Elisabetta Dotto INAF-OAR Italy

1. Linking Jupiter Trojans to the populations of Centaurs and TNOs: analysis of the physical properties Elisabetta Dotto INAF-OAR Italy Catania, 3-7 July 2006

2. The Origin of Jupiter Trojans • Capture of fragments of jovian satellites • Trapping of planetesimals orbiting nearby the proto-Jupiter • Mass growth of the planet • Gas drag capture of short-period comets • Jupiter Trojans, like KBOs and the scattered disk, originated in the planetesimal disk which drove the planetary migration.

3. Jupiter Trojans So far we know: 1600 objects (930 L4 and 670 L5) estimated population: In L4 more than 105objects with D 2 km 6400 objects with D>10 km (Jewitt et al. 2000) Orbits stable over the age of the Solar System

4. The Size population (Jewitt et al. 2000) Two different power law size distributions. Larger objects represent the primordial population, while trojans with r < rc are products from the larger ones by collision shattering. rc ~ 30 km Jupiter Trojans are at least as collisionally evolved as main belt asteroids. This is supported by the identification of several dynamical families, both in L4 and L5.

5. Only 4709 Ennomos has an extremely elevated albedo (~0.13) The albedo values (Fernandez et al. 2003)

6. Albedo Values of TNOs and Centaurs

7. Visible and near-infrared spectra of Jupiter Trojans Jewitt and Luu, 1990 Jones et al. 1990 Barucci et al. 1994 Fitzsimmons et al. 1994 Luu et al. 1994 Lazzarin et al. 1995 Dumas et al. 1998 Cruikshank et al. 2001 Emery and Brown 2001 Emery and Brown 2003 All the spectra appear featureless The last majority of JT belongs to the D taxonomic class, but P and C-types are also present

8. Visible and near-infrared spectra of Jupiter Trojans Jewitt and Luu, 1990 Jones et al. 1990 Barucci et al. 1994 Fitzsimmons et al. 1994 Luu et al. 1994 Lazzarin et al. 1995 Dumas et al. 1998 Cruikshank et al. 2001 Emery and Brown 2001 Emery and Brown 2003 (Barucci et al. 2003) All three Centaurs show the 1.5 and 2 micron bands of water ice, while there is not spectral evidence for ice on Hektor

9. Visible and near-infrared spectra of Jupiter Trojans (Emery and Brown 2004) Water ice and hydrated silicate features were not detected upper limits of a few % for water ice and up to 30% for hydrated silicates

10. A V+NIR Spectroscopic Survey of Jupiter Trojan members of dynamical families (Fornasier, Dotto et al. 2004, 2006; Dotto, Fornasier et al. 2006) • Several observing runs at ESO-NTT, ESO-VLT and ENO-TNG • Family members selected among the list by the Beauge and Roig PETrA project • Visible spectra: 80 objects (47 L5 and 33 L4) • NIR spectra of 24 objects

11. (Dotto, Fornasier et al. 2006)

13. (Fornasier, Dotto, et al. 2006) The majority of JT belongs to the D class. The abundance of C-types in L4 is mainly due to the Eurybates family

14. (Fornasier, Dotto, et al. 2006)

15. L5: <S> = 8.84 ± 2.41 % / 103 Å L4: <S> = 4.57 ± 3.45 % / 103 Å (Fornasier, Dotto, et al. 2006) • No evidence of a possible color-dimension trend • L4 and L5 clouds have similar spectral slopes • The Eurybates family strongly contributes to the population of small spectrally neutral objects

16. (Fornasier, Dotto, et al. 2006) • No evidence of a possible color-dimension trend • L4 and L5 clouds have similar spectral slopes • The Eurybates family strongly contributes to the population of small spectrally neutral objects

17. 5 TNOs 4 Plutinos 4 3 3 2 2 1 1 Number of objects 0 0 -10 0 10 20 30 40 50 60 -20 -10 0 10 20 30 40 50 60 Jupiter Trojans Centaurs Centaurs 20 4 15 10 2 5 0 -10 0 10 20 30 40 50 60 0 8 16

18. B-V B-V (Fornasier, Dotto, et al. 2004)

19. (Fornasier, Dotto, et al. 2006)

20. Conclusion • Strong homogeneity

21. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates)

22. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures

23. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition

24. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition • Some differences can be attributable to space weathering effects

25. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition • Some differences can be attributable to space weathering effects • L4 and L5 clouds are spectrally very similar (with the exception of the Eurybates family)

26. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition • Some differences can be attributable to space weathering effects • L4 and L5 clouds are spectrally very similar (with the exception of the Eurybates family) • No relation has been found between color indices and dynamical characteristics

27. Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition • Some differences can be attributable to space weathering effects • L4 and L5 clouds are spectrally very similar (with the exception of the Eurybates family) • No relation has been found between color indices and dynamical characteristics • Small objects have the same dispersion in the spectral slope than the large ones

28. ` Conclusion • Strong homogeneity • Dominance of P- D- types (with the exception of Eurybates) • No diagnostic spectral signatures have been found, in particular no ice signatures • All the objects seem to have similar surface composition • Some differences can be attributable to space weathering effects • L4 and L5 clouds are spectrally very similar (with the exception of the Eurybates family) • No relation has been found between color indices and dynamical characteristics • Small objects have the same dispersion in the spectral slope than the large ones On the basis of these results we can suppose that the parent bodies of all the analysed families had a quite homogeneous structure. The whole population of Jupiter Trojans is quite homogeneous, even considering the two L4 and L5 clouds. The only strong exception seems to be the Eurybates family.

29. Open questions: 1. How evolved Jupiter Trojans are? 2. Which is the composition of Jupiter Trojans? 3. The water ice “enigma” 4. Why Jupiter Trojans are so different from some TNOs and Pholus-type Centaurs? 5. Origin and early evolution are still unknown 6. Why family members are so similar to the background (with the exception of Eurybates)? 7. Where does the Eurybates progenitor come from?