Astronomy 340 Fall 2007

1. Astronomy 340Fall 2007 29 November 2007 Class #25

2. Review • Pluto system • Odd orbit, 3 moons • Possible collision? • Triton • Neptune’s large moon • Retrograde orbit  likely gravitationally captured

3. A Little History • Gerard Kuiper and Kenneth Edgeworth “predicted” a distribution of small bodies in the outer solar system – 1940s • Real surveys began in early ’90s • 70,000 KBOs w/ d > 100 km (estimated) • 30 AU < a < 50 AU • Range of inclination/eccentricity • 1st KBO is really Pluto!

5. Bernstein et al 2004

6. Properties of TNOs • Green stars  scattered population • Red squares  classical KBOs • Lines are different power law fits • Surface density best fit by two power laws

7. Basic Orbital Properties • “Classical” • Low eccentricity, low inclination • 40 AU < a < 47 AU • “Resonant” • Occupying various resonances with Neptune  3:2, 4:3, 2:1 etc • a ~ 40 AU • “Scattered” • High eccentricity, high inclination

8. Distribution of TNOs

9. Population • Total mass ~ 0.5 Earth masses • Total number  unknown • > 1500 detected via surveys • Colors (Tegler et al 2003 ApJ 599 L49) • ~100 KBOs with photometry • “classical” KBOs are “red” (B-R > 1.5) • “scattered” KBOs are “grey” • Largely colorless (flat spectrum) • Primordial?

10. Classical KBOs Mostly between 42 and 48 AU Formed via “quiet accretion”

11. Orbital Populations • Reflect dynamical history of the outer solar system • Hahn & Malhotra (2005 AJ 130 2392) • N-body simulation • Neptune migration  previously heated disk • Populates the 5:2 resonance with Neptune • “scattered” KBOs largely affected by planet migration

13. Orbital Populations Hahn & Mulhatra

14. Scattered KBOs - orbits Trujillo, Jewitt, Luu 2000 ApJ 529 L103

15. Populations (Hahn & Malhotra 2005)

16. Explanation for Colors? Neptune migrates from 25 AU to 40 AU Scatters objects Objects at 40 AU are relatively unperturbed  surfaces reflect methane ice

17. KBO colors

18. KBO Colors vs Dynamics

19. Centaurs (Horner, Evans, Bailey 2004) • Eccentricity  e = 0.2-0.6 • Perihelia • 4 < q < 6.6 AU • 6.6 < q < 12.0 AU • 12.0 < q < 22.5 AU • Aphelia • 6.6  60 AU • Mean diameters ~ few hundred km

20. Centaurs – Dynamical Evolution • Dynamical lifetimes • Orbital decay rate  N = N0 e-λt (λ = 0.693/T1/2) • T1/2 ~ 2-3 Myr  scattered via interaction with giant planets • No correlation with color

21. Centaurs – Dynamical Evolution • Dynamical lifetimes • Orbital decay rate  N = N0 e-λt (λ = 0.693/T1/2) • T1/2 ~ 2-3 Myr  scattered via interaction with giant planets • No correlation with color • Origin? • “scattered” TNOs  scattered inward Hahn & Mulhatra

22. Sedna

23. Sedna • How do you measure the diameter? • Best fit orbit • R = 90.32 AU • a = 480 AU • e = 0.84 • i = 11.927 • Perihelion ~ 76 AU in 2075

24. Sedna

25. Quaoar

26. Quaoar

27. Quaor spectroscopy (Jewitt & Luu) Looks a bit like water ice

28. 2003 UB313 • 16 years worth of data • Orbital properties • a = 67.9 AU, e = 0.4378, i = 43.99 • Aphelion at 97.5 AU, perihelion at 38.2 AU (2257)

29. But are they really planets?

30. Eris - Spectroscopy • Big circles = broadband colors • Broad absorption = solid methane • Approximate diameter = Pluto’s • Hey, the thing has a moon….

31. Moons, moons everywhere….