Explorations of the Outer Solar System. B. Scott Gaudi Harvard-Smithsonian Center for Astrophysics

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1 Explorations of the Outer Solar System B. Scott Gaudi Harvard-Smithsonian Center for Astrophysics

2 The Known Solar System How big is the solar system? a tidal R 0 M Sun M Galaxy 1/3 200,000AU How big is the observed solar system? Pluto, Kuiper Belt, a KB 50AU Sedna, a Sedna 500AU!

4 The Known Solar System The observed portion of the solar system constitutes ~ one billionth of its entire volume!

5 The Known Solar System What do we know about the solar system? Where did all this stuff come from? Why do we care?

6 Star Formation 101 Molecular Cloud Cores Collapse Ignition/Outflow Protoplanetary Disk Planetary System Hogerheijde 1998

7 Planet Formation 101 Core-accretion Model Dust Planetesimals (non G) Planetesimals Protoplanets Protoplanets Terrestrial Planets Inner Solar System (<3AU) Protoplanets Gas Giants Outer Solar System (3AU-40AU) Protoplanets Planetoids Distant Solar System (> 40AU)

8 The Kuiper Belt General Properties 1 st member discovered in 1992 (1992 QB1; Jewitt & Luu 1993) ~850 known. Total mass ~1% Earth Radial Extent (30-50)AU, peak near 45 AU. (Trujillo & Brown 2001)

9 The Kuiper Belt Dynamical Classes Classical Resonant Scattered Extended Scattered?? (Gladman et al. 2001)

10 The Kuiper Belt Dynamical Classes Classical Resonant Scattered Extended Scattered?? Sedna (Elliot et al. 2005) (Gladman et al. 2001)

11 Sedna The Last Outpost Discovered in 2003 by Brown, Trujillo, Rabinowitz Usual Properties Orbit Semimajor axis a ~ 500 AU Perihelion q ~ 80 AU Size Diameter ~ 1500 km Color Very Red Slowly Rotating? Period P ~ 20 days? Companion? PSedna 20days?

12 Sedna A Binary? No! At least 5%-10% of KBOs in binaries What about Sedna? (Noll et al 2002) (Noll et al 2004)

13 Sedna A Better Light Curve Used the 6.5m MMT telescope Kris Stanek, Matt Holman, Joel Hartman, Brian McLeod P Sedna 10hours

14 Sedna A Better Light Curve Used the 6.5m MMT telescope Kris Stanek, Matt Holman, Joel Hartman, Brian McLeod Normal! P Sedna 10hours P Sedna 20days?

15 Sedna Open Questions Extended Scattered Disk? How did it get there? Passing Star? Rogue Planet? How many more are out there? Could have only found Sedna over ~1% of its orbit (Kenyon & Bromley 2005) semimajor axis (AU)

16 Limitations of Direct Measurements Strong scaling with size and distance Flux R 2 d Detection without Light? Gravitational Lensing Gaudi & Bloom (2005) Occultations Bailey (1976) Dyson (1992) Brown & Webster (1997) Roques & Moncuqeut (2000) 4

17 Gravitational Lensing α βd d α = 4GM βdc 2

18 Gravitational Lensing α = 50µas M M d 100AU 1 β 1" 1

19 Gravitational Lensing Requirements Moving object Dense Star Field Faint Stars Precise Astrometry Time Series Π Discovery All-Sky Synoptic Survey Π = 30' d 100AU 1

20 Gravitational Lensing (Gaudi & Bloom 2005)

21 Gravitational Lensing GAIA All-Sky Astrometric Mapper All stars down to V~20 (one billion stars!) Astrometric accuracy Bright Stars: ~30 µas Faint Stars: ~1400 µas Measure each star ~50 times (Gaudi & Bloom 2005) 5σ

22 Occultations

23 Principles of Occultations Physical Parameters R, d, v Scales angular size velocity proper motion θ = R d R d 140µ as 10km 100AU AU v = v cosϕ d km s at opp. µ = v d 1"hr 1-1 v d 100AU 30 km

24 Principles of Occultations Observables Duration Δt bθ Δt = 2tK 1 b Crossing Time 2 t K = θ µ R 0.3s 10km v km s 1 Δt Statistical information only

25 Principles of Occultations Observables Ingress/Egress time Impact parameter b Dimensionless source size θ * bθ θ * R 20µ as R * Sun d* 250pc 1 θ θ * ρ = * 1 R km 1 d R 100AU R * Sun d* 250pc

26 Principles of Occultations Observables Fringe Spacing Dimensionless Fresnel angle θ F λ θ F = d λ 4µ as 545nm ρ F = θ F θ λ nm 1/ 2 1/ 2 d 100AU d 100AU 1/ 2 1/ 2 R 10km 1

27 Principles of Occultations Observables Δt, ρ, ρ * F Parameters d R = = λ ρ * 2 2θ * ρf λ λ v = 2θ ρ * 2 2θ * ρf ρ 1 * 2 t * ρf K 2 R, d, v θ * θ F

28 Example Lightcurves Light curves 10% errors (V=14) 5 Hz sampling

29 Occutations by Binaries Detection Rate? Binary properties Primary size Size ratio Separation Photometric properties Sampling rate Photometric errors

30 Occutation Surveys Challenges Short event duration Δt R 0.6s 10km Low event rate v km s Γ = dr2θµ Σ 1

31 Occutation Surveys Challenges Short event duration Δt R 0.6s 10km Low event rate km s Γ = dr2θµ Σ Monitor >1000 stars v 3 yr 1 1 (R<10km)

32 Occutation Surveys Taiwanese-American Occultation Survey (TAOS); Charles Alcock, PI Telescopes & Hardware Four 50 cm robotic telescopes f/1.9 2 square degree 2Kx2K cameras Jade Mountain, Taiwan Data 2000 stars 5Hz 10% precision Short exposure times

33 Occutation Surveys Shutterless Zipper mode

34 Occutation Surveys Next Generation Survey Requirements Higher cadence Improved photometry (reduced sky background) Color information Space based Modeled after Kepler Prism TAOS

35 Occutation Surveys Next Generation Survey 600m at 45 AU 600m at 100 AU

36 Occutation Surveys TAOS Next Generation

37 Summary Many unanswered questions about the Kuiper belt. Outer solar system largely unexplored. Sedna is weird in many ways, but not its rotation period. Reflected light detections limited. Can detect dim or dark but massive objects with GAIA. Occultation can be used to detect distant, small objects. Light curves subject to degeneracies Additional parameters enable parameter measurement High cadence and accurate photometry needed Binaries can be detected via occultations Occultation surveys are challenging Short duration Low event reate

Class 2 Solar System Characteristics Formation Exosolar Planets

Class 2 Solar System Characteristics Formation Exosolar Planets Class 1 Introduction, Background History of Modern Astronomy The Night Sky, Eclipses and the Seasons Kepler's Laws Newtonian Gravity General Relativity Matter and Light Telescopes Class 2 Solar System