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The Solar System at ~10 mas perspectives for a Fresnel imager

The Solar System at ~10 mas perspectives for a Fresnel imager. Paolo Tanga Marco Delbò Laboratoire Cassiopée, OCA. Observational challenges. Hi-res atmospheric activity & aurorae (UV) on Jupiter, Saturn Atmospheric activity on the remote planets

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The Solar System at ~10 mas perspectives for a Fresnel imager

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  1. The Solar System at ~10 mas perspectives for a Fresnel imager Paolo Tanga Marco Delbò Laboratoire Cassiopée, OCA

  2. Observational challenges • Hi-res atmospheric activity & aurorae (UV) on Jupiter, Saturn • Atmospheric activity on the remote planets • Evolution of fine structures in Saturn’s rings • … • Trans-Neptunian Object population: • Inventory • Size (albedo) • Anomalous orbits • Asteroids: • Inventory at small sizes • Internal structure (mass, size, shape) • Cometary activity • Comets • Evolution of chemicals after sublimation

  3. Giant planets • UV features: • Aurorae • Upper atmospheric features (40-100 mb) • Interest • Connection to magnetosphere • Coupling to other wavelengths • Our nearby prototype of extrasolar planets! HST, H2 emission (160 nm)

  4. The importance of asteroids… The great issues:  Origin: collisional life, related physics  Dynamical processes: transport, mixing in the primitive nebula, origin of meteorites  Impact risks and mitigation strategy The problem… Very limited knowledge of basic properties: • density, porosity… • Spectral types and connection to composition • Shapes, satellites • Size distribution

  5. Itokawa as seen by Hayabusa 540 m Is this a cohesionless « gravitational aggregate »?

  6. How much is/will be known Property today after Gaia shapes, poles 100 ~100,000 rotation periods 1000 10,000 satellites ~ 20 (MBA) ? New constraints! surface properties ~ 1000 ~200,000 astrometry ~ 0"5 0"005 masses, s < 50% ~ 50 150 size / albedos ~2000 3000

  7. Ceres ~200 asteroids 1 x 106 (?) 1 x 106(?) Jupiter Neptune Mars Angular size as a function of distance for objects of 10 and 100 km. The two « p » curves represent the limit size at V=20 (at opposition) for two extreme albedo values.

  8. Areas open to a Fresnel imager • Size inventory/improvement 10-100 km • Macroscopic shapes 10-100 km • Cometary activity (OH at 308 nm) • Binary asteroids • Discovery • Orbits

  9. Binary asteroids • Importance: • Linked to the collisional physics  past history of the belt • Period + separation  mass • If size is known  density (internal properties) • Properties: • Wide range of separations and size ratios! • 16% of objects at D<30 km?

  10. Binary asteroids – the Fresnel imager domain Imaging (AO) radar/ lightcurves

  11. How many asteroids at V=20 ? • Evolution of the number of entries H < Hlim • old files retrieved by D. Hestroffer in the IMCCE archives

  12. Sun 45° L2 Geometric observability of orbits

  13. Velocity distribution • simulation on 5,000 objects • main-belt, NEOs  Possible problems related to motion s ~ 12 mas/s

  14. Possible strategies: • Priority given to Solar System objects • Exceptional events (comets, storms on the main planets…) • Specific long-term monitoring programs • « Opportunity » targets • ~50 asteroids V<20 in 1 sq. degree • Few requirements on pointing

  15. Conclusions • Asteroids offer a wide variety of targets • Binary objects • Cometary activity • Giant planets • Interesting features at all wavelengths • Can help in modeling extrasolar planet observations

  16. Configuration space period-diameter • no very fast rotator due to centrifugal force • lack of global cohesion

  17. The occultation revival • Today • poor predictability for objects <50 km • bright Hipparcos/Tycho stars favoured • ~0.1 events/objects/year • Current practical limit: 100 km at 10% accuracy • After Gaia (100 X orbit improvement): • Uncertainty smaller than the asteroid at >20 km • 1-m automated telescope(s): • Single site: 20-40 events/yr for an object • of ~20 km • Network: completeness of diameters • > 20 km in a few yr • Projected shape known

  18. Animation: M. Delbo Light curves • Asteroid’s magnitude function of: • shape, rotation period, direction of spin axis • Direct problem: • model of light curves for different shapes and rotation • Inverse problem: • find the rotation parameters from photometric data • strongly non linear • not well conditioned if period unknown

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