Debris Disks are Signposts of Planet & Planetesimal Formation

1. Signposts of 2-4 Planets in a Mature Disk: Spitzer Evidence for Delivery of Organics and Water-Rich Material From the Kuiper Belt to the THZ of ~1 Gyr Old Sun-Like Star h Corvi C. Lisse (APL), C. Chen (STScI), M. Wyatt (Cambridge), A. Morlok (Open Univ), D. Watson, M. Puravan -kara, P. Sheehan (URoch), T. Currie (GSFC), P. Thebault (Observ. de Paris), M. Sitko (UCincinnati) Signposts of Planets Meeting, NASA/GSFC, 19 October 2011

2. Warm Dust in disks is rare (~2% of MS stars; Beichman et al. 2007). • Most Warm Dust Excesses are small; LIR/L* > 10-4 rare. • Warm Dust disks mainly detected by spectroscopic means. Debris Disks are Signposts of Planet & Planetesimal Formation • More than 100 resolved disk systems are now known • Cold dust in Kuiper Belts is common. Spitzer : > 20% of stellar systems have one; Bryden et al. 2006. Herschel: 30-40% of stellar systems have a detectable KB (Matthews et al. 2010). • Optically resolved MS systems disks are Kuiper Belts: Spitzer Survey of IRAS Bright Disks, Chen et al. 2006 HST, G. Schneider et al. HD 32297 HR 4976A Vega Beta Pic IRASSST/IRS SST/MIPS HD 181327 HD 141569A Fomahault HD 107146

3. h Corvi has a Bright Kuiper Belt, Containing ~1022 kg of Icy Dust Produced by Collisions JCMT/SCUBA submm images of η Corvi at 850 µm (15.8” resolution), 450 µm (at 13.7” resolution) and 450 µm with aneffective resolution of 9.5” (after Wyatt et al. 2005). In all images, the sub-mm emission is from cold KB dust at 100 – 150 AU (LTE ~ 30K) from the primary. Biolabate structure due to a tilted ring system is evident in the 160 um and high-resolution 450 µm images. 100 um (top) and 160 um (bottom) Herchel DEBRIS PACS FIR images of h Corvi, after Matthews et al. (2010). Circles in the upper left corner of each panel mark the nominal beam sizes.

4. ANDh Corvi (F2V, 18 pc) Evinces a Very High IR Excess Luminosity Due to Warm Dust at ~1 Gyr. 1000x Brighter! h Corvi is the 3rd brightest of Chen et al. 2006’s 59 IRAS-excess systems, and the only one which is a “mature” MS system of ~1.4 Gyr age, or about 1/3 of its total MS lifetime. η Corvi clearly has a high LIR/L∗ = 3 ×10−4 for its age, suggesting something unusual has occurred in this system.

5. Matthews et al.. 2010 Spitzer, Herschel, IRTF, & SCUBA Evidence for Cold & Warm Dust (2 Populations) Around h Corvi 350oK, ~3AU (THZ!) 35 oK, ~150AU (Kuiper Belt) F ~ 10-2 !!! Total SED for hCorvi showing the BVR/2MASS determined photospheric emission (green/blue), the MIR flux by IRAS and Spitzer, the FIR excess by Herschel, and the sub-mm excess by JCMT/SCUBA. Lisse et al. 2011 Spitzer IRS 5-35 um circumstellar excess flux (light blue) for η Corvi. Dark Blue – IRTF/SPeX excess, f~10-2. Green – simple water ice scattering model. Red – 390, 1700 K blackbody curves for comparison. Orange – Rocky HD113766A dust for comparison. GEMINI and VLT profiles of h Corvi 10/20 µm emission, showing the lack of resolved extension for the warm dust flux outside 3.5 AU. (After Smith et al. 2008)

6. Comparison of Mid-IR Emissivity Spectra for ~1 Gyr h Corvi, 2 Comets, and 4 Other Bright Dusty Disk Systems: Warm dust is non-asteroidal & VERY Primitive. Best Match is ~10 Myr Old HD100546 !! Comet-rich Herbig Cometary Material Cometary Material SiO2 S-type asteroidal material C-type asteroidal material Lisse et al. 2011 Spectral Comparison of the mid-IR spectra of hCorvi with the spectra of dust from: young, organic rich Herbig A0 star HD100546; two comets (Hale-Bopp and Tempel 1); a young F5 star building a terrestrial planet HD113766; the silica-rich debris created by hypervelocity impact in the A5V HD172555 system; and mature K0V MS star w/ dense asteroidal zody cloud HD69830. The most primitive dust, found in the disk of HD100546, produces the best match to the η Corvi dust.

7. Spitzer IRS Emissivity Spectrum of the h Corvi Warm Dust : Primitive Comet-like Materials + Impact Created Silica + Super-Abundant Organic Species (Nano-diamonds, Fullerenes, etc.). + Nanodiamonds, Fullerenes - Comet Ingredients- + Silica! => I5-10 km/s mpact Lisse et al. 2011 Left- Best fit model using small, solid, optically thin dust grains with silicate, silica, amorph carbon, metal sulfide, and water ice. The relative contribution of each species to the total observed flux is given by the amplitude of each emissivity spectrum.A 400K blackbody temperature dependence has been removed from the as-observed flux to create the emissivity spectrum. Middle- Residuals of the best-fit model to the Spitzer IRS emissivity spectrum. All of the usual silicate species have been accounted for and removed, as well as the water ice contribution to the emissivity. Right– Same residual plot, with the 5-15 µm region emphasized to present details of the poorly fit lines due to C-rich species.

8. Candidate Species for the Unusual 6 – 8 um Carbonaceous Features: Shock-Created Nano-Diamonds & Fullerenes Gaillou et al 2010 Cami et al. (2010) Left:Typical IR absorption spectra of “pink” diamonds. The mid-IR behavior is dominated by ppm C-N impurity vibrational features (A- and B-aggregates and the peak at 1430 cm− 1), by platelets at 1362 cm− 1, and by C-H stretches at 1405, 2785, 3107, 3236, 4496 cm− 1. Right: Continuum subtracted and forbidden emission line removed Spitzer spectrum of the PN Tc 1. Red arrows mark the wavelengths of all IR active modes for C60; blue arrows those of the four strongest, isolated C70 bands. Red & blue curves below the data are thermal emission models for all infrared active bands of C60 & C70 at temperatures of 330 K and 180 K, respectively. The broad plateau between 11 & 13 μm is attributed to emission from SiC dust. (Apparent weak emission bumps near 14.4, 16.2, 20.5 & 20.9 μm are artifacts.)

9. Silicate Mineralogy for h Corvi Warm Dust :Evidence for Very Primitive, Collision Processed Material Asteroids Olivine Pyroxene Comets Lisse et al. 2011 Silicate mineralogy for h Corvi versus that found in 5 comet systems, 3 primitive YSO disk systems, 5 dusty debris disks, and 2 dusty WD systems. The general trend observed is that the relative pyroxene content is high for the most primitive material (i.e., YSOs), & low for the most processed (i.e., white dwarfs). Young systems with material altered by high velocity impact processing, like HD172555 and h Corvi, lie above and to the left of the trend line.

10. Particle Size Distribution for the h Corvi Warm Dust: Dust is > 103 yr Old, in Collisional Equilibrum w/ Radiation Pressure Blowout of Smallest Particles Lisse et al. 2011 Lisse et al. 2011 The derived PSD is close to one in collisional equilibrium with small particles removed preferentially by radiation pressure and P-R drag. Error bars are estimated conservatively at 25% of the relative abundance at a given size.

11. Minimumh Corvi Warm Dust Mass : MCentaur to MKBO Observer Mean Equiv 19 um Approximate Object Distance1 Temp2 Radius3 Flux4 Mass5 (pc/AU) (K) (km) (Jy) (kg) Earth --- 282 6380 6 x 1024 Mars 1.5 AU 228 3400 6 x 1023 Mercury 0.5-0.7 AU 400 2400 3 x 1023 HD113766 (F3/F5) 130.9 pc 440 300 – 3000 1.85 ≥3 x 1023 Moon 0.0026 AU 282 1740 7 x 1022 HD172555 (A5) 29 pc 335 1000 – 2000 1022 – 1023 HD10647 (F9) 18 pc 30 (200-2000) 0.015 ~1 x 1023 HD100546 (Be9V) 103.4 pc 250/135 ≥ 910 203 ≥ 1 x 1022 h Corvi (F2) Cold Dust 18 pc 50(?) ≥ 1600 ≥ 6 x 1022 Pluto 40 AU 45 1180 1 x 1022 Asteroid Belt 0.1 – 5.0 AU Variable 3 x1021 Orcus 30 -45 AU 42-52 300 6 x 1020 Earth’s Oceans --- 282 6380 6 x 1020 Enceladus 10.5 AU 100 200 1 x 1020 Miranda 19.2 AU 65 235 7 x 1019 h Corvi Warm Dust (F2) 18 pc 360 ≥ 200 > 3 x 1019 – 3 x 1021 EF Cha 106 pc 480 120 3 x 1019 1996 TO66 38 – 48 AU 41 – 46 ~200 ~4 x 1019 Chiron 9 – 19 AU 65 – 95 ~120 ~1 x 1019 HD69830 12.6 pc 340 30 - 60 0.11 3 x 1017 - 2 x 1018 Zody Cloud 0.1 - 4.0 AU 260 4 x 1016 Asteroid 0.1 - 5.0 AU Variable 1 - 500 1013 - 1021 Comet nucleus 0.1 - 10 AU Variable 0.1-50 1012 - 1015 Hale-Bopp coma 3.0 AU 200 144 2 x 109 Tempel 1 ejecta 1.51 AU 340 3.8 1 x 106 - 1 x 107 (1) - Distance from Observer to Object. (2) - Mean temperature of thermally emitting surface. (3) - Equivalent radius of solid body of 2.5 g cm-3. (4) - System or disk averaged flux. (5) - Lower limits are conservative, assuming maximum particle size of 1000 µm, and ignoring optical thickness effects.

12. Dynamically Excited Kuiper Belt What‘s Going on in the h Corvi System ~3 AU THZ Planet ~3 AU Warm, Icy Dust MJup @100 AU? Scattered KBO(s) Originating at ~150 AU Over many Myrs, 1 or more KBOs totaling > 3 x 1019 kg (= a medium sized 100 - 200 km radius KBO) was scattered onto an in-spiraling orbit crossing into the inner reaches of the system, where it intersected the orbit of a planetary-sized rocky body located in the THZ. Much of the resulting debris was left in near-primary orbit at ~3 AU, where it continues to grind down. The dynamical process causing the KBO scattering continues to stir up collisions in the system’s Kuiper Belt, producing cold dust there as well.

13. The Amount & Kind of Warm Dust We Find in h Corvi , ≥ 3 x 1019 kg, is Similar to Predictions for the Delivery to the Earth During the LHB from the Lunar & Terrestrial Cratering Record. Nesvorny et al. 2009: “…The inner zodiacal cloud should have been >104 times brighter during the Late Heavy Bombardment (LHB) epoch ≈3.8 Gyr ago, when the outer planets scattered numerous comets into the inner solar system. The bright debris disks with a large 24-µm excess observed around mature stars may be an indication of massive cometary populations existing in those systems. We estimate that ∼1019 , ∼2 x 1018 & ∼2 x 1017 kg of primitive dark dust material could have been accreted during LHB by the Earth, Mars and Moon, respectively.” Jørgensen et al. 2009/2010: “…almost nothing of the Earth’s crust from even the end of this epoch, is preserved today. One of the very few remnants, though, is exposed as the Isua greenstone belt (IGB)and nearby areas in Western Greenland. During a field expedition to Isua, we sampled three types of meta-sedimentary rocks, deposited 3.8 billion years ago, that contain information about the sedimentary river load from larger areas of surrounding land surfaces (mica-schist and turbidites) and of the contemporaneous seawater (BIF). Our samples show evidence of the LHB impacts that took place on Earth, by an average of a seven times enrichment (150 ppt) in iridium compared to present day ocean crust (20 ppt). The clastic sediments show slightly higher enrichment than the chemical sediments, which may be due to contamination from admixtures of mafic (proto-crustal) sources. We show that this enrichment is in agreement with the lunar cratering rate and a corresponding extraterrestrial LHB contribution to the Earth’s Hadean-Eoarchean crust, provided the bulk of the influx was cometary (i.e., of high velocity and low in CI abundance), but not if the impactors were meteorites (i.e. had velocities and abundances similar to present day Earth crossing asteroids).

14. But Wait, There‘s More!Similarities Between the h Corvi Warm Dust & Sudan Urelite Meteorite Imply that the Urelites are fromthe Kuiper Belt, and that we have just witnessed a delivery of ice- and carbon-rich material. Lisse et al. 2011 The close match (above) between the Spitzer remote sensing and Almahatta Sitta lab transmission spectra of Sandford et al. (2010) led us to look into the current estimates of the origin and evolution of the Urelite Parent Body (UPB, right) – and the deduced UPB scenario is very similar to the h Corvi story, assuming a KBO hit a small rocky proto-planet in that system. Jennsikens et al. 2010

15. Conclusions: There is compelling Spitzer, IRTF, & Herschel evidence for a rare ongoing LHB-like event in ~1 Gyr old h Corvi (F2V), including delivery of significant amounts of water & organics to the THZ. • The h Corvi system contains an extended belt of cold (~35K) Kuiper Belt dust (Mass ~ 1022 Kg) at ~150 AU from the primary. • The system contains a warm (~360K) dust belt massing > 3 x 1019 kg (~1/1000th the mass of the Kuiper Belt dust) at ~3 AU from the primary, in the THZ. • This mass is about the mass of a large Centaur or middling Kuiper Belt object. • The warm dust is very primitive and also very water and carbon rich, and its spectrum matches best the dust in HD100546, an ~10 Myr old Herbig A0V. The dust also contains a fraction of amorphous silica produced by impact processes. • The amount of water tied up in the observed material is > 0.1% of the water in the Earth’s oceans, and the amount of carbon is also considerable, ~1018 kg. • The best model for what is going on in the h Corvi (F2V) system is that some process (e.g., planetary migration) is dynamically exciting the Kuiper Belt, and one of the excited objects was sent into the inner system > 103 yrs ago, where it collided with a planetary-class body at ~3 AU. This system could be a good analogue for the LHB processes in the Solar System at 0.6 – 0.8 Gyr.

17. 1 Gyr Should Be A Quiet Time For An Exo-system…. 1 Gyr 1 Gyr Wyatt 2009 Debris disks also have a large drop in sub-mm measures of mass starting at ~ 10 Myr age, and have hit a stable asymptote by 100 Myr. Wyatt 2009 Spitzer 24 um debris disk brightness is maximal around 10-20 Myr of age and dust formation mechanisms, like collisional aggregation, are strongest then. By 1 Gyr, the system should be mature, collisionally cold, and quiet. Most current models for terrestrial planet formation have embryos coalescing into Oligarchs at 10 - 30 Myr.

18. Derived Elemental Composition for the h Corvi Warm Dust : Abundances Look Impact-Altered Lisse et al. 2011 Derived elemental abundances for the h Corvi dust excess, relative to solar abundances, and as compared to other Spitzer dust spectra. Left : High photospheric subtraction, low amorphous carbon model abundances. Right : Low photospheric subtraction, high amorphous carbon model abundances. The Si relative abundance has been set = 1.0. The major refractory species, with the exception of S and Al, are all very depleted vs. solar, quite different than what is found cometary dust, which trends near solar.

19. Abstract We have analyzed the Spitzer IRS 5 – 35 um spectrum of the warm, ~360K circumstellar dust around the nearby MS star η Corvi (F2V, 1.4 ± 0.3 Gyr), a known IRAS excess object. The Spitzer spectrum shows clear evidence for warm, water- and carbon-rich dust at ~ 3 AU from the central star, uncoupled and in a separate reservoir from the extended sub-mm dust ring at 150 ± 20 AU reported by Wyatt et al. (2005). Spectral features similar in kind and amplitude to those found for ultra-primitive material in the ISO HD100546 spectra were found (water ice & gas, olivines & pyroxenes, amorphous carbon and metal sulfides), in addition to emissions due to impact produced silica and high temperature carbonaceous phases. A large amount, at least 2.8 x 1019 kg, of 0.1 – 1000 µm warm dust is present, the equivalent of a 140 km radius asteroid of 2.5 g cm-3 density or a “comet” of 260 km radius and 0.40 g cm-3 density, in a roughly collisional equilibrium distribution with dn/da ~ a-3.5. The mass present increases by (largest particle size/1000 µm)0.5, and the equivalent radii by the 3rd root of the mass. We conclude that the parent body for the warm dust was a Kuiper-Belt or Centaur-like body, which captured a large amount of early primitive stellar nebula material and kept it in deep freeze for ~1 Gyr, and was then prompted by dynamical stirring of its parent Kuiper Belt into interacting with a second body at ~3 AU at moderate velocities (5-10 km sec-1), slow enough to preserve some of the original refractory silicates but fast enough to alter a major fraction of the dust while delivering large amounts of water (> 1% of the mass of Earth’s Oceans) and carbon rich material.