THE E-ELT DESIGN REFERENCE MISSION - SCIENCE CASE S3
Direct imaging of terrestrial and giant exoplanets
We propose to perform a direct imaging search in the J-band (1.2 μm) for terrestrial and giant planets around 150 FGK stars within 20 pc from the Sun. Using the 42m-ELT equipped with a high-contrast coronagraph and simultaneous differential imaging we intend to achieve a contrast of 1 × 10-10 beyond an angular distance of 8 λ/D (> 50 mas) from each parent star. The observations will be conducted to ensure detection (S/N=5) of the reflected light from Earth-like planets in the habitable zone of the parent stars (i.e. at ~ 1 AU orbital distance of the solar-type stars in the sample). This will allow a rather extensive demographic study of terrestrial and giant exoplanets over a wide range of separations leading to a better understanding of the formation mechanism of planetary systems. Second and third epoch observations will be required to determine orbital motion. Follow-up low-resolution spectroscopy (R=100) in the near IR will be pursued for the nearest detected exoplanets.
Predictions for EPICS, R. Gratton at
SWG meeting, 07 Oct 2008
Simulations, C. Vérinaud at DRM workshop, 20-21 May 2008
EPICS, R. Gratton at SWG meeting, 02 Apr 2008
Simulations, R. Gratton at SWG DRM workshop, 29-30 May 2007
Overview (#1 in a series of popular science level 'pep talks'), J. Liske at TPO meeting, 21 Nov 2007
Earth twins in the habitable zone of solar-type stars
Five years of sub-m/s radial-velocity measurements of quiet stars in the HARPS-GTO planet-search programme have unveiled the tip of a large population of Neptune-mass and super-Earth planets present around 30% of G and K dwarfs of the solar neighborhood, within 0.3 AU from the central star. These findings support recent results of synthetic planet-population models that also predict the existence of a large population of Earth-mass planets at all separations. We propose in this ambitious large program to directly probe the presence of Earth twins in the habitable zone in a sample of 20 close-by solar-type stars, through radial velocities obtained with the high-resolution optical spectrograph CODEX on the European Extremely Large Telescope (hereafter E-ELT). The high resolution and long term stability of CODEX coupled with the large collecting area of the E-ELT provide an unequaled facility for measuring stellar radial velocities at the few cm/s level. Simulations show that stellar noise (p-mode, granulation, activity) can be averaged down to this level for the quietest dwarf stars. The scientific goals of the proposal are 1) to detect Earth-mass planets in the habitable zone around solar-type stars and thus build-up a list of suitable targets for future space missions aiming at characterizing their atmosphere; 2) to determine the frequency of Earth twins around neighboring stars; 3) to derive statistical properties of low-mass planets, priceless constraints for planet-formation models; and 4) to characterize the multi-planet aspect of systems with Earth twins.
Rocky planets in the habitable zones of low-mass stars and brown dwarfs
M.R. Zapatero Osario
Our current knowledge of exo-planetary systems is biased toward solar-type stars and giant planets with masses similar to those of Jupiter and Saturn. Very little is known regarding the population of smaller planets, and the frequency and distribution of planets orbiting low-mass stars and brown dwarfs. From current radial velocity searches, there is evidence for low-mass stars having less massive planets than solar-type stars. In addition, theory predicts that the protoplanetary disks around low-mass stars and brown dwarfs can lead to the creation of small planets rather than giant planets. The findings of planets of different masses (from Earth sizes up to Jovian planets) around a wide variety of stars and brown dwarfs is critical to understand the evolution of circum(sub)stellar disks and the formation of planetary systems, including our own.
The search for telluric planets around low-mass stars and brown dwarfs via the Doppler technique is advantageous since, for a given orbital size, the amplitude of the central object motion around the center of mass of the system is larger than in the case of the solar-type stars. Furthermore, the detection of exo-Earths around low-mass stars and brown dwarfs using the radial velocity method is "easier" than around more massive stars in terms of velocity accuracy. An exo-Earth at a separation of 0.2 AU (i.e., within the expected habitable zone) from a 0.2-Msolar star will impose a velocity amplitude of 45 cm/s into its parent star, while our Sun is moving with an amplitude of 9 cm/s because of the Earth. Earth-like planets orbiting a 50-MJup brown dwarf should be effortless to pick: amplitudes of 180 and 58 cm/s at orbits of 0.05 and 0.5 AU, respectively, are expected. A radial velocity survey of all known M, L and T dwarfs within 10 pc of the Sun with an accuracy of 10 cm/s or better could reveal Earth-like and even smaller planets providing crucial insight on frequency and formation process of these objects.
Physical properties of Earth-sized planets
Photometric space missions (like CoRoT or Kepler) will provide small-size transit candidates for stars as faint as V=14-15, among them a certain number of Earth-size planets (and below). For short-period planets (< ~15 days) of masses similar to the Earth, we expect a reflex motion corresponding to a radial-velocity variation of ~20 cm/s. The needed precision to confirm the planetary nature of the transiting body will be easily achieved with CODEX on the ELT. The potential activity-related jitter will not be a strong perturbation as the orbital period and phase will be known from the photometric measurements. Simulations show that that the mass of an Earth-mass planet on a 4-day period can be constrained at the 10% confidence level with ~25 measures at a precision of ~20 cm/s. This makes the cost in telescope time at the level of about 2 nights per candidate. These measurements combined with the photometric transit results will provide the radius, mass and mean density of Earth-size planets (rocky, icy?) on short-period orbits. They will provide information on the diversity of structure of these objects potentially formed in different locations of the system, and bring unprecedented constraints for the models of planet inner structure.
Project Science Team
Phase B (2006 – 2011)