October 27, 2006US SKA, CfA1 The Square Kilometer Array and the “Cradle of Life” David Wilner (CfA)

2 The Cradle of Life A Key Science Project –image dust emission from terrestrial planet formation zone of protoplanetary disks –assess biomolecules in ISM and disks –reach qualitatively new levels of sensitivity for SETI, including possible detection of “leakage” emissions (next talk, Jill Tarter)

3 T Tauri, Herbig Ae stars: several l00’s of proto-Sun analogs, d ~ 140 pc, age 1-10 Myr HD Dent et al star dust Protoplanetary Disks SMA Raman et al AU HST Grady et al mm

4 Planet Formation How do terrestrial and giant planets form? How much orbital evolution (migration)? Is our Solar System architecture typical? SKA uniquely accesses disk habitable zone –need cm waves: avoid high opacity –need milli-arcsec resolution: sub-AU at 140 pc –need very high sensitivity: thermal emission

5 flux density emitted by a disk element dA less than an Earth mass in sub-AU beam at 140 pc distance of nearby dark clouds SKA Sensitivity

6 Grain Growth and Settling detailed frequency dependence of dust emissivity is diagnostic of particle properties, esp. size SKA sensitive to cm sizes, predicted to settle to disk mid-plane and seed planetesimals TW Hya 3.5 cm dust Wilner et al. NASA/JPL R. Hurt

7 Embedded Protoplanets protoplanet interacts tidally with disk –transfers angular mom. –opens gap –viscosity opposes P. ArmitageBate et al.  rr

8 Small Bodies, Large Signatures Moon (S/2005 S1) in Keeler Gap, Cassini (May 1, 2005)

9 Inner Disk Holes SEDs of some disk systems show mid-ir flux deficits suggest inner holes, radii ~ 20 to 40 AU SMA imaging, 340 GHz, 250 mas, confirms evidence for dynamical sculpting by Jovian protoplanets Brown et al., Wilner et al SR 21 HD GM Aur

10 A Dynamic Process orbital timescales in habitable zone are short (t ~ 1 yr) synoptic studies track proper motions of mass concentrations make “movies” of inner disk structure Nelson et al.

11 New Facilities, New Territory 100 AU SMA today ALMA 2013? 10 AU 1 AU SKA 2020? ?

12 Biomolecules Universal prebioitic chemistry? Delivery to terrestrial planet zone? SKA uniquely accesses low excitation rotational transitions of large molecules –favorable partition function –low line confusion –high sensitivity

13 New Interstellar Molecules GBT: 8 (secure) new species in past 2 years Lovas, Hollis, Remijan et al. rich chemistry in dark clouds leading to large organic species

14 Protoplanetary Disk Assays molecules detected in handful of disks –ion-molecule reactions (HCO + ) –photo-processes (high CN/HCN) –deuterium fractionation (DCO + ) –simple organics (H 2 CO) sensitivity limited Thi et al. TW Hya

15 Bryden 1999 The Cradle of Life image terrestrial planet formation zone of disks –grain growth to pebbles –embedded protoplanets and sub-AU tidal gaps –track motions assess biomolecules –disk abundances –locations Remijan et al. 2006

16 Philosophical Remark Future optical/infrared searches may reveal terrestrial exoplanets that can harbor life Radio observations into the habitable zone of protoplanetary disks will help us to understand why they are there (and why we are here)

17 End

18 Relevance of Radio Regime bulk of disk material is “cold” (dark!) H 2 –probed only through minor constituents dust: continuum emission with low opacity –dF  = B (T)   dA, detect every dust particle; millimeter flux ~ mass, weighted by temperature –M disk ~ M  (Beckwith et al. 1990) gas: spectral lines of trace species (CO, HCN,...) –heterodyne  >10 6 : kinematics, chemistry no contrast problem with stellar photosphere high resolution imaging through interferometry