High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)

Abstract

A complete census of planetary systems around a volume-limited sample of solar-type stars (FGK dwarfs) in the Solar neighborhood (d ≤ 15 pc) with uniform sensitivity down to Earth-mass planets within their Habitable Zones out to several AUs would be a major milestone in extrasolar planets astrophysics. This fundamental goal can be achieved with a mission concept such as NEAT -the Nearby Earth Astrometric Telescope.NEAT is designed to carry out space-borne extremelyhigh-precision astrometric measurements at the 0.05 µas (1σ) accuracy level, sufficient to detect dynamical effects due to orbiting planets of mass even lower than Earth's around the nearest stars. Such a survey mission would provide the actual planetary masses and the full orbital geometry for all the components of the detected planetary systems down to the Earth-mass limit. The NEAT performance limits can be achieved by carrying out differential astrometry between the targets and a set of suitable reference stars in the field. The NEAT instrument design consists of an off-axis parabola singlemirror telescope (D = 1m), a detector with a largeThe complete affiliations are given at the end of the paper. The full list of members of the NEAT proposal is avialable at http://neat.obs.ujf-grenoble.fr.field of view located 40 m away from the telescope and made of 8 small movable CCDs located around a fixed central CCD, and an interferometric calibration system monitoring dynamical Young's fringes originating from metrology fibers located at the primary mirror. The mission profile is driven by the fact that the two main modules of the payload, the telescope and the focal plane, must be located 40 m away leading to the choice of a formation flying option as the reference mission, and of a deployable boom option as an alternative choice. The proposed mission architecture relies on the use of two satellites, of about 700 kg each, operating at L2 for 5 years, flying in formation and offering a capability of more than 20,000 reconfigurations. The two satellites will be launched in a stacked configuration using a Soyuz ST launch vehicle.The NEAT primary science program will encompass an astrometric survey of our 200 closest F-, Gand K-type stellar neighbors, with an average of 50 visits each distributed over the nominal mission duration. The main survey operation will use approximately 70% of the mission lifetime. The remaining 30% of NEAT observing time might be allocated, for example, to improve the characterization of the architecture of selected planetary systems around nearby targets of specific interest (low-mass stars, young stars, etc.) discovered by Gaia, ground-based high-precision radial-velocity surveys, and other programs. With its exquisite, surgical astrometric precision, NEAT holds the promise to provide the first thorough census for Earth-mass planets around stars in the immediate vicinity of our Sun.

The Short-term Stability of a Simulated Differential Astrometric Reference Frame in theGaiaEra

“…For systems for which a robust set of references can be established, such methodology could be particularly effective for the confirmation of astrometric signals corresponding to peculiar cases, such as edge-on, faceon, and highly eccentric orbits, and it might also help in the interpretation of Gaia data for very bright stars. The establishment of a robust framework for the proper modeling of narrow-field astrometry at the µas level will also be valuable in the perspective of future efforts to exploit the technique for detection of orbital motion induced by terrestrial planets in the Habitable Zone of the nearest solar-type stars (Malbet et al 2012). …”

Line-of-sight based formation keeping and attitude control of two spacecraft

“…The Euler's equations of motion for the ith (i¼1,2) spacecraft's attitude in SO(3) ( [18], Section 3.3), are is the map such that ( ) = × x y x y S for any ∈  x y , 3 . We use the double integrator model for the translation dynamics of the center of mass of each spacecraft, which for the ith spacecraft can be written as, ([19], chapter 12)…”

“…In recent years, there have been several proposals (for example Simbol-X [1], MAXIM [2], and NEAT [3]) for spacecraft formation flying missions with multiple spacecraft in cooperation to function as a powerful virtual instrument. Compared to a monolithic spacecraft, these formation flying missions promise to be more robust and flexible.…”

Phase-Referenced Interferometry and Narrow-Angle Astrometry With Susi

“…Using a sophisticated algorithm to measure the position of an image of a star to an accuracy of one-millionth of a pixel, this technique could achieve astrometric precision of 10µas or better (Casertano et al, 2008;Malbet et al, 2012;Sozzetti, 2011). GAIA is an instrument designed to do just this.…”