Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May...
Transcript of Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May...
![Page 1: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/1.jpg)
Paolo Tanga
Solar System science by Gaia observations
P. TangaObservatoire de la Côte d’Azur
![Page 2: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/2.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Gaia and the Solar System…• Asteroids (~400.000 – most known)
– Mainly Main Belt Asteroids (MBA)– Several NEOs– Other populations (trojans, Centaurs,..)
• Comets– Primitive material from the outer Solar System
• « Small » planetary satellites– « regular »– « irregular » (retrograde orbits)
• Gaia will probably NOT collect observations of « large » bodies (>600 mas?)– Main Planets, large satellites– A few largest asteroids
![Page 3: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/3.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
The scanning law
Sole
Spin axis
Spin axis trajectory,4 months
4 rotations/day
Sun trajectory,4 months
45°
Rotation axis movement
Scan path4 days
Spin axis trajectory4 days
Scan path in 4 days
![Page 4: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/4.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Observable region on the ecliptic
~ 60 detections/ 5 years for Main Belt asteroids
~ 1 SSO object in the FOV every second around the ecliptic
• Discovery space: – Low elongations
(~45-60°)– Inner Earth Objects
(~unknown) – Other NEOs
unobservable
unobservable
Sun
Gaia
![Page 5: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/5.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 20115
How many asteroids with Gaia?• Evolution of the number of entries H < Hlim
Gaia detection limit
Probable total number
Nknown H <16 ~ 250 000margin for discovery H < 16
Nnew H <16 ~ 150 000
![Page 6: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/6.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Gaia data for asteroids
• Astrometric Field
– Main source of photometric and astrometric data
– Read-on window assigned on boardaround each source
– Window is tracked during the transit– For most sources the signal is binned
across scan
Best accuracy in the « along scan »directionAcross Scan uncertainty ~ window size
![Page 7: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/7.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Windows on moving sources• Windows are allocated from ASM centroiding
– centroiding errors lead to offset in the window– transit velocity errors lead to a drift in the window
• A moving object will also drift relative to the window– the total effect depends on the window size and Val
SM
Signal recorded
AF1 AF2
![Page 8: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/8.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Velocity distribution
• simulation on 5,000 objects– main-belt, NEOs
• motion detectable over 1 transit
Val
Vacσ ~ 7 mas/s
σ ~ 12 mas/s
mas/s
%
-40 -30 -20 -10 0 10 20 30 400
1
2
3
4
5
6
7
8 along-scan
mas/s
%
-40 -30 -20 -10 0 10 20 30 400
1
2
3
4
5across-scan
![Page 9: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/9.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Solar elongations
![Page 10: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/10.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Statistics on 20000 brightest objects
Phase angles
![Page 11: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/11.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Expected properties of Gaia data: summary• 1 linear signal per CCD column
– 2D data available in some cases– Loss of data due to motion
• High accuracy in the along scan (AL) direction, poor accuracyacross-scan (AC)– Resulting in strongly correlated ucertainties on single-epoch equatorial
positions
• 50-70 observations of a given Main Belt Asteroid over 5 years
• Low elongations (~45°) accessible
• Frequent subsequent observations in the two FOVs
• parallax effect relative to Earth (observations from L2)
![Page 12: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/12.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Science goals• Systematic survey down to 20 mag ~ 3x105 objects
• Main belt• NEOs
• Orbits : virtually all object observed - x30 better than nowhigher resolution of dynamical families
• Masses from close encounters ~ 100 masses expected
• Diameter for over 1000 asteroids : shape, density• Binary asteroids• Photometric data in several bands : albedo, taxonomic classification• Light curves over 5 years : rotation, pole, shape• Space distribution vs. physical properties• Perihelion precession for 300 planets : GR tests
![Page 13: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/13.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Astrometry orbit refinement• Orbit reconstruction from simulated data
– point sources & gravitational interaction– solar system perturbations
> 102 better than current accuracy
Mouret et al. 2007D
ensi
ty
-
+
10 -8
![Page 14: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/14.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
λp = 30
βp = 60
b/a = 0.7
c/a = 0.5
P = 7h.527
φ0 = 0.4
Simulated Gaia photometry
Δ(mag) wrt first observation
Orbit of 39 Laetitia
A. Cellino, P. Tanga, M. Delbo
![Page 15: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/15.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Photometry Shapes• 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
• Choice for Gaia:
– Three-axial ellipsoids
Animation: M. Delbo
![Page 16: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/16.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Size of the asteroids•• DirectDirect size determination for over
1000 asteroids• Good quality sizes for D>40km • Object’s size at different epochs
overall shape• Binarity
Signals for different source diameter
unresolved
θ ~ 100 mas
θ ~ 300 mas
![Page 17: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/17.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
RP/BP Taxonomic classification•• Taxonomy classifies asteroids on the basis of visibleTaxonomy classifies asteroids on the basis of visible and nearnear--IR IR
reflectance spectroscopyreflectance spectroscopy–– Based on ~1000 objects todayBased on ~1000 objects today
•• Gaia special features:Gaia special features:–– High solar elongationHigh solar elongation–– Blue spectrum coverageBlue spectrum coverage–– Several Several ““bandsbands””
Preliminary investigation on Preliminary investigation on earthearth--based observationsbased observations
•• LimitationsLimitations–– ……no albedo no albedo ambiguity E,M,Pambiguity E,M,P……
•• automatic classifier developed automatic classifier developed for Gaia for Gaia
Gaia taxonomyGaia taxonomy
Normalised reflectance
![Page 18: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/18.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
How much is / will be known
Property today Gaia
astrometry ~ 0"5 0"005
rotation periods 3000 ~100,000
shapes, poles ~200 ~100,000
spectral type ~ 1800 ~200,000
masses, σ < 60% ~ 40 150
size , σ < 10% ~ 500 1000
satellites ~ 20 (MBA) ?
![Page 19: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/19.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Processing of SSO data
![Page 20: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/20.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
The DPAC
SSO
![Page 21: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/21.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
SSOs in the Gaia DPAC• Coordination Unit 4
– manager : D. Pourbaix; deputy: P. Tanga– Implementation of software in the Data Processing Center– ~ 20 european astronomers working on SSOs
Two pipelines for SSO:
• Short-term (daily) processing– Working on 24h of data– Fast processing for identifying anomalous/unknown asteroids
Triggering of alerts
• Long term processing– Best accuracy– Complex object model (shapes, motion,…), best astrometric solution,
all effects taken into account– Aims: intermediate final data releases
![Page 22: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/22.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Daily pipeline schemefor SSOs
IDTInitial Data Treatment
Initial Filterbased on object motion
during the focal plane crossing
Comparison to ephemerisof known objects
Linking of observations over ~48 hoursinto « bundles »
Preliminaryshort-arc orbitIdentification
certain?
YES
STOPCandidate « new » SSO
CU 4
NO
SSO database
IDTInitial Data Treatment
![Page 23: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/23.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Gaia Follow-Up-Network for SSO• Validation of SSO nature of the «new» objects
– Ground based recovery can discriminate « false » and « true » SSO– Reliability verification of the daily processing chain
• Recovery of the highest possible number of – New objects, discovered by Gaia– Objects with « poor » orbits ( ambiguous identification)
• Improve orbit accuracy– a single ground-based detection can “collapse” the uncertainty of an
orbit
• Advantages– contamination of data sent to Minor Planet Center during the early
mission operations is avoided– the science impact of the mission is maximized
![Page 24: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/24.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Long-term processingIDTInitial Data Treatment
Comparison to ephemerisof known objects
Linking of all availableobservations for eachobject into « threads »
CU 4SSO
database
Physicalproperties Global parametersAccurate
orbits
Mission outcome
• No external data sources used for DPAC processing– probably for validation purposes only
![Page 25: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/25.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
Possible actions triggered by the Gaia output• Further data exploitation
– Computation of proper elements, new dynamical familyclassifications
– Deeper analysis of anomalous sources (suspect binaries, comets…)
• Obtention of new data– TNO/asteroid occultations– Complementary observations:
• Spectra• Photometry• Astrometry (candidates for mass / Yarkovsky determination)
• Exploitation by associating data of other surveys:– Pan-STARRS, LSST, Spitzer & WISE …
This is the reason why we are in Pisa now!
![Page 26: Solar System science by Gaia observations · Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011 λ p = 30 β p = 60 b/a = 0.7 c/a = 0.5 P = 7h.527 φ 0 = 0.4 Simulated Gaia](https://reader034.fdocuments.net/reader034/viewer/2022052021/60362aef580c2647732639d7/html5/thumbnails/26.jpg)
Paolo Tanga, Gaia Solar System Science – Pisa May 4-6 2011
The End…