GAIA: SOLAR SYSTEM ASTROMETRY IN DR2 P. Tanga 1, F. Spoto1,2 1Observatoire de la Côte d’Azur, Nice, France 2IMCCE, Observatoire de Paris, France P. Tanga – Gaia and the Solar System 2 Gaia is observing asteroids - Scanning the sky since July 2014 (operational phase) - Solar elongations 45° to 135° - Limiting magnitude V~20.5 - 100.000 asteroid observations (CCD level) / day 45° Sun IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 3 Gaia DR2 - Solar System On the base of a pre-seleCted list of known objeCts > 10 FOV transits over the 22 months of DR2 August 5, 2014 - May 23, 2016 Objects 14 099 Epoch astrometry 1 997 702 CCD positions 287 904 transits (52% : photometry) Typ. accuracy <1 mas (along scan) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 4 Gaia DR2 - Solar System statistiCs 1:0e5 1200 8e4 1000 6e4 800 600 4e4 400 2e4 200 0 0 10 11 12 13 14 15 16 17 18 19 20 0 100 200 300 400 500 600 Number of observations per object G mag 1000 100 10 1 1 2 5 10 20 50 a (AU) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 5 Gaia DR2 - Solar System - single transit astrometriC performanCe Residuals from the orbital fit of Gaia DR2 data only (along-scan direction) Spoto et al. 2018 IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 6 Asteroid (386) Siegena - residuals from orbital fit Combining arChive data (2776 obs.) to GDR2 0:4 0:03 4 0:3 0:02 0:2 2 ) ) ) 0:01 s s s a 0:1 a a ( ( ( l l l a a a u 0 u u 0 d d 0 d i i i s s s e e e r r r c c c ¡ : e e 0 01 e ¡0:1 D D D ¡2 ¡0:2 ¡0:02 ¡4 ¡0:3 ¡0:03 ¡0:4 ¡4 ¡2 0 2 4 ¡0:4 ¡0:3 ¡0:2 ¡0:1 0 0:1 0:2 0:3 0:4 ¡0:02 0 0:02 RA residual (as) RA residual (as) RA residual (as) factor 100 X improvement! IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 7 The situation, before Gaia • 1.9 x 108 measurements in the arChives of the Minor Planet Center • mostly CCD imaging • average acCuracy: 0.4 as • ~2000 radar ranging measurements • equivalent acCuracy : 10-50 mag IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 8 Some Challenges for asteroid astrometry Discover asteroid satellites New / precise asteroid masses from their wobbling 0.5 - 10 mas 1000s encounters/year > 10 mas Improve predictions of stellar occultations ~a few mas Measure the orbital drift due to Yarkovsky force IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 9 Yarkovsky effeCt: why we Care • Yarkovsky appliCations: – NEO and meteorite transport – physiCal properties (spin, density…) – family dispersion, ages Spoto et al. 2015 • The Challenge: measure a few, apply to many —> ConneCtion to speCtro- photometry by Gaia: • low-res speCtra: taxonomy in the visible • mmag photometry: shape determinations • Large sample by end of mission: ~ 350 000 Delbo, Galluccio, De Angeli, ESA/Gaia/DPAC IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 10 Yarkovsky and Gaia ? ~ 3 x 10-9 AU Pre-Gaia orbit quality (MPC data) 1/D (1/km) In DR2: – 3 NEOs with measured Yarkovsky – 5 NEOs with marginal deteCtion – about 20 good MB Candidates Orbit uncertainty (km) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 11 Asteroid family members in DR2 4676 family members in DR2 (from AstDys membership) 0:6 0:5 0:4 ) i ( n : i 0 3 s 0:2 0:1 0 1:6 1:8 2:0 2:2 2:4 2:6 2:8 3:0 3:2 3:4 3:6 3:8 4:0 a (AU) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 12 Joint exploitation Gaia + pre-Gaia astrometry: bias example Asteroid (1132) Hollandia Liverpool TelesCope + VST (8 hours apart) & MPC ground-based data (~1900 positions) 0.2 0.2 PPMXL calibration Gaia calibration 0.1 VST 0.1 LT+VST 0 0 -0.1 -0.1 O-C Dec (as) O-C Dec (as) LT -0.2 -0.2 -0.4 -0.3 -0.2 -0.1 0 0.1 -0.4 -0.3 -0.2 -0.1 0 0.1 O-C RA (as) O-C RA (as) (credits: Gaia GBOT team) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 13 The occultation astrometry with Gaia • DR2 already suCCessfully exploited • Triton (OCtobre 3, 2017) • 2014 MU69 (V=27.5, 50 km KBO, ~1.4 mas)!! 1e 4 15 ¡ • OCCultations: very acCurate asteroid 14 ) 13 u 1e 5 a position at the level of the star ¡ s ( 12 n a o ¾ 11 i 1e 6 t astrometry s a n ¡ 10 t l o i u t 9 c a • 1e 7 c …Beyond the duration of Gaia! t l ¡ 8 o u c 7 N c 1e 8 O ¡ equal accuracy 6 5 1e 9 4 ¡1e 9 2e 9 5e 9 1e 8 2e 8 ¡ ¡ ¡ ¡ ¡ All observations ¾a(au) IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 14 RobotiC observations of asteroid oCCultations • Extension to faint magnitudes and small asteroids • Only method providing ~Gaia acCuracy • 50 Cm robotiC telesCope at OCA, FranCe ASTROMETRIC OBSERVATIONS DATA EXPLOITATION: YARKOVSKY, IMPROVED OCCULTATION DYNAMICAL MODEL PREDICTIONS AND ORBITS IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 15 Conclusions • Gaia DR2 asteroid data: the first sample, already useful to test subtle dynamiCal effeCts • Yarkovsky determination • general orbit improvement • appliCation to stellar oCCultations • Combination with other observations: it starts to work… • but weighting of the data is CritiCal • acCurate debiasing is required • a new method suCCessfully implemented and tested • Yarkovsky deteCtion in the Main Belt is getting Closer… IAU 30 GA - Wien - 2018 P. Tanga – Gaia and the Solar System 16 Diffusion of asteroid alertsFrom the Gaia-FUN-SSO web site (the red contours are computed by the SSO-ST pipeline and show the search area on the sky, on three different dates): Topocentric predictions http://gaiafunsso.imcce.fr B. Carry (OCA), W. Thuillot (IMCCE) Register and contribute! IAU 30 GA - Wien - 2018 .