The paper focuses on the issues for detection of life by remote observations. The problem is divided into the detection of terrestrial planets and the detection of life on them. The problem of detection of planets is compared with the observations of the Hubble Deep Field. The difficulty of detection will likely result in many interesting discoveries before detection techniques are adequate. It is proposed that life is the activity of mutually assisting persistence processes. A persistence process is one that uses the Gibbs Free Energy of the environment for repair and development. It is pointed out that because life produces approximations to equilibrium it is intrinsically difficult to detect by remote observations. Chemical signs of life will be distinctive if the abiotic processes that might produce them are implausible, and preferably absent. The ease of remote detection of terrestrial life is contrasted with problems likely to arise for other planets. It is recommended that initial searches be focused on giant planets. The spectral region of the discovery observations will be set by technical issues which are not yet resolved for any technique. For determining whether life is present, as many spectral regions as possible should be observed.

We present simulations which demonstrate to which extent mid-infrared images and millimeter maps can be used to trace the location of giant planets in circumstellar disks. The most promising approach is to look for characteristic signatures in circumstellar disks caused by the interaction of giant planets with the disk. Numerical simulations show that these signatures are usually in size much larger than the planet itself and thus much easier to detect. The particular result of the planet-disk-interaction depends on the evolutionary stage of the disk. Primary signatures of planets embedded in disks are gaps in the case of young disks and characteristic asymmetric density patterns in debris disks. Radiative transfer simulations predict that high spatial resolution observations performed with instruments/telescopes that will become available in the near future will allow to trace the formation and evolution of planets in protoplanetary and debris disks.

Here we examine the visible spectra of giant planets in anticipation of the science return of missions like the Terrestrial Planet Finder-Coronagraph and proposed Discovery class space coronagraph missions EPIC and ECLIPSE. Our understanding of extrasolar giant planets is already greatly improving because of our studies of old brown dwarfs (which have effective temperatures similar to young giant planets), transiting hot Jupiters, and the planet Jupiter itself. The first data collected on Jupiter-like extrasolar giant planets will likely consist of magnitudes in a few filters or very low resolution spectra. We investigate diagnostics for determining planetary effective temperature, atmospheric chemical abundances, cloud cover, and mass using such limited data. In general, giant planet science is improved significantly if missions in the visible domain extend to wavelengths as long as possible, within engineering constraints.

The phase or orbital light curves of extrasolar terrestrial planets in reflected or emitted light will contain information about their atmospheres and surfaces complementary to data obtained by other techniques such as spectrosopy. We show calculated light curves at optical and thermal infrared wavelengths for a variety of Earth-like and Earth-unlike planets. We also show that large satellites of Earth-sized planets are detectable, but may cause aliasing effects if the lightcurve is insufficiently sampled.

This paper presents the scientific case for a next generation adaptive optics instrument at the VLT, temporarily named “Planet Finder”, that is aimed at detecting and characterizing extrasolar planets through the direct analysis of their emitted photons in the visible and at near-IR wavelengths. We discuss the observational niche of such an instrument to have first light in 2010, in complement to other planet search methods. To improve the efficiency (and consistency) of the search for planets with the PF, the observations will need to be organized in the form of an extensive survey of hundreds of nearby stars, predicted outputs of which are also described here. This summarizes the study phase of the instrument, conducted by two competitive teams and the recent merging of both studies, regarding the scientific impact of Planet Finder.

Light reflected from planets is polarized. This basic property of planets provides the possibility for detecting and characterizing extra-solar planets using polarimetry. The expected polarization properties of extra-solar planets are discussed that can be inferred from polarimetry of “our” solar system planets. They show a large variety of characteristics depending on the atmospheric and/or surface properties. Best candidates for a polarimetric detection are extra-solar planets with an optically thick Rayleigh scattering layer.

Even the detection of highly polarized extra-solar planets requires a very sophisticated instrument. We present the results from a phase A (feasibility) study for a polarimetric arm in the ESO VLT planet finder instrument. It is shown that giant planets around nearby stars can be searched and investigated with an imaging polarimeter, combined with a powerful AO system and a coronagraph at an 8 m class telescope.

A similar type of polarimeter is also considered for the direct detection of terrestrial planets using an AO system on one of the future Extremely Large Telescopes.

In our search for clues as to the nature of the exosphere of HD209458 (Moutou et al., 2001 ; Moutou et al., 2003, Iro et al., 2004), we have acquired VLT/UVES data during an ambitious observational campaign performed in June-September 2002 and covering 6 transits of the exoplanet. The resolving power was R=100000 in the 0.475-0.68 micron range. We search for ions and neutral molecules (such as H2O+, CO+, CH+, etc) originating in the planets exosphere and located in the evaporated material around the planet, occulting its primary star. We present in this paper a tentative search in the spectral regions where features of sodium or H$_2$O$^+$ can be present.

Radial velocity surveys provide evidence that giant extrasolar planets are common, but their detection space is limited to only a few astronomical units from the stars. In order to close this gap, the adaptive optics assisted NIR imager NAOS-CONICA (NACO) at the VLT was used for a deep (15-20 minutes exposure time per target) L-band survey of a sample of closeby young stars. All stars are members of the Tucana and $\beta$ Pictoris moving groups apart from the the somewhat older star HIP 71395 that has a radial velocity trend suggesting a massive planet in large orbit. The chosen observation wavelength is very well suited for very high contrast imaging of close companions at this age and makes this survey unique. The goal was to detect substellar companions to these stars at distances as close as 5-20 AU and ultimately to detect giant extrasolar planets down to a few Jupiter masses, to measure their frequency, and - by comparison with models - determine their physical properties. This paper presents the results obtained on a subsample of 12 stars that have been observed during ESO P73.

The influence of non-isothermal atmosphere on the intensity of details of Raman Scattering is computed for spectra of Uranus and Neptune. It follows that the intensity of this scattering depends on the depth of the level formation in an optically homogeneous non-isothermal atmosphere; neglecting of real temperature profiles during the analysis of observation data leads to large errors in the parameters of the atmosphere upper level.

We compute theoretical infrared light curves for several known extrasolar planets. We have constructed a set of routines to calculate the orbital parameters for a given planet and integrate over the planetary disk to determine the total flux density of the planet as it orbits the parent star. We have further developed a spectral synthesis routine to calculate theoretical spectra of extrasolar giant planets from 3–24 $\mu$m. The code requires a temperature-pressure profile as input, calculated by solving the radiative transfer equation; it then calculates continuous opacities and line opacities for water, carbon monoxide, and methane, and finally integrates over the layers of the atmosphere to determine the emergent flux. By integrating the theoretical spectrum over the bandpass of a particular instrument and including realistic instrument noise, we produce a set of multi-wavelength, infrared light curves. Using these light curves, we predict whether a particular known planet can be observed and characterized using the Spitzer Space Telescope, as well as other proposed space-based instruments, such as the Fourier-Kelvin Stellar Interferometer (FKSI) and the James Webb Space Telescope (JWST).

We present ground-based disc resolved polarimetric imaging and spectropolarimetry of Uranus and Neptune in the wavelength range from 530 to 930 nm with the goal to constrain the expected polarization of extra-solar planets with similar atmospheric properties. We find for both planets a high limb polarization as expected for atmospheres with significant Rayleigh scattering layers. The limb polarization is enhanced in the strong methane absorption bands when compared to the adjacent continuum. From the observed polarization features we conclude that extra-solar planets with atmospheric properties similar to Uranus and Neptune are strongly polarized and well suited for polarimetric detection and investigation.

The Automated Patrol Telescope, operated by the University of New South Wales, has been undertaking a search for extrasolar planets using the transit method. We present lightcurves from two recent promising candidates; spectroscopic follow-up using the ANU 2.3m telescope shows that the companions are probably low mass stars rather than planets, although more data will be needed to be certain. Additionally, we outline future improvements to our transit search: a hardware upgrade scheduled for 2006, and the addition of a robust trend-filtering algorithm to the data reduction software.

This paper describes a novel concept for the direct detection of exoplanets involving two spacecraft. One spacecraft is an occulter, designed to provide adequate starlight suppression within its shadow. The second spacecraft, a conventional telescope of standard quality, is flown into the shadow of the first and used to collect the light from the target planet. The design of the occulter and its expected performance are discussed. It is shown that is possible to simultaneously achieve the necessary contrast ratios and inner working angles necessary to have a scientifically meaningful mission. A brief discussion of the estimated tolerances indicate that such a mission is feasible in the near term.

ELT's, interferometers and their multi-aperture direct-imaging form called hypertelescopes are expected to provide images of exo-Earths, and even resolved images in the latter case. Both terrestrial and space versions are potentially usable, although high-performance adaptive optics will be needed on Earth. Current advances in the way of hypertelescopes on Earth and in space are briefly described.

Direct detection of a planet around a star by a nulling interferometer, requires to minimize as far as possible the stellar leaks due to the resolved angular size of the star. The original Bracewell configuration features a nulling function in $\theta^{2}$ which is insufficient in many cases. Several interferometric configurations have been proposed in order to improve the quality of the rejection with a nulling function $\theta^{n}$ with $2 \leq n \leq 6$. I proposed recently a method to build linear configurations of telescopes that achieve nulling function $\theta^{n}$ for any even value of n, using the Prouhet-Thué-Morse sequence to select those telescopes where a π phase shift is applied. In a first part, I recall the basis of this method and its generalization to 2D configurations and 1D arrays of non-identical telescopes, or even to configurations where the phase shift is not π. In a next step, I evaluate the efficiency of deep nulling interferometers in real world, i.e. when nulling is not perfect because of variations of distances or of phase shift between telescopes. I conclude that there is a clear advantage given by the highest order systems that keep a better nulling capability than conventional interferometers, even in severe conditions where parameters driving the nulling performance are highly fluctuating.

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a spacecraft-borne imaging and nulling interferometer for the near to mid-infrared spectral region. FKSI is a scientific and technological pathfinder to the Darwin and Terrestrial Planet Finder (TPF) missions and will be a high angular resolution system complementary to the James Webb Space Telescope (JWST). There are four key scientific issues the FKSI mission is designed to address. These are: 1.) characterization of the atmospheres of the known extra-solar giant planets, 2.) assay of the morphology of debris disks to look for resonant structures characteristic of the presence of extrasolar planets, 3.) study of circumstellar material around a variety of stellar types to better understand their evolutionary state, and in the case of young stellar systems, their planet forming potential, and 4.) measurement of detailed structures inside active galactic nuclei. We report results of simulation studies of the imaging capabilities of the FKSI, current progress on our nulling testbed, results from control system and residual jitter analysis, and selection of hollow waveguide fibers for wavefront cleanup.

The Keck Interferometer Nuller (KIN) is one of the major scientific and technical precursors to the Terrestrial Planet Finder Interferometer (TPF-I) mission. KIN's primary objective is to measure the level of exo-zodiacal mid-infrared emission around nearby main sequence stars, which requires deep broad-band nulling of astronomical sources of a few Janskys at 10 microns. A number of new capabilitites are needed in order to reach that goal with the Keck telescopes: mid-infrared coherent recombination, interferometric operation in “split pupil” mode, N-band optical path stabilization using K-band fringe tracking and internal metrology, and eventually, active atmospheric dispersion correction. We report here on the progress made implementing these new functionalities, and discuss the initial levels of extinction achieved on the sky.

The European Space Agency's Darwin and NASA's Terrestrial Planet Finder (TPF) are among the most challenging space science missions ever considered. Their principal objective is to detect Earth-like planets around nearby stars and to characterize their atmospheres. Darwin and TPF-I are currently conceived as nulling interferometers with free-flying telescopes. Within the frame of the Darwin program, the ESA and the European Southern Observatory (ESO), supported by European industries and scientific institutes, have performed two parallel Phase A studies of a ground-based nulling interferometry experiment (GENIE) at the site of ESO's Very Large Telescope Interferometer (VLTI) in Paranal, Chile. GENIE will demonstrate several key technologies required for the Darwin mission. Its science objectives include the detection and characterization of dust disks and low-mass companions around nearby stars. These studies have established detailed instrumental designs, in which GENIE will operate in the L' band around 3.8 microns as a single Bracewell nulling or constructive interferometer, using either two Auxiliary or two Unit Telescopes. The studies were supported by detailed numerical simulations which indicated the possibility of detection and low-resolution spectroscopy in nulling mode of extra-solar giant planets (EGPs) with atmospheric temperatures down to 700 K, provided that a proper calibration of instrumental effects is applied. Detection of circumstellar exo-zodiacal (EZ) dust clouds is possible down to 0.5 mJy, with interesting prospects for the characterization of planet-forming disks.

The space mission PEGASE, proposed to the CNES (Centre National d'Etudes Spatiales = French Space Agency) in the framework of its call for scientific proposals : “formation flying missions”, is a 2-aperture interferometer, composed by 3 free flying satellites (2 siderostats and 1 beam combiner), allowing baselines from 50 to 500 m in both nulling and visibility modes. With an angular resolution of a few mas and a spectral resolution of several tens in the spectral range 2.5-5 microns, PEGASE has several goals:

1. science : spectroscopy of hot jupiters (Pegasides) and brown dwarves, exploration of the inner part of protoplanetary disks

2. technology : validation in real space conditions of formation flying, nulling and visibility interferometry concepts.

The search for extraterrestrial technology effectively began 45 years ago with Frank Drake's Project Ozma and a radioastronomy start to the search for extraterrestrial intelligence (SETI). Eventually searches began for possible interstellar probes in stable orbits in the Solar System, as well as for infrared excesses from possible Dyson spheres round Sun-like stars. Whilst the Cold War was still underway, some scientists looked for evidence of nuclear waste dumps and nuclear wars elsewhere in the Milky Way. None of this work was carried out by archaeologists, even though by their very nature archaeologists are experts in the detection of ancient technologies. The technologies being searched for would have been partly ancient in age though advanced in techniques and science. The development of ESA's Darwin and NASA's TPF for detection and imaging of Earth-like exoplanets in our galactic neighbourhood represents an opportunity for the testing of techniques for detecting signatures of technological activities. Ideally, both Darwin and TPF might be able to provide spectroscopic data on the chemistry and biochemistry of the atmospheres of Earth-like exoplanets, and thus to detect some of the signs of life. If this can be accomplished successfully, then in theory evidence for pollution and nuclear accidents and wars should be detectable. Some infrared signatures of ETT on or round exoplanets might be detectable. Direct visual imaging of ETT structures will probably not be feasible till we have extremely powerful interstellar telescopes or actually send orbital craft.