Abstract
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) was proposed in 2010 for a a five-year M-class mission in the context of ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets located at several AUs (0.5-10 AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses down to Super-Earths (∼2 Earth radii, ∼10M⊕), possibly habitable. In addition, circumstellar disks as faint as a few times the zodiacal light in the Solar System can be studied. SPICES is based on a 1.5-m off-axis telescope and can perform spectro- polarimetric measurements in the visible (450-900 nm) at a spectral resolution of about 40. This paper summarizes the top science program and the choices made to conceive the instrument. The performance is illustrated for a few emblematic cases. 1. SCIENCE PROGRAM SPICES is an evolution of the former SEE-COAST proposal (11) and belongs to the category of so-called small coronagraphic telescopes derived from the Terrestrial Planet Finder concept (8). It is a direct imaging mission designed to achieve very high contrasts in order to characterize exoplanetary systems previously identified by other instruments/techniques (radial velocity, astrometry, direct imaging). This challenging goal clearly requires a specific instrumentation, which is not available on any other present or future facility and must be optimized for a very specific task. Typical star/planet brightness ratios in reflected light are in the range of 10 8 to 10 10 at less than 1 arcsec. SPICES combines several techniques for high contrast imaging in a single instrument designed to maximize the astrophysical return while reducing risks. A more precise description of the proposal can be found in (3) while detailed simulations are presented in (9). We here extract a few important results from these two reference papers. The primary objective of SPICES is to characterize the atmospheres and possibly surfaces of various types of planets: gaseous and iced giants as well as Super-Earths. For that purpose, SPICES combines direct imaging with spectro-polarimetry in the visible (450-900nm) and measures the total flux F and the linearly polarized fluxes Q and U, all as functions of the wavelength , for every pixel in an image.
Highlights
SPICES is based on a 1.5-m off-axis telescope and can perform spectropolarimetric measurements in the visible (450–900 nm) at a spectral resolution of about 40
SPICES is an evolution of the former SEE-COAST proposal [11] and belongs to the category of so-called small coronagraphic telescopes derived from the Terrestrial Planet Finder concept [8]
It is a direct imaging mission designed to achieve very high contrasts in order to characterize exoplanetary systems previously identified by other instruments/techniques
Summary
SPICES is an evolution of the former SEE-COAST proposal [11] and belongs to the category of so-called small coronagraphic telescopes derived from the Terrestrial Planet Finder concept [8] It is a direct imaging mission designed to achieve very high contrasts in order to characterize exoplanetary systems previously identified by other instruments/techniques (radial velocity, astrometry, direct imaging). Giant planets (both gaseous and icy) are definitely the main targets for SPICES since they will reflect more light than the emblematic but smaller Super-Earths, so that a high level of atmospheric characterization can be achieved through both spectroscopy and polarimetry. The geometric albedos of Uranus and Neptune are much lower but clearly show Rayleigh scattering at the shortest wavelengths, because for these colder planets, most of the cloud layers are located deeper in the atmosphere, which contains significantly more methane gas. The water and ammonia clouds that will likely be found in the atmospheres of planets in SPICES detection range will indicate atmospheric temperature and composition [4]
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