Observing How Habitable Conditions Develop (Or Not) in Protoplanetary Disks

Colette SalykNational Optical Astronomy Observatory

Credit: JPL-Caltech/T. Pyle (SSC) Credit: NASA

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Why studying protoplanetary disks is important for understanding habitability

• Planet formation “laboratory” – ground truth for our ideas about how planets form and habitability develops

Even if you don’t care how planets form…

Milky way diameter: 40 kpc(120,000 light years)

Microlensing planets: 5 kpc

Kepler planets: 2 kpc

Imaged planets: 0.2 kpc

Credit: Exoplanet app

Planet detection remains difficult at large distances, and characterization even more so

Why studying protoplanetary disks is important for understanding habitability

• Planet formation “laboratory” – ground truth for our ideas about how planets form and habitability develops

• Understanding formation process allows us to extrapolate to the rest of the galaxy/universe

• Overview of what we do and don’t know about protoplanetary disks

• Current studies of development of Goldilocks properties:– Location– Planet size and type– Chemistry

Composed of gas and (opaque) dust, Few 100 AU in size

CO velocity in HD 163296 (ALMA)

de Gregorio-Monsalvo et al. 2013

Opaque disks in Orion (Hubble)1800 AU

Small (but evolved) dust, consistent with olivine composition

Spitzer spectra of Si-O stretch

Chondrule from American Museum of Natural History meteorite collection

Kessler-Silacci et al. 2006

Data

Models

Small (but evolved) dust, consistent with olivine composition

Chondrule from American Museum of Natural History meteorite collection

Spitzer spectra of Si-O stretch

Kessler-Silacci et al. 2006

Data

Models

Protoplanetary disks are ubiquitous*

Kraus & Ireland, 2011

*around sun-like stars in nearby star-forming regions

Protoplanetary disks last a few Myr

Kraus & Ireland, 2011

Masses are consistent with Minimum Mass Solar Nebula, or slightly lower

Ophiuchus data from Andrews et al. 2007

Masses are consistent with Minimum Mass Solar Nebula, or slightly lower

Ophiuchus data from Andrews et al. 2007∨

small

• Planet size and location: Snow lines and disk dispersal

• Chemistry: Chemical inventories of planet forming regions

Active research related to habitability

What processes determine planetary size and location?

Gas giantsTerrestrial planets

What processes determine planetary size and location?

Gas giantsTerrestrial planets

The “snow line” – an increase in solid surface density

What is the expected location of the snow line?

What is the expected location of the snow line?

Gas giantsTerrestrial planets

The “snow line”

Habitable zone

Multi-wavelength observations of water vapor measure snow line locations

ice lineK. Pontoppidan

First measured locations of snow lines in disks

Meijerink+ 2009Zhang+ 2013

First measured locations of snow lines in disks

Meijerink+ 2009Zhang+ 2013

See poster by Sandra Blevins for an update!

Gas giantsTerrestrial planets Ice giants (super Earths?)

Planet type affected by disk dispersal

Dispersal of disk gas also affects planet migration

Snapshot of disk surface densitywith planet undergoing migration

P. Armitage

1 10 100

# of planets

Orbital Period [days]

Hot Jupiters

How do disks evolve/disperse?Disk winds

Blandford & Payne 1982Pudritz & Norman 1983Cartoon inspired by Bai et al. 2013

B wind

accretion

Molecular emission lineshapes and images – evidence for disk winds?

Pontoppidan+ 2009; also Bast+ 2011

Flux

Velocity

ALMA CO velocity field

Salyk+ in prepBrown+ 2013

Vibrational CO

How do disks evolve/disperse?Photoevaporative winds wind

FUVEUVX-ray

How do disks evolve/disperse?Photoevaporative winds wind

FUVEUVX-ray

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Main open question: How quickly do disks dissipate at each disk radius?

Observations of photoevaporation tracers measure location and mass-loss

[Ne II] emission from two disks + models

Pascucci & Sterzik 2009

• Chemistry: Chemical inventories of planet forming regions

Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001

CI chondrite abundances vs. solar abundances(R ~ 4 AU)

Earth abundances vs. solar abundances(R = 1 AU)

Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001

N2, HCN, NH3, organics ?

CO, CO2, organics, graphite?

Earth abundances vs. solar abundances(R = 1 AU)

Solar data from Grevesse et al. 2010Chondrite data from Allegre et al. 2001

What is the correct chemical pathway? Inheritance or reset?

Maximum “reset”

Maximum “Inheritance”

Resemblance between cometary and cloud ice compositions = an inheritance assumption

Data from Mumma & Charnley 2011 (and references therein)

Cometary abundance% relative to water

Cloud abundance% relative to water

Evidence for reset in the solar system: CAIs and chondrules

Chondrule

Calcium Aluminum-rich Inclusion (CAI)

Thin sections from the American Museum of Natural History meteorite collection

Carr & Najita 2008Also, Salyk+ 2008

The study of chemistry in inner disks was enabled by the Spitzer InfraRed Spectrograph (IRS)

O,C,N inventory in inner disks is being measured

Pontoppidan+ 2014

O C N

Fraction

Evidence for reset in disks: O,C,N inventory different from birth cloud

Salyk et al. 2011; Öberg et al. 2011

Evidence for reset in disks: Variability in disk chemistry

Banzatti et al. 2012

See poster by Andrea Banzatti

Current: Partial chemical inventory, evidence for reset

Yet to come: Chemical differences between disks, and as a function of radius

• Basic protoplanetary disk properties have been characterized

• Studies of development of Goldilocks properties ongoing:– Location– Planet size and type– Chemistry

Conclusions

Measuring snow linesObserving disk evolution/dispersal

Chemical inventory in planet-forming regions, evidence for reset, details yet to come

Questions about observing disks?