October 27, 2006 US SKA, CfA 1

The Square Kilometer Array and the “Cradle of Life”

David Wilner (CfA)

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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)

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• T Tauri, Herbig Ae stars: several l00’s of proto-Sun analogs, d ~ 140 pc, age 1-10 Myr

HD169142Dent et al. 2006

stardust

Protoplanetary Disks

SMA Raman et al. 2006

300 AU

HST Grady et al. 2006

1.3 mm1.3 mm

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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

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• 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

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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 Hya3.5 cm dust

Wilner et al.

NASA/JPL R. Hurt

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Embedded Protoplanets• protoplanet interacts

tidally with disk– transfers angular mom.– opens gap– viscosity opposes

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P. Armitage Bate et al.

r

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Small Bodies, Large Signatures

• Moon (S/2005 S1) in Keeler Gap, Cassini (May 1, 2005)

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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 135344 GM Aur

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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

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Nelson et al.

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New Facilities, New Territory

100 AU

SMAtoday

ALMA 2013?

10 AU1 AU

SKA2020?

?

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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

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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

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Protoplanetary Disk Assays

• molecules detected in handful of disks– ion-molecule reactions (HCO+)

– photo-processes (high CN/HCN)

– deuterium fractionation (DCO+)

– simple organics (H2CO)

• sensitivity limited

Thi et al.

TW Hya

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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. 2006Remijan et al. 2006

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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)

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End

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Relevance of Radio Regime

• bulk of disk material is “cold” (dark!) H2

– 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

– Mdisk~ 0.001 - 0.1 M (Beckwith et al. 1990)

• gas: spectral lines of trace species (CO, HCN, ...)– heterodyne >106: kinematics, chemistry

• no contrast problem with stellar photosphere

• high resolution imaging through interferometry