By 2020, ground- and space-based facilities will have discovered thousands of massive (Neptune- and Jupiter-mass) exoplanets. ... The next step in exoplanet research will be the physical characterisation of the then known planets.
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| Left: The most massive globular cluster in the Milky Way: Omega Centauri, ~ 30 light-years across, potential host of a 10 000 solar-mass black hole to be confirmed with the E-ELT. Right: Simulated mid-infrared image of a massive young star cluster at the distance of the Galactic Centre. The cluster is heavily obscured and reddened by dust, causing up to 200 magnitudes of extinction in the visual. The E-ELT will be able to resolve stars in deeply dust-extincted regions and in other stellar systems out to distances of 55 million light-years. Credit: The E-ELT Project office / ESO |
In order to achieve this, direct light from the planet must be detected and separated from the glare of its parent star. Overcoming this difference in brightness (usually referred to as the contrast) is the main challenge for this type of observation and requires extremely sharp imaging. This capability will be a huge strength of ground-based telescopes. Planet-finder instruments on 8-metre-class telescopes will achieve similar contrasts to the
JWST: around 10
–5 to 10
–6 at sub-arcsecond distances from the parent stars. The detection of an Earth twin requires contrast of 10
–9 or better at about 0.1 arcseconds from the star (for the tens of stars within 30 light-years from the Sun). The unprecedented light-gathering power of a 40-metre-class telescope, and the implementation of extreme adaptive optics at the E-ELT are absolutely crucial for reaching this limit. A planet-finder instrument on the E-ELT will allow scientists not only to study young (self-luminous) and mature giant planets in the Solar Neighbourhood and out to the closest star-forming regions but also to understand the composition and structure of their atmospheres. Around the nearest hundred stars, the E-ELT will enable the first characterisation of Neptune-like and rocky planets located in habitable zones, establishing a new frontier in astrobiology and in our understanding of the evolution of life.
With the E-ELT, the detailed study of the atmospheres of young, massive exoplanets becomes feasible. Indeed, with its unprecedented sensitivity and high spatial resolution at near- and mid-infrared wavelengths, the E-ELT will be able to detect young, self-luminous exoplanets of Jupiter mass. The contrast between star and planet at these wavelengths becomes so advantageous that, for the nearest stars, hydrogen, helium, methane, water ammonia and other molecules can all be detected in low-resolution spectra of the atmospheres of super-Earth planets in habitable zones.
Alternatively, exoplanet atmospheres can be observed during transits in the optical and near-infrared. Ground- and space-based facilities (such as the
CoRoT and
Kepler missions) are accumulating target stars for which an exoplanet, as seen from Earth, transits in front of its parent star. During these events, which last a few hours every few months or years, spectral features of the exoplanet’s atmosphere, back-lit by their parent star, can be seen in the spectrum of the system. Such measurements are barely feasible at present from the ground and space, but lie well within reach of the E-ELT, which will be able to sample several important chemical diagnostic lines.
In the case of rocky planets in the habitable zone, the spectra can be examined for the biomarker mole- cules that are indicative of biological processes, offering perhaps the best opportunity to make the first detection of extraterrestrial life.
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| This simulated (1 arcsecond × 1 arcsecond) near-infrared image of a field near the centre of Messier 87, the giant galaxy at the core of the Virgo galaxy cluster, demonstrates that the E-ELT will be able to resolve individual stars even in the dense inner regions of giant elliptical galaxies 55 million light-years away, surpassing the capabilities of the JWST. Credit: The E-ELT Project office / ESO |
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| Illustration of the gain in spatial resolution when observing a galaxy at z = 2 (10 billion years lookback time) with the E-ELT. The E-ELT will be able to resolve such high redshift galaxies and measure structural parameters and scaling relations. Credit: The E-ELT Project office / ESO |
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| Simulation of the direct imaging of exoplanets with the E-ELT. Upper left: Single, one-minute raw exposure at 0.9 µm of a star at a distance of 10 parsec (pc) hosting seven planets (with a contrast of 10-6–10-7), equivalent to up to 10-9 in a 10-hour exposure. Upper right: After processing using spectral deconvolution, all seven planets are now clearly visible. Bottom: Simulation of the direct imaging of exoplanets exploring the effects of different coronagraphs — the chromaticity of the coronagraphs is the current limiting factor at small radii. Credit: The E-ELT Project office / ESO |
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