, Switzerland, Sweden, Denmark, Sun Ireland), led by the UK’s Royal Observatory, Edinburgh (ROE), and funded by the respective Moon Earth national agencies. 150 million km It should be pointed out that, initially, the JWST program had made no provisions for a dedicated instrument for mid-infrared observation. In the late 1990s, only a small band of US, and European astro- 1.5 million km physicists advocated the presence of such an instru- ment, in the proposed space telescope. This prescient L2 advance guard included, in particular, astrophysicists at CEA, aware as they were of the potentialities of this type of instrument, and already heavily involved in observations of the mid-infrared – e.g. with the ISOCAM camera, sent out in space in 1995, or the VISIR (VLT Imager and Spectrometer in Infrared) Figure 1. instrument for the European Southern Observatory’s Schematic showing the location of Lagrangian point L2, around which JWST will be positioned. CLEFS CEA - No. 58 - AUTUMN 2009 103 Tools to probe the Universe L. Godart/CEA The Mid-Infrared Imager (MIRIM) camera, due to be mounted in JWST, being inspected, under ultraviolet light, to check no particulate contamination has occurred. – is contributing 50% of program funding (including will subsequently integrate the instrument into JWST, workforce costs).