ASTEROID PHYSICAL PROPERTIES FROM ASTROMETRY

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Malediction

• del Inca?
• de Uranus?
• What's next?

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Outline

• Asteroid mass
• Binaries - Statistical orbit determination
• Close encounter - Gaia mission
• Physical properties
• an HRA excursion

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Asteroid mass for/from

• Planetary ephemerides
• Inner planets accuracy limited by bad knowledge
  of asteroid perturbations
• Physical properties
• fundamental parameter bulk density,
  differentiation, link with taxonomy - surface
  spectroscopy meteorit analogues, solar system
  formation
• From binaries or close encounter (aster/planet
  aster/probe aster/aster)

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Binary asteroids multiple systems

• Do asteroids have satellites?
• S. Weidenschilling et al. (Asteroids II)
• Asteroids do have satellites
• W. Merline et al. (Asteroids III)
• Even more than one

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Orbit determinationfrom Statistical Inversion

• Unknown orbit few points, sparse data
• True Keplerian orbit
• visual / resolved or astrometric
• stellar or solar system objects
• mass from 3rd Kepler law (a, P)
• Star no parallax gt symmetric solution
• SSO parallax gt 1 solution (possible)
• Analytical (Thiele-Innes) 1D Monte-Carlo

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Binary star
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Binary star

• p.d.f., MLE
• Bayesian, a priori knowledge
• orbital evolution
• stability regions for planetary systems

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Low mass companion to stars
court. S. Pravdo (JPL) 2004 ApJ 617
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court. W. Grundy (Lowell obs.)
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Main Belt Aster - Trojan

• LAOSA (F. Marchis) data base of AO obs

87 Sylvia, VLT
617 Patroclus, KeckLGS
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TNOs (1999 RZ253)
K. Noll et al., HST/HRC obs. Icarus 2004
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Binary asteroids multiple systems

• Most direct and accurate method to have mass
• Not all known systems have (good) mass
  determination yet
• Not all systems have complete orbit

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Scanning telescope

• Spin P6h
• Precession 63d
• 2 FOVs
• 1 sky coverage 6month

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Payload
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Focal plane
Astrometric Field
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3D census of our Galaxy
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3D census of our Galaxy
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300,000 asteroids
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Obs. distribution

• Time .......... asteroid Piazzia

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Obs. distribution

• Space, orbit

Can be different for NEAs, Centaurs,...
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Orbit improvement

• Sigma 0.3 -- 5 milli-arcsec

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Orbit improvement

• Non gravitational effect
• Tests of GR (PPN ?, dot G, ...)
• Reference frames
• Mass of asteroids (S. Mouret Ph.D.)

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Close encounter (S. Mouret)

• gravitational pull
• selection impulse approach
• mass full num. integration

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Gaia masses
Dawn
Currently unknown
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Gaia masses

• 150 asteroids with precision lt 50
• Reduced simulations gt more targets
• Compl. ground-based observations

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Physical Properties

• Mass, bias
• encounter mainly MBA massive
• binary mainly MBA, TNOs formation
• Bulk density, volume
• Asteroid interior, meteorit analogues
• Figures of equilibrium
• ?? f(?,shape) compres.

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Porosity
real?
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Figures of equilibrium
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An HRA excursion

• Modulated Photometry

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Modulated photometry

• Carlsberg and Bordeaux meridian, Multi-channel
  Astrometric Photometer

astrometry
instrument

• Multiple or extended source add linearly

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Modulated photometry ---------------

• Extended object symmetry II(r)Io ???????

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Modulated photometry Intensity interferometer

• Extended object symmetry II(r)Io ???????

x ? 2? B / ?
Visibility for uniform disk
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Modulation/Visibility
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