Occultations of the Galilean Satellites - How Accurate are the Ephemerides ?
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Occultations of the Galilean Satellites -
How Accurate are the Ephemerides?
Tony Mallama
32nd Annual Meeting of IOTA
2014 July 12-13, College Park MD
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Galilean Satellite Ephemerides
• JPL JUP-seriesIncludes astrometry from Galileo Orbiter
• IMCCE (Paris) L-seriesOmits astrometry from Galileo Orbiter
• JPL E-series1990s vintage
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Ephemeris Accuracy
• Analyzed 20 years of Jovian eclipse timings• Computed observed-minus-calculated (O-C)• Searched for anomalies in O-C plots
Reference: Mallama, Stockdale, Krobusek and Nelson, 2010. Icarus, 210, 346-357
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Io O – C
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Io Resonance Errors
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Europa O – C
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Europa Resonance Errors
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Summary of Resonance Errors
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Astrometric Accuracy
Random Photometric Errors (scatter)Assume that they are zero
Systematic (modeling) Errors
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Albedo Features and Limb-Darkening
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Photo-Center Offsets
Albedo SolarIo 68 209Europa 107 221Ganymede 113 303Callisto 93 255
Estimated maxima in kilometers
Mallama. 1993. J. Geophys. Res. 98, 18,873-18,876
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Uncertainties in Mutual Event ResultsComputed for PHEMU 2003
Emelyanov. 2009. MNRAS 394, 1037-1044
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Comparison Between Uncertaintiesof Ephemerides and Astrometry
Unit conversion (for ephemeris uncertainty)
JUP230 resonance error for Europa = 1.1 s
Velocity of Europa = 13.7 km/s
1 km at Jupiter distance = 0.00026 arc second
Arc second error in JUP230 = 0.004
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Comparison Between Uncertaintiesof Ephemerides and Astrometry
Worst case for JUP230 = 0.004 arc secondBest case for astrometry = 0.044 arc second
Bottom line:JUP230 is 10x more accurate than
mutual occultation astrometry
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Comparison Shown Graphically
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Comparison Shown Graphically
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Comparison Shown Graphically
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Comparison Shown Graphically
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Summary
The current JPL ephemerides for the Galileansatellites are much more accurate thanastrometry from mutual occultations.
However, occultation results are still being collected and they will continue to contributeto the development of future ephemerides.
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Backup Slides
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Egress from Shadow of Jupiter
Reference: Mallama, Stockdale, Krobusek and Nelson, 2010. Icarus, 210, 346-357
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Model of Eclipse by Jupiter
Reference: Mallama, Stockdale, Krobusek and Nelson, 2010. Icarus, 210, 346-357
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Mutual Events versus E3 Predictions
Reference: Mallama, 1992. Icarus, 95, 309-318